Idiot light dash to tach dash with lower gauges ?

[PT'S 70 CST]

Ok guys I finally built my buddies tach dash built for his 68 and he has the idiot light dash and wants to covert it to the tach with lower gauges. I have seen the schematic on GMC Pauls web site but I am not an electrician and he has a super nice 68 with a 468 BB in it. This is about a 16-20 k truck and if he wants me to hook up the dash the I sure as hell do not want to mess up his truck. For those of you that have done this before can you tell me any tricks or tips before I tear into his truck.


Thanks PT

[davepl]

I converted a Canadian Pontiac Laurentian idiot-light car over to US Bonneville gauges, and the way I went about it was to get the wiring diagrams for both and compare the differences.

I presume you know you need to change the sensors... idiot light senders for oil and temp are a simple off/on at a certain threshold, whereas the gauge senders are variable resistance. But I would bet that to save costs the wire that carries the off/on signal from the idiot-light sensor is the same one that carries the variable-resistance signal.

Looking at the parts book, however, it looks like they use a different harness with gauges, so you'll need to watch.

[jaros44sr]

Just did this not to long ago, and it seems like the only two wires i added was the black and black/white for the ammeter. I wrote every thing down at the gauge cluster plug and moved things around where they had to be...

I had a whole idiot light harness i bought off our boards and just switched it over, and rewrapped the harness with the two extra wires inside

Might be easier to have the harness out...hope this helps

[lolife99]

Is it possible to just buy the correct under hood harness?
Or do you have to change the under dash harness as well?

[PT'S 70 CST]

Here is what I have found.
http://www.gmcpauls.com/Tech%2520Tips1.htm


PT

[litew8]

you need to fuse them, 4A fuses for both of those wires

[rkn463]

I've never done this on a truck but I did convert a few Olds 442s from idiot lights to gauges and one thing that drove me nuts until I figured it out was that the temp gauge would peg while cranking the engine but was normal when in the run position. I realized that this was a sort of "self test" on the lights, they come on while cranking to let you know the bulb is still good. The gauges dont need that. (no need on the oil pressure because it will be on anyway) Anyway I checked the factory wiring diagram and found the offending wire at the ignition swith and clipped it and then they worked normally. I don't know if the trucks idiot lights had that feature or not. Also the plug on the gauge cluster was the same but the wires were in different positions.

-Richard