1977 -78 Gauge questions

[3x2GTO]

If I change out the oil gauge from mechanical to electric and buy a new 1978 printed circuit, will my 1977 gauges (without tach or clock) work with a 1978 connector and harness?

[kennyw]

The 1977 engine wiring harnesses had the wire for the electrical sending unit but I'm not sure if the cab harness has the correct wiring. You would want to look at the wiring diagrams for those two years and compare them.

[3x2GTO]

Here's what I have: a 1977 K10 that has had a 1978 2wd cab installed, and I'm fairly certain the 1978 cab still has it's original dash wiring harness and the white plastic gauge backing, but has the 77 gauges with 4wd lamp installed in it, (except the mech oil gauge). I checked the pin order on the dash connector, it's correct for a 1978. The gauge backer/ housing and printed circuit are all pretty rough and need replaced. I've seen all the gauges work except the electric oil gauge that the previous owner installed, and the large brake lamp warning at the bottom left of dash bezel. The small brake warning below the fuel gauge works correctly. I'll check the engine harness and see if I can find the wire for the electric gauge, I've got a feeling that the engine harness is the original 1977 one though. Is it possible to re pin the 1978 connector to a 1977 one without cutting or adding wires? Thanks!

[Dead Parrot]

If you are referring to the gauge cluster connector, YES, they physically stayed the same from 73~87 and even the later square Suburbans used the same connector. (found a cluster in a 89? 4WD burb that I have repurposed for my 75 C10). Not installed yet. You can move the pins around on the connector but you will have to match the printed circuit board. If you can find a yard square, the cluster connector is often one of the last things taken. Get a couple spares, one to test on your cluster while on the bench and one for spare pins. Once you figure out how the wires need to be arranged, move the ones in your 77 to match and add any new ones.

Make use of the many wiring diagrams available on the forum.

[kennyw]

You probably have everything to run the 78 cluster then except the cluster housing itself. The 77 housing doesn't have the ability to mount the electric gauge tabs to connect them to the circuit board. If they drilled a hole to run the mechanical oil gauge, they would have likely taken out the mounting holes for the electrical tabs as well. But, post up some pics of what you are working on, it would be easier to see what you have and what is modified.

I would still recommend downloading the wiring diagrams when you look through the wiring to verify the circuits match up at the correct pins at the firewall. You can download them for free on this forum. It is easy to repin the connectors with a small screwdriver to release the lock tab if needed.

[3x2GTO]

Thanks, I'll post some pictures tonight.

[3x2GTO]

Originally Posted by Dead Parrot

If you are referring to the gauge cluster connector, YES, they physically stayed the same from 73~87 and even the later square Suburbans used the same connector. (found a cluster in a 89? 4WD burb that I have repurposed for my 75 C10). Not installed yet. You can move the pins around on the connector but you will have to match the printed circuit board. If you can find a yard square, the cluster connector is often one of the last things taken. Get a couple spares, one to test on your cluster while on the bench and one for spare pins. Once you figure out how the wires need to be arranged, move the ones in your 77 to match and add any new ones.

Make use of the many wiring diagrams available on the forum.

Great ideas, Thanks

[MJN]

There is a decent about of information posted here about the differences between the instrument clusters
https://73-87.com/7387garage/interio...achometers.htm

[3x2GTO]

Here's some pictures of the gauge panel that's in my 77 K10, the printed circuit is stamped # 250 17325, which comes back as a 78-80, and the harness connector is pinned as a 1978. There's a 4wd lamp under the fuel gauge, so I'm guessing these gauges are original to my 77 truck, previous owner did add a non working electric oil gauge, along with a mechanical oil pressure mounted under the dash. I'd like to buy a new backer/housing and 78-80 printed circuit, and use my gauges, also cut and ad a mechanical oil gauge. Is this even possible?

[3x2GTO]

I'm going to keep it all 1978-1980, to match the harness connector, I'll just add an oil gauge. Thanks!

[kennyw]

That is the correct housing for the electric oil gauge. I would hook it up to a sender and test if it works.

GM did some little changes like this as a rolling update during the middle of a production year, so maybe you have a late 77 build and they switched to electric oil by the time your truck was assembled. But it is also just as likely a PO switched something out in the last 40 years as well.