Hey guys, converted the 68 cutlass I'm working on to a rally pac set up for the gauges. Originally had the idiot lights. How do I stop the coolant gauge doing it's circuit test when starting the car. When the ignition switch was out I noticed a black wire (think it was black from memory) that becomes grounded when the switch is in the crank position, again from memory the rest of the wires become live at the correct position depending where the key is.

Is the wire that becomes grounded when cranking the one I need to disconnect?

Thanks guys!

 

Yes, that "lamp test" wire that is grounded in the START postion is only used for the HOT light. You can disconnect it or just ignore it. The temp gauge will simply swing to hot when you crank the engine then work normally after that.

 

It's the green wire in the ignition harness behind where you put in the key on the dash. I disconnected my green wire to keep the temp needle from "pinning" every time I started the car. I've HEARD (no proof) that the continual "pinning" can eventually harm the gauge.


Randy C.

 

I did a rally pack conversion years ago and drove the car for years. The gauge pegged every time I started the car, with no ill effects to the gauge.

 

I read the sticky thread at the top of the electrical page with the how to for a 70 car mentioned the green wire, again from memory on this 68 the wire is black so was just making sure.

I can't see it damaging the gauge, the gauge is designed to have the needle go that far, it just never does when the car is in normal operation.

Did the original rally pac cars do the circuit test when starting?

 

I don't think they did. Modern cars flick everything to max, fuel, temp, volts, rpm, speedo, it's fricking unsettling.

 

The ralllye-pac cars did not have the circuit test feature. And it's definitely the green wire, not the black wire, that controls the circuit test feature. This is pretty much true for all GM A-body models at least from '68 through '72. I made the same conversion on my '70 Pontiac GTO, from idiot lights to factory gauges.


I wrote an article about this in the April 2009 issue of Journey With Olds, on page 9 if it can somehow be looked up on the internet. Here is an excerpt from it:


"[In studying] the wiring diagrams in the 1968 Olds chassis service manual for idiot light (page 12-3) and for gauges (page 15-31)...the primary difference...was, on page 12-3 for idiot lights, there is a green wire running from the "ignition starter switch" to the harness that supplies input to the temp warning light...that green wire is completely missing in the diagram on page 15-31 for gauges. Instead, that particular lead from the ignition starter switch goes to ground when gauges are installed.


I extracted the green wire from the connector at the ignition switch in the dash and taped it off so it wouldn't affect anything. Then, I made my own little ground wire (it's black and it even looks "factory" even though it isn't!) and ran it from that [now empty spot] in the ignition wiring harness connector, to ground. Now the temp [gauge] doesn't "peg" [when I start the car] and all the gauges are working perfectly."


It's up to your own taste on this. I just didn't like the temp gauge pegging every time I started the car. I fixed it such that it doesn't do that anymore but left the wire there just in case someone wanted to put it back to factory original someday (saved the idiot lights just in case).


Randy C.

 

Ah ok. So you can't just remove the green wire and that's it. You need to put a wire back in it's place that goes from the ignition switch to ground?

 

I wouldn't worry about the gauge pegging when you crank the engine and keep a functioning idiot light anyway. You are more likely to notice a light coming on than a needle swinging to hot if you're in busy traffic or just let your attention wander from eyeballing the gauges constantly. We all do that from time to time, much as we may not want to admit to it.

Roger.

 

Hey Roger, yes I think I'll just leave it connected, can't see it causing an issue plus saves pulling the dash appart again. The rally pac doesn't have the idiot light for the coolant temp, only lights for the generator and parking brake

 

I suspect the ground is already there. I just added a ground wire so it would be sure to be there.


You really don't have to pull the dash apart to get at the green wire. It's just a matter of disconnecting the green wire from the ignition harness and taping it off so (1) it doesn't touch anything else; and (2) it can be used again if switching back to idiot lights from gauges. The idiot lights for the parking brake and generator are not affected by the removal of the green wire from the ignition harness.


Again, the only reason I did this is so the gauges would operate as originally intended.


Randy C.