# Glow plug indicator



## ghost1 (May 10, 2016)

I recently purchased a Cub Cadet 7235 and have a question about the glow plug indicator on dash. I've seen it glow red but now there's nothing. The wiring diagram doesn't show a relay and if I'm reading it correctly, it's not fused. Battery is at 12 volts, however, when I turn key to the left to activate glow plugs, there's no voltage on either side of indicator.


----------



## ghost1 (May 10, 2016)

Checked voltage at indicator and it's reading 9 volts. I hooked it directly to battery and it glows red. Glow plugs are getting 9 volts also


----------



## Groo (Jan 17, 2020)

Maybe a key switch contact fried?

Why only 9v? Is it a 9v system?


----------



## ghost1 (May 10, 2016)

I think you're on to something about the switch. I'm getting 12 volts to switch, but when I activate indicator, I'm only getting 9 volts to it and it's a direct wire from switch to indicator pole.


----------



## ghost1 (May 10, 2016)

Part number is MA-37040820000 which is no longer made. Does anyone know what would be a replacement?


----------



## Groo (Jan 17, 2020)

Just a pushbutton contact switch would do it, or probably any "modern" ignition switch with glow plug support.


----------



## ghost1 (May 10, 2016)

Thanks Groo. Electronics not my strong suit. If I use a push button switch, do I go from battery to switch to indicator to glow plugs and the ground would be the glow plugs screwed into block?


----------



## Groo (Jan 17, 2020)

Looks like those glow plugs are not rated for 12v, only 10.5v from what I saw.
I don't know if the indicator is enough to drop the voltage or not.
the other thought is that the glow plugs are cheap, so no huge deal if they burn up, assuming they are easily accessible.


----------



## marc_hanna (Apr 10, 2017)

If you're wiring up something new, you typically want to isolate the switch from the full current. You could use a simple solid state relay rated for the proper current. These are only a few dollars. That will allow you to use a small discrete switch or button with no risk of burning it up and getting a shock.

I suspect you have a bad relay though. The key switch and/or the wiring could be bad also.


----------



## Groo (Jan 17, 2020)

marc_hanna said:


> If you're wiring up something new, you typically want to isolate the switch from the full current. You could use a simple solid state relay rated for the proper current. These are only a few dollars. That will allow you to use a small discrete switch or button with no risk of burning it up and getting a shock.
> 
> I suspect you have a bad relay though. The key switch and/or the wiring could be bad also.


Depends on the current and what the switch is rated for. If there was no relay before, its probably not needed. If there was a relay before, that is probably what failed.


----------



## marc_hanna (Apr 10, 2017)

Groo said:


> Depends on the current and what the switch is rated for. If there was no relay before, its probably not needed. If there was a relay before, that is probably what failed.


Agreed, but the very nature of a glowplug requires a good amount of current, definitely more than you want running through the indicator light. I suspect there is a relay there somewhere.


----------



## ghost1 (May 10, 2016)

Thanks all. I will look for a relay


----------



## Groo (Jan 17, 2020)

marc_hanna said:


> Agreed, but the very nature of a glowplug requires a good amount of current, definitely more than you want running through the indicator light. I suspect there is a relay there somewhere.


the glow plug indicator on the old Kubota was a fairly heavy solid wire. It wasn't a light bulb.


----------



## ghost1 (May 10, 2016)

I'm attaching a schematic if it might mean something to somebody.


----------



## Groo (Jan 17, 2020)

no relay. No replaceable fuse either. There is a fusible link there, so not entirely unfused. that fusible link also energizes the starter relay and the accessories, so that isn't the problem.

looks like the glow plugs get reduced power through the indicator (indicator will act as a resistor) when pre-heating, then full power when cranking.

if you have an open loop when testing resistance through the indicator, that is the problem. Otherwise, it is likely the switch, as you initially thought.

Put a high amp rated push button from G1 to B if it is the switch that is the problem.


----------



## ghost1 (May 10, 2016)

Thanks Groo. Do you know what a good resistance through the indicator would be? I just ran a continuity test.


----------



## Groo (Jan 17, 2020)

it would significantly be less than the resistance of a glow plug, but of the same general order.
so if a single glow plug was 2 ohms, I would expect the resistance from the indicator to be more like 1/4 ohm. really pulling numbers of my hind end here, but you get the idea.

its not going to be thousands of ohms because that wouldn't let any real current through. If you have 12v, you needs 1 ohm to get 12 amps. resistance in series is added. resistance in parallel is the reciprocal of the added reciprocals, or something like that. its been a few decades.

one other thing to consider is that the resistance of the indicator or the glow plug might rise as they heat up, so even what I said might be completely wrong.

basically, I don't have a real answer for you, but as long as its not shorted or open(or very high at all), is should be fine.


----------

