1985 Glow plug relay wire question

[rodman68]

I have a 1985 that has sit for some time it started good when I got it but needed some other work on the truck so it sat some time until I got back to it. I remembered when I started it the son said something about some smoke well I figured it out today. They installed a glow plug bypass and I noticed the black wire was melted pretty good. I moved these wires around a long time ago replacing the main battery cables and such so I am not sure what those were attached to maybe they were incorrect at that time. Looking at the relay the purple wire should be on the S terminal of the relay this goes to the manual switch, and the burnt black wires goes to the I terminal? What I can tell this is a ground, odd thing is I found some pictures on controller bypasses and there was no black wire. If its a ground why doesn’t it just go to the frame, and there is a ground that attaches to the base of the glow plug relay. Does that black wire need to be there?

 

[OLDBULL8]

The GP relay has an internal ground to the base. The Purple wire is/was to the WTS lite, evidently it is used to trigger the GP relay in place of the RED key switch wire, it should be connected to the terminal on the relay and is also jumpered to the WTS lite, the WTS lite has it's own ground in the Cab.

The Red, Yellow, Green, Black, White wires are no longer used for a manual trigger of the GP relay, disconnect all of them.

The GP circuit below is how a normal GP controller is hooked up.

I think your controller might be burned up, but you could hook it up and try it, if you want to go back to an auto GP controlling.

 

[madpogue]

OP has an '85, the controller is separate from the relay and the relay is NOT case-grounded. GLOW PLUG light, not a WTS light. I don't remember the wire colors, but here's how the relay should be wired:

* One big terminal - direct from battery+ or from starter relay ('85 EVTM actually routes from battery+ --> GPR big terminal --> starter relay; my truck was re-routed to match the later trucks, i.e. battery+ --> starter relay --> GPR; YMMV)
* Other big terminal - big wires going to the GPs, small wire going to GLOW PLUG light
* One small terminal - trigger wire from GP controller
* Other small terminal - trigger circuit ground (should go to ground ring terminal on fender)

Come to think of it, if you have a GPR with terminals marked S, I, etc, it sounds like someone tried to use a starter relay as a GP relay. FAIL! Starter relay is NOT rated for the current draw of the GPs. This, er, might explain the smoke.

 

[rodman68]

Ok that could explain the smoke it was the small black wire that got hot for sure. So does the 12volts jumper across from the S terminal to the I terminal when power is applied to it? The previous owner said they replaced the glow plug relay not surprised if its incorrect. Can I just use the S connection and it will use the frame ground?

 

[madpogue]

Just get the right relay. If you want way more capacity than you need, get a Western Plow 56131K, $15-20 online. PSD folks use it, and those GPs collectively run aprx. 100 amperes for up to two minutes.

 

[rodman68]

Looked at a new relay from the store and it has the same S and I on it so not sure maybe it is the correct relay. I am going to see if there is a part number to reference to.

 

[madpogue]

The S and I terminals are both "small" terminals, right?

Do a continuity or ohm check, see if either the S or I terminal has continuity with the mounting base. If one of them does, make sure the OTHER terminal is the one connected to the controller. Alternately, try connecting it up, but DON'T mount it, and make sure the relay base is NOT touching any metal (set it on a piece of wood or something). If it works normally that way, then the relay is good (although a heavier duty relay would probably be preferable), and it's the case grounding that's causing the trouble (from getting the S and I terminals switched 'round).