Originally Posted by t5noel (Post 6999246)

I have a gauge cluster now. Is re-pinning necessary when replacing it with a gauge cluster? On second thought is re-pinning necessary for changing over from ammeter to voltage meter?

Originally Posted by gmachinz (Post 6999282)

Yes because the dash harness plug-in is different through the years.

Originally Posted by ray_mcavoy (Post 6999474)

I agree!

Since your 74 is wired for a factory gauge cluster with an ammeter, only a 73 - 75 gauge cluster will be a direct plug-in swap.

A 76 or 77 gauge cluster (with a mechanical oil gauge & voltmeter) would be relatively easy to adapt ... you'd only have to change a couple wires to switch from an ammeter to the voltmeter. And in some cases a wire for the brake warning light.

More significant changes were made to the cluster plug pin-out when these clusters were changed over to electric oil pressure gauges.

Originally Posted by hatzie (Post 7000982)

One thing I failed to mention is the fact that the later clusters have electric oil pressure senders while your 74 has a Bourdon Tube oil pressure gauge with a copper line running through the firewall to the engine.
If you were moving from warning lamps to gauges you would already have an oil pressure sender wire. You have gauges so you'll have to route an oil pressure sender wire. You can likely utilize the open oil warning switch/lamp Circuit #31 spot in the bulkhead plug with Delphi Packard 56 male and female terminals on SXL wire. That spot should be unused on your gauge cluster truck. If you want to be "correct" about it use Dark Blue wire.
The 8900371 instrument cluster plug is obsolete and likely the terminals are as well. A terminal and wire pigtail will need to be salvaged from a 73-87 GM truck.

Originally Posted by hatzie (Post 7000982)

One thing I failed to mention is the fact that the later clusters have electric oil pressure senders ..... so you'll have to route an oil pressure sender wire.

Originally Posted by t5noel (Post 7002307)

I've examined the difference between the two. There will be two additional ground wires and one additional power wire. Can I splice the added ground wires from the one ground? I would assume the added fused power would have to come from the fuse box.

Originally Posted by t5noel (Post 7002307)

There are two wires for the fuel sender. Is the second for dual tanks? Can it be left out if so?

Originally Posted by ray_mcavoy (Post 7002335)

Yes, the additional ground wires can be spliced into the existing circuit #150 ground wire(s) already leading to the cluster plug.

The same goes for the additional ignition-switched fused power wire. That can be spliced into one of the existing circuit #39 power wire(s) already leading to the cluster.



The two fuel sender wires allowed the factory gauge wiring to accept gauge clusters with or without the optional tachometer.

The fuel sender wire leading to cavity #18 is used for clusters with the large fuel gauge located to the right of the speedometer. I believe it's also used for medium-duty truck tach clusters with the small fuel gauge at the bottom of the tach.

The fuel sender wire leading to cavity #7 is only used for tachometer clusters that have the small fuel gauge down in the lower left corner.

So depending on the style of cluster you're installing, only one of the 2 wires for the fuel sender will actually be used. I suppose you could remove the extra one but leaving it in there won't hurt anything ... the unused one just dead-ends at the cluster plug since there is no mating trace on the printed circuit.

Originally Posted by t5noel (Post 7002382)

Is there any trick to pulling the pins from the plug or is it pretty straight forward?

Originally Posted by t5noel (Post 6999215)

Can anyone tell me if these instrument clusters are compatible with a 1974 GMC pickup?

Originally Posted by Gregski (Post 7004691)

Hi Noel?

I am in the exact same boat [ahem] truck, also a '74 GMC looking for a Tach / small fuel gauge cluster, I have not seen any at the 4 local junkyards I frequent though, and eBay prices are redunculous, have you seen the guy asking $500 bucks for an OEM Tachometer yet?