Tach wire termination if no tach

[rich weyand]

Does anybody know where the brown tach wire terminates under the dash if you do not have a tach on the truck?

I am buying the combo tach/fuel gauge from these guys, and would like to have some idea of where to look for the other end of that wire. It is there, it comes off the distributor and heads into the cab, I just don't know where it ends up. Yet.

http://www.gmsports.com/content/new-...and-gmc-trucks

[TBONE1964]

You should have a loose connector under your dash if your truck originally came with a tach. It will be a connector with three terminals that plug into the back of the tach directly. You should have 12V power, ground and tach (brown wire to coil).

If your truck did not come factory with a tach, the factory tach harness would not be there. If there was an aftermarket tach, the wire to the coil is usually green.

You should be able to purchase a tach wiring harness for your truck if needed.

[ray_mcavoy]

I agree with TBONE1964 ... it should lead back to a 3-terminal connector under the dash if your truck originally had a factory tach.

There were a few other factory systems (besides tachometers) that sometimes plugged into the HEI tach terminal though.

Like the ECM on some electronic feedback carburetor systems for example. And some engines had the idle speed solenoid on the carb wired into a "speed switch" that had a wire plugged into the HEI tach terminal. That was primarily on mid 80's 1-ton trucks though (and they'd changed from a brown to a white tach wire by then) ... here's a diagram of that setup that also shows how a factory tach would tie into that system:

[TBONE1964]

Originally Posted by ray_mcavoy

I agree with TBONE1964 ... it should lead back to a 3-terminal connector under the dash if your truck originally had a factory tach.

There were a few other factory systems (besides tachometers) that sometimes plugged into the HEI tach terminal though.

Like the ECM on some electronic feedback carburetor systems for example. And some engines had the idle speed solenoid on the carb wired into a "speed switch" that had a wire plugged into the HEI tach terminal. That was primarily on mid 80's 1-ton trucks though (and they'd changed from a brown to a white tach wire by then) ... here's a diagram of that setup that also shows how a factory tach would tie into that system:

Good points Ray, I did not think of the non tach related terminals that use that location.

[J Knight]

Originally Posted by rich weyand

Does anybody know where the brown tach wire terminates under the dash if you do not have a tach on the truck?

I am buying the combo tach/fuel gauge from these guys, and would like to have some idea of where to look for the other end of that wire. It is there, it comes off the distributor and heads into the cab, I just don't know where it ends up. Yet.

http://www.gmsports.com/content/new-...and-gmc-trucks

I have this same aftermarket tach. You don't need any of the wiring under the dash. It is plug and play and comes with a single wire that plugs into the back of the tach that goes through the firewall and plugs into the tach lead on the distributor. The tach itself plugs into the same power leads the original fuel gauge did.

[TBONE1964]

Well there you have it. Right from someone who did the exact same thing.

Good information here

[rich weyand]

No tach on it now, and far as I know, there never was, but there is the brown wire there. Wondered if it would be easier to patch into that than run the wire provided with the gauge all the way to the distributor.

It's really cool that the combo gauge plugs right into the basket. The original combo gauge that they used on the medium trucks in the seventies had the fuel gauge terminals lower, so you have to cobble that in. This aftermarket gauge was constructed specifically to be plug-and-play in our trucks by this seller. They tell me they sell a lot of them.

Thanks everybody. This should go in quick -- other than disassembling the instrument panel yet again. <sigh>