# 434 heater circuit



## bobcube (Nov 13, 2014)

I've been trying to get the glow plug circuit working on my 434. I'm a bit stumped how the circuit works and hope someone can de-mystify.

The bit I can't fathom is that the wiring diagram shows two wires from two terminals on the the ignition switch, each wire going to one or other side of the heater indicator.

My understanding is that current should travel through the heater resistor on to the glow plugs, so, what's the purpose of the wire to the other side of the heater indicator for? This would seem to just short out the indicator?
In other respects the glow plugs and heater indicator all check out as OK.



Cheers

Bob


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## FredM (Nov 18, 2015)

can you attach the wiring diagram so we can have a look at this ?.

I would have thought that the glow plugs would use full current, but I can't really comment until I see the wiring diagram.


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## bobcube (Nov 13, 2014)

Hi

I've attached the IH parts manual- I hope that has worked! The wiring schematic is in section 3. The resistor indicator is item 85.

Bob


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## sixbales (May 18, 2011)

Howdy Bob,

The glow plugs are on a common bus and resistor indicator is wired in series with the glow plug bus. If the resistor indicator is open circuit, the glow plugs will not work.

It appears to me that when you put the switch in the "preheat" position, power is supplied through terminal 3 of the switch. If everything is working, the resistor indicator light will be "on". 

When you go to the cranking position, the resistor indicator is bypassed to maintain power to the glow plugs (the starter drops the battery voltage due to load). The resistor indicator will go "off".

That's my GUESS as to how your system is supposed to work. In one of your earlier posts, you stated that you have the wrong key switch, so it's anybody's guess how it is wired up at this moment.

Hope this makes sense to you. If not post back.


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## bobcube (Nov 13, 2014)

Aha, that makes sense!
I've checked out the ignition switch with a multimeter, and there's an 'inbetween' setting, which, I suspect activates the heater circuit. Continuing turning the key fully clockwise presumably kicks in the starter motor, while shorting out the heater.
A previous owner wired this up wrongly, probably because the wrong ignition switch has been installed. 
I've by-passed some of the wiring and... blow me down... the heater and glow plugs actually work! I can now start the tractor without having to crank for minutes in the cruel British winter....

Next job - get the temp gauge working ...


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## DoubleChevron (Aug 6, 2020)

Hilarious .... I've just been googling exactly the same thing .... Were they on drugs when they wired these things? I dragged out an owners manual to find someone else has already drawn over it (as it doesn't make sense).

I'm not sure if you ever figured it out .... Mine work, but the switch has gone iffy and isn't always shutting off the glow plugs. What you do is switch the ignition on (don't worry about dash lights, they don't matter), then *push on the key and hold it in ....)*. Wait for the glow plug indicator (which is a 5th glow plug) to start glowing then if its cold .... wait about 60seconds and kit the starter...... You fingers will probably be good and sore by the time its ready to start 

I'm just going to remove that weird wiring (that I can't make sense of) and just wire the glowplug indicator into series with a new ignition switch.


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