1972 gmc tach wire

[jd hauler]

does anyone know which wire runs the tach? I have an unhooked yellow wire out under the hood, with a spade connector, but want to make sure, and does anyone know how the backlighting for the tach works? I dont see any bulbs with the twist in socket for the tach? thanks In advance.

[ETsC10]

Looks like you need a boost to the top.....ttt!

[JimKshortstep4x4]

The existing bulbs on either side of the tach provides light for it. Factory tach wires are not yellow. I suspect that it could be for an emissions system. Where is the wire located?

Jim

[70cst]

Here you go jd hauler ... a bump to the top.

By the way and from Ohio...

[LockDoc]

-
The original tach wires are Red & Brown. Red to power (ignition unfused on the fuse panel) and Brown to negative side of coil or "TACH" terminal on distributor.

LockDoc

[jd hauler]

ok, thanks , one more wire question, I have a heavy black wire that comes out of my steering column with a soldered on brass terminal, the truck had cruise , as it still has the button, now I have a diesel motor in it. would this have been the wire for that, or did the shift indicator have backlighting? any chance this cruise could still be used for the 6.2 diesel?

[jd hauler]

the yellow wire is to the left of the air cleaner looking at the motor, up in the wire tray, any idea what that is for?

[Longhorn Man]

the black wire in the column isn't a wire, but a fiberoptic cable that lights the shift indicator. It's supposed to plug into one of the twist in bulb holders on the inst panel.
The yellow wire on the passneger side of the motor probably goes down to the starter. I suspect your truck has been updated with an HEI system and no longer needs that yellow wire. If this is the case, you can cut it out.

[jd hauler]

I gotcha, I was wondering how that worked because of no ground wire and didnt see any type of bulb in the indicator, and yes I now have a 6.2 diesel living in the old truck, thanks for your help. any chance of getting the fiber cable to work? I dont know if I ever will, do you know where its suppose to plug in, or could it be fed from any light?

[05crewcab]

Welcome!


You are going to have to figure out a different way to run the tach, or perhaps you can't run it at all with the diesel. There is no distributor, coil, HEI, etc. to hook a wire up to.

I have no idea how to run a factory tach with a 6.2, but I am sure someone will chime in.

The fiber optic cable uses a special bulb connector in the instrument panel. it is white, and the rest are black. if I recall, it is on the left side by the speedometer.

[jd hauler]

I saw some tach converters on ebay, one guy told me to tap my center diode and run a wire outside the alternator and then to the converter and then to the tach, at least I found the red and brown tach wires, I did see that white bulb holder and had no idea at the time what that was for, not sure I want to dismantle the dash again, might just run my own wire and light bulb.