Large to small fuel gauge

[sixshooter798]

I'm sure this has been posted 800 million times, but the search engine didn't yield promising results.

I'm going to swap out my gauge cluster for one with a tach in it, so I'll be going from the large fuel gauge to the small one. Will I need to re-pin the plug that goes into the back of the cluster?

[ray_mcavoy]

Hi sixshooter798,

I didn't have to re-pin the cluster plug when I swapped a tach cluster into dad's 77. His truck already had the factory gauge package (minus the tach) so all I had to do was add the separate harness for the tach.

Before making the swap, I looked at the factory wiring diagrams and it looks like they already took the fuel gauge difference into account. The cluster plug already has two terminals each wired up to the fuel gauge & brake warning light. One pair of terminals is unused by the non-tach gauge cluster while the other pair is unused by the tach cluster.

Note that if you're dealing with a truck that had an idiot light cluster from the factory, you will have to re-pin the connector (and maybe make some wiring changes) to install a full-gauge cluster.

And you might have to do some re-pinning and/or other changes if you're installing a tach cluster out of a medium duty truck. The ones with the small fuel gauge directly below the tach.

Wiring changes will also be necessary if you're using a cluster from a different year range than your truck. For example, 73-75 = ammeter, 76-up = voltmeter. And 73-77 = mechanical oil gauge, 78-up = electric oil gauge.

[sixshooter798]

Cool thanks for the info!

[motornut]

i changed from idiots to gauges/tach
just a couple of wires for yours
notes in my 78 jimmy tread below
see notes on the power and adding grounds.....
i powered my tach from the cluster power

[Evil Trailblazer SS]

As long as your truck had all the small gauges (Oil Pressure, Water Temp, Voltage) your wiring will not have to be re-pinned...

Motornut has a great write-up. The tach wiring harness is simple to wire in, tapp the 12v for the tach gauge off one of the pink/black ingtion 12v wires in the existing cluster harness. Tap the ground to one of the black grounds in the same cluster wiring harness. Run a wire from the Tach Signal on the tach gauge to the distributor. All HEI distributors have a terminal marked "Tach" and all external coils have a wire from the gray plug (Small white wire in same plug as large pink coil wire).

[texastruckjunky]

You see thats why this site is so bad A**, so much usefull information. Thats good to know, now i can put my tack in my blazer. So the tack cluster out of a 78 blazer will work in my 79 blazer? I got every thing even the engine wireing harness.

[motornut]

Originally Posted by texastruckjunky

You see thats why this site is so bad A**, so much usefull information. Thats good to know, now i can put my tack in my blazer. So the tack cluster out of a 78 blazer will work in my 79 blazer? I got every thing even the engine wireing harness.

yup it will...good luck,have you considered painting the inside it sure helped mine

[texastruckjunky]

Yea, thats the plan. I'll get some pics when i get it done, to show everybody how it turns out.