How To Wire a Tachometer?
 

I was searching Craigslist the other day and came across a factory tachometer & fuel gauge combo unit out of a 1975 1 ton truck. I thought it was a good deal for $20 because it came with the factory wiring harness so I bought it. My problem is am I missing part of the wiring harness and do trucks produced without the factory tach/fuel gauge still wired for a factory tach/fuel gauge? Meaning is the wiring harness the same for all trucks with or without the factory tach/fuel gauge? I'm putting this in a 1973 Chevy C20 454 and can't figure out where the 3 individual wires go that are pictured below?

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Re: How To Wire a Tachometer?
 

I can't remember for sure,just got the one in my crew working about a month or so ago.The one with the ring is probably ground & pretty sure the white gies to the tach terminal on the dizzy.The third is your power wire.Someone else might be able to confrm this.

Re: How To Wire a Tachometer?
 

Awesome find! Like the poster below the ring is ground I believe. But I'm pretty sure the pink(white?) would be your power and the other black with the quick connect would be your distributer if I can remember correctly.

Re: How To Wire a Tachometer?
 

If you look closely at the white plastic plate on the back of the tach, you'll see that it has the tachometer connections labeled. They are:

+12V ... should be a pink wire that plugs into an "IGN" terminal on the fusebox.
GND ... should be a black wire that clips onto the metal part of the dash (or plugs into the ground buss near the parking brake on 78+ trucks).
COIL ... should be a brown wire (or white on later year harnesses) that runs through a grommet in the firewall and connects to the negative side of the coil (if you have points) or connects to the "TACH" terminal (if you have HEI).

If you are installing that tach/fuel gauge combo into a non-tach cluster, you will have to make some modifications to the plastic cluster housing to make it fit. And the traces on the printed circuit won't line up with the fuel gauge in it's lower position so you'll have to add some short jumper wires or something to extend them to reach.

Re: How To Wire a Tachometer?
 

I was just wondering how to install it in the factory fuel gauge place because the combo unit won't fit. I think I need to cut the back out of the instrument cluster itself?

Re: How To Wire a Tachometer?
 

There are several variations of the gauge cluster layout as you have probably figured out. In most cases you will need to change the flex circuit to accommodate the tach in place of the fuel gauge. Over the years I have collected many spare parts including some extra flex circuits and the tach wiring harness. Send me an IM and I would be glad to swap around some parts for you.

Re: How To Wire a Tachometer?
 

Swap around which parts? I got it wired up, sometimes I just need to figure it out on my own before asking questions because it's usually simpler than I first thought. The gauge cluster housing plastic is about as worthless as my ex-wife, just barely touch it and it falls apart, lol. I also had to solder some wires that extend down about 2"s to the new fuel gauge. Everything works good, no complaints!