# Glow plug question



## ghost1 (May 10, 2016)

I have a Cub 7235 (Mitsubishi 3 cylinder) and now that the weather is cooling off, it won't start unless I use starting fluid "sparingly" as I'm reading not a good idea with glow plugs. It's getting 9.8 volts to the plugs, however, the glow plug indicator is not lighting up (it's the coil type). Is that enough voltage to plugs and is there a way to test them to see if good?


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## harry16 (Dec 8, 2011)

Hello ghost1,
Glow plugs present a heavy load to the battery, so 9.8 volts may be OK. Remove the glow plug bus bar and check the glow plugs with an ohmmeter. Each glow plug should measure about 1-3 ohms, low resistivity. If a glow plug measures near 0 ohms, it is shorted and no good. If it reads infinity, the plug is open circuit and no good. If you find a bad one, replace all three, as they all have the same time on them and the others are ready to fail in the near future.


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## thepumpguysc (Jan 25, 2015)

Another way is to remove them carefully. Take them over to your battery charger & hook the - to the body & the + to the top.. now turn it on and count by 1000.. 1 1000, 2 1000.. etc. it should be cherry red by 10, 1000.
Harry is right on the replacement of all 3 if 1 is slow or bad.. just don’t forget to pitch the bad ones in the trash & put the others on the shelf for an emergency..


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## Hacke (Feb 22, 2011)

Consult the wiring diagram before any action. If there is a coil type indicator, chanses are that the plugs are made for a lower voltage than 12 V. The plugs working voltage depends on how they are connected. 

When you crank, the plugs are connected directly to the system (without the coil) but the starter motor lowers the system voltage. In order to make the plugs glow at this lower voltage, they have a lower working voltage than 12 V.

At pre-heating, another circuit is used where the coil is in series with the plugs and makes a voltage drop. It also works as an indicator; When it glows, current flows through it and the plugs.

If you connect 12 V to a glow plug for this type of system, chanses are you will fry the plug. A short while may work, but why risk it? Better to test the plugs with it's working voltage.

I do not know if this is the correct plug, but it fits Cub Cadet 7235, it is for 7 V:
https://bestfarmparts.com/Cub-Cadet...-7235-7272-7273-7274-7275-7300-7305-7530-7532


Check the wiring diagram first.


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## ghost1 (May 10, 2016)

Thanks for the replies. It does have a "coil" type indicator and it did glow red when I first purchased tractor. I have disconnected the plugs and they read just less than one ohm after meter bounces around for a few seconds. When key switch if turned to the preheat position, I am reading 12 volts where wire lead comes out of harness and hooks to first plug. When key is turned to engage starter, that 12 volts is zero. So I'm assuming the system is not activating plugs when starter is actually trying to start engine. The coil indicator doesn't glow red in any situation.


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## sixbales (May 18, 2011)

Try disconnecting the glow plugs and measure the voltage to them in the preheat and crank positions. If you're not getting power to them in the crank position, keyswitch is faulty.


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## Hacke (Feb 22, 2011)

The coil resistance is depending on the current in a closed circuit. If you measured the unhooked lead from the coil, there will only be a very small current going through the coil and the instrument. That current is not enough to produce the heat in the coil that lifts the resistance. Therefore 12 V. It may also be something in the harness backfeeding 12 V, if you put a load on it, it "disappears".

Get yourself a wiring diagram, you need to find out how things are supposed to work and what you are measuring. There may be a relay involved, for instance. Fuses? Fuseable links?

By the way, have you checked that the engine is properly grounded?


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## ghost1 (May 10, 2016)

I am getting 12 volts to both sides of the indicator when switch is in the preheat position only. Voltage goes to zero when key is turned to crank the engine. When twelve volts are present, it still does not glow red. It's the same scenario at the wire coming from harness going to plugs themselves. 12 volts when key is at preheat and zero when engine is cranked for start. Key switch is part number MA-37040820000 which shows unavailable.


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## ghost1 (May 10, 2016)

After looking closely at switch, it has been replaced and the wiring at switch is not matching up to tractor electrical diagram. New switch although having five posts (so does diagram), is only utilizing four. I would disconnect all wiring from switch, however i.d. marks (letters) don't match up to ones on diagram and I'm not sure which wires go where.


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## ghost1 (May 10, 2016)

I disconnected switch and did continuity test from wiring diagram. Switch is not correct for tractor. Does anyone know how to find one that will work since not made anymore?


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## ghost1 (May 10, 2016)

Here is diagram


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## pogobill (Jan 31, 2012)

Something like this may work. Someone may have some way better ideas than I!

https://www.amazon.com/Ignition-Swi...Q67EMYGTVCE&psc=1&refRID=TZ7WD6YV5Q67EMYGTVCE


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## Hacke (Feb 22, 2011)

I found the wiring diagram in Cub-Cadet-7000-Series-Compact-Service-Repair-Manual.pdf at:
https://www.mymowerparts.com/pdf/Cub-Cadet-Service-and-Repair-Manuals/
Attached the wiring diagram.

There are no relay, fuses or other components involved in the heating circuits.

At the key switch:
Black/Yellow wire: Starter motor relay (ST).
Black/White wire: Preheating indicator coil (G1).
Black/Red wire: Glow plugs directly, crank+heat (G2).

On your key switch, the Black/Red and Black/White wires are connected to the same lug. According to the description of your problems, this lug is G1.

There is an unused lug on your key switch, could that be G2? If it has 12 V only when you crank, then it is G2 and if you move the Black/Red wire from G1 to G2, things should work.

If the unused lug is not G2, connect the Black/Red wire together with the Black/Yellow wire on the ST lug. That gives the same result as connecting the Black/Red wire to a proper G2 lug. I can not see a problem with that, but there might be thinner contacts inside the switch for the starter relay and the glow plugs draws a 30A current, so it may be wise to get a proper key switch. But for testing purposes it should work.


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## ghost1 (May 10, 2016)

Thanks Hacke, that info made a lot of sense. The unused lug does not activate when cranked. If I attach wires together on the ST lug, will I loose the preheat function? I would really like to find a correct switch, however, since they no longer exist by part number would you have any suggestions on how to find a suitable replacement? Thanks again.


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## Hacke (Feb 22, 2011)

You will have the preheat function and the crank heat. Since the wires for both preheat and crank heat were connected together, you did not have any current going through the indicator coil at preheating. That resulted in preheating with full voltage, which does not seems to have damaged the plugs, if I understood your measuring right?
No heating when you cranked, since the crank heat wire was at the preheat lug, and that is disconnected when you crank.

The preheat wire (Black/White) stays on the lug where it is, and gives you preheating current through the indicator coil.
The crank heat wire (Black/Red) goes on the ST lug, together with the Black/Yellow wire, and gives you heating current directly, while the starter motor cranks the engine.

I would go for the solution above, but instead of feeding the plugs directly through the key switch while cranking, I would have a relay managing the high current for the plugs and let the Black/Red wire be the control for the relay. A cheap 40 A automotive relay and a piece of wire should do the trick.

Anyhow, connect the wires as suggested and see if the indicator glows when preheating, and if the crank heat works. 
Be careful when you test, these circuits are unfused. Trace the wiring first to make sure it is as in the diagram.

You say that the indicator used to glow, but not anymore. With the wires connected as in the picture, the indicator would not glow. There has to be a reason to why the wiring was changed. A faulty switch is one, but the rerouting of the crank heat wire did not make things better...

A switch like the one pogobill suggested would fill your needs. You could use a more common switch and a separate push button for the preheat.


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## ghost1 (May 10, 2016)

I'm clear on everything except where to place the relay. Should it be coming off the starter switch to where it's activated when key turned for start?


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## Hacke (Feb 22, 2011)

I have been rethinking.
I do not think the idea of connecting the crank heat wire (Black/Red) to the ST lug is safe. Depending on the voltage after the indicator coil it could lead to that the starter motor engages when you preheat, and that is not so good.

I attached an updated diagram with a relay.
With this solution you do not need to cut or splice any wires, everything is kept as original, with some additions.

The crank heat wire will be left disconnected at the switch, isolate the connector thoroughly.

A feed wire is connected to the battery post on the starter motor, and goes to the new relay contact lug.
A wire is connected between the new relay contact lug and the first glow plug (together with the Black/Red wire).
These wires should be at least of the same gauge as the Black/Red wire.

A control wire is connected to the starter motor relay control post, and goes to the new relay control lug.
A ground wire is connected to the new relay ground lug, and goes to ground.


I found this:
https://www.fastline.com/electrical...3-7273-7/39e5ef84-e063-4e2b-995b-bf4ff482f6cf
It has 10.5 V as working voltage. The one I linked to earlier had 7 V. Maybe there are more variants for this engine. That made me think that perhaps a previous owner had put 12 V plugs in it, and that the rewiring was done so the plugs got 12 V when preheating?


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## Bill Rodgers (Dec 14, 2019)

We can supply the proper switch. Go to tractorandtillerparts.com or call 800-609-5110. We are a former Cub Cadet dealer and the oldest Mitsubishi dealer in the country (since 1979). Valley Power Products


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## Ed Williams (Jun 13, 2019)

I could not get my thermal start glow plug to work from the switch. Instead of removing the cowl to replace the ignition switch, I installed a 30A momentary on switch to activate the thermal start. It is just a spring loaded push button. You have to hold it in to activate the glow plug and disconnects the system when you take your thumb off the button. Kind of a pain in cold weather to have to hold the button in, but the self disconnect is nice. Do not have to worry if you left a switch on after the motor starts. I find myself not using the thermal start very much. I have a very flexible rubber hose connection on the intake. I remove the end on the manifold, 10 sec job, and insert my B&D heat gun into the manifold. Wait about 45 sec until the manifold is nicely warm at #3 cyl with cold hands in warm pockets. The tractor fires right up with no ether or messy starting fluids or fire. Rove the heat gun and reattach the hose when it starts. The heat gun is self supported by the manifold and removed hoes end, so no cold hands.


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## Chuck#3 (Jul 18, 2017)

ghost1 said:


> I have a Cub 7235 (Mitsubishi 3 cylinder) and now that the weather is cooling off, it won't start unless I use starting fluid "sparingly" as I'm reading not a good idea with glow plugs. It's getting 9.8 volts to the plugs, however, the glow plug indicator is not lighting up (it's the coil type). Is that enough voltage to plugs and is there a way to test them to see if good?


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## Chuck#3 (Jul 18, 2017)

try turning the ignition on for maybe 10 seconds .
that should make glow plugs heat cylinder. Than crank .may take longer than 10 seconds maybe 15 seconds. Try it out. They may not have wanted to draw juice away from the cranking cycle.


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## ghost1 (May 10, 2016)

WOW! What a great forum. Thanks to everyone for opinions and guidance. Hacke your graphics are professional. I followed instructions and I get power to plugs at start sequence, however, at preheat I'm only getting power to G1 and indicator (which still doesn't glow), but nothing at plugs.


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## Hacke (Feb 22, 2011)

Great, one part of the problem solved.

Now you have an indication (!) of a faulty (broken) indicator coil. You got fooled by the wiring change at the key switch. At that point the coil was fed 12 V at both ends and that made it seem like the coil was connecting when you measured voltage. I do not know what resistance you can expect from it, but if you measure the connectivity it will show open circuit if it is broken.


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## ghost1 (May 10, 2016)

I found the problem. I failed to hook wire coming from G1/indicator back up to the first plug. Everything now working..... Thanks again for taking the time to help me get this fixed......


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## Hacke (Feb 22, 2011)

Excellent! , now it is time to pimp your ride.

When the engine is warm, you do not need the plugs while cranking. You can let the control wire (blue in diagram) from the starter relay make a turn to the dash and back to the new relay, and put a switch on the dash. This way you can disable the plugs when cranking a hot engine, or practically; You can leave it off, and switch it on only when needed.

You can splice a wire to the disconnected Black/Red wire at the key switch, and route the new wire to a light bulb on the dash. The bulb will tell you if there is voltage at the plugs or not, when you crank.

Print out your wiring diagram and save the document for future needs.


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## ghost1 (May 10, 2016)

Thanks again Hacke. I'm sure of the answer, but nothing I would have done would cause the Temp and Fuel gauges to stop working, right? All three fuses in box are good...


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## Hacke (Feb 22, 2011)

I assume that, normally, the gauges, oil pressure warning light and charging warning light goes on when you turn the key to ON?
Are the warning lights working, but not the gauges?
Are the headlights working?
You have been cranking the engine, but does it start and run OK (= fuel solenoid hold have power)?


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## ghost1 (May 10, 2016)

Yes, oil pressure and charging lights work when key is turned on, but gauges do not. Previous owner did away with headlights and I think wires have been disconnected. Engine does start and run normally. I removed cowl underneath gauge panel to check wiring harness and everything seems normal..


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## Hacke (Feb 22, 2011)

There are three possible causes:
Internal fault in the cluster.
Wiring problem.
Sensor problem.

Not very likely sensor problem on both sensors, but check it anyway:
Find the temperature sensor and disconnect the wire.
Connect the end of the wire to good ground.
With the key in ON position, the temperature gauge should react.
If it does, the sensor is bad.
If not, there is a problem with the wiring or/and the cluster.
Most likely the wiring, so check that first.

Check the wiring:
Remove the multi contact from the cluster.
Check continuity between pin 32 (the Yellow/Black wire) and the end of the wire at the temperature sensor.
Easy done with a bulb connected at the sensor end, and 12 V at connector pin 32.
If the bulb does not light, disconnect the other multi connector and apply 12 V at pin 32 (Yellow/Black).
If the bulb lights, the problem is between this connector and the cluster.
If not, the problem is between this connector and the sensor.

Check the cluster:
Find the multi connector at the cluster.
Find a Yellow/Black wire that goes in to the connector (pin 32).
"Back probe" the contact with a needle or a thin pin of some sort. You push it in the connector in parallell with the wire, until the pin gets in contact with the metal parts inside the contact.
Connect the pin to good ground.
Check that everything is connected as normal.
Switch the key to the ON position.
If the temperature gauge reacts, the cluster is good.


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## ghost1 (May 10, 2016)

Everything checked good except for "Check the cluster". Negative results there. I'm ok without a fuel gauge, is there something I can purchase that will substitute for the temp gauge?


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## Hacke (Feb 22, 2011)

I suppose you mean that the temperature sensor test went bad, you did not get any reaction when you grounded the sensor wire?
And you have connectivity all the way from sender to cluster?

I missed the ground connection, are the turn signal arrows, high beam light and illumination light in the cluster working?
If not, check the black wire at pin 0 on the cluster, apply good ground with the "back probe", and watch the fuel gauge.

Of course you can use a third party temperature sender/gauge. I think the test results points to bad connections (solder joints for instance) inside the cluster. Remove the cluster from the tractor, take it apart and examine it.


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## ghost1 (May 10, 2016)

All test are proving negative. Before I dismantle cluster, would I have to replace temp sending unit in block, or would a gauge from an auto parts store attach to existing unit?


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## Hacke (Feb 22, 2011)

I am getting a bit confused, first: "Everything checked good except for 'Check the cluster'.", then: "All tests are proving negative"? 
Did you have connectivity in the wiring, all the way from temperature sender to the multi contact on the cluster?


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## ghost1 (May 10, 2016)

Sorry for the confusion.
1. Disconnected wire at sensor and grounded the wire. With key on, there was no movement at gauge.
2. There is continuity between pin 32 and wire at temperature sensor
3. Back probed pin 32 and connected other end of probe to ground with no effect at gauge.
4. Back probed ground at zero pin of cluster and there was continuity from that pin to a ground on frame
5. Turn signals, horn, and lights have never worked since I purchased machine.


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## Hacke (Feb 22, 2011)

OK, You do not know if the temperature sender is faulty, you only know that the gauge does not work.
I meant that you can of course put a third party temperature sender/gauge kit on the tractor, if you decide that, but the test results points to bad connections, rather than faulty gauges. I would rather try to fix the cluster. If it can be done, your gauges and lights will work.

So, nothing is working in the cluster, except the oil pressure and charging warning lights?
Not even the illumination (back light)?

If you take the cluster apart and examine it, you might be able to find out what is wrong with it. There are probably circuit boards and/or thin strips of metal carrying the current. It can also be a problem with a contact pin/receiver. With the cluster apart you can check the components. If the conductors are covered with some hardened resin, there may be a problem.


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## ghost1 (May 10, 2016)

Nothing on cluster operates except for the oil/charging lights and tach. I will remove the cluster and take a look. My truck had similar issues on its cluster and needed existing solder joints reheated. I'm going to be off line for a couple of weeks, but will advise findings upon return. Thanks Hacke for taking time to help.


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## Hacke (Feb 22, 2011)

That is great, this forum (and a lot more) is filled with postings that do not end with solutions. They are absolutely useless to the readers, because it does not help someone with similar problems, or educate a bit.

If you have the time and possibility, it would be interesting seeing some pictures of the cluster's innards.


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## ghost1 (May 10, 2016)

There are two wires on back of light switch that have come off. Next to the cluster attachment, there is a loose connection on the circuit board that looks fresh.


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## Hacke (Feb 22, 2011)

Thanks for the pictures.
As I understand it:
The gauges, tachometer and a light "matrix" are held in place in the white plastic housing.
The circuit board is screwed on to the gauges and the tachometer.
The four screws that make a rectangle are the screws for the gauges, and they connect electrically between the copper strips and the gauges.

Remove all Phillips head screws.
Remove the light bulbs. The black plastic things are sockets with bulb, you twist and pull them out.
(The missing lights are missing because they have been removed.)
Now you should be able to push the board to the side, away from the white tabs, and remove it.
Remove the tape strips.
Clean the whole surface thoroughly, but carefully, with isopropyl alcohol (rubbing alcohol) and a tooth brush.
Note which wire goes on which pin in the multi connector.
Now you know what goes where, then you can test the gauges properly.
Broken strips can be replaced by a piece of wire, soldered to parts of strips that are OK.

The light switch.
As I understand, the switch is for both lights and turn signals, and the loose wires (Green/Blue and Green/Red) are for the turn signals.
That picture illustrates very clearly why you should not solder connections on a vehicle, at least not on wires that can move.


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## ghost1 (May 10, 2016)

The copper strip on the circuit board was the culprit for the temp gauge not working. I'm sure while removing gauge panel to work on ignition, I rubbed circuit board against something to cause copper strip to break. I attempted to solder a wire to join circuit, but copper foil is so thin I was doing more harm than good. I got one end to adhere and went to the back side of cluster pins to complete connection (pics attached). It's not professional but needle pegs when wire at sensor is grounded.


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## Hacke (Feb 22, 2011)

You could use crimp connectors with suitable eylets for the gauges connections. Remove the screws and clean the strip under it.

Edit ***
And use new screws, brass if you have.
***


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