Diesel glow-plug wiring

[lumphammer]

Due to a dodgy ignition switch that I have to operate with a screwdriver, I want to re-do my engine control panel, especially the start and preheat switches to use relays to switch the currents so that I can use lower rating switches on the panel and reduce the volt-drops for the glow plugs.

At the moment the pre-heat wire goes through a small piece of bare copper? mounted just behind a small grill on the front panel before going to the two glo-plugs. I plan to use a high current relay linked directly to the starter moter battery terminal to supply the glow plugs, but I am a bit concerned about what the copper wire on the control panel is. I assume it is some form of limiting resistor to reduce in-rush current, but does anyone have any better ideas.



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[William_H]

Just a wild guess but could this piece of copper have a contact on one end and could it in fact be a time out type device using bimetal strip which bends with heating to open the circuit when the time is up and glo plugs are hot? If so you will need to introduce it into your new circuit to the glo plugs or make some other electronic timer. regards will

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[lumphammer]

I didn't think of that possibility, although I would think it is unlikely as it is in series with the lead to the glo-plugs and I would have thought there should be some interconnection with the starter switch to be of any use.

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[Rick]

I think Will has it - I've seen similar, and there isn't any starting connection - it just causes the glow plugs to activate for a few seconds. When the light goes out, hit the starter type system.

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[seaboy]

If your electrical circuit is 12v, would it be easier to fit a electronic glow plug relay/timer as used on cars (black box). The ones used on such as Ford and Peugeot diesels, which the plug glows for a period of time according to the air temperature (short in summer and long in winter).

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[Bejasus]

This is exactly what I have just done when fitting a 1.8 Ford XLD.

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[MedMan]

The 'small piece of copper' is an essential part of the system. It has the same resistance as each of the glow plugs and, as you say, is wired in series with them. It has two functions:

It gives a visual indication as to what is happening to the glow plugs. You should find it gradually heats up and, after about 15 - 20 seconds, it starts to glow red hot. That is what is happening to each glow plug at the same time. As soon as it starts to glow red hot you can start the engine.

Being wired in series it reduces the voltage to each glow plug to the correct figure. If you removed it, the voltage to each glow plug would rise and they would burn out.

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