The 1947 - Present Chevrolet & GMC Truck Message Board Network - View Single Post - Instrument cluster swap-lights to gauges

ray_mcavoy · 09-10-2019, 08:13 PM

Yes, it looks like you have the re-pinning of the cluster connector correct.

In trucks with warning light clusters, the engine side of the tan (circuit #31) oil sender wire was left un-used and it simply dead-ends at the firewall bulkhead connector. The engine side of the dark blue (#931) wire connects to the cab side of the tan (#31) wire that runs to the cluster. When changing over to the gauge cluster, you can simply re-pin the cab side of the tan (#31) wire so it joins up with the currently dead-ended tan (#31) wire in the engine harness. I believe that will involve extracting the wire/terminal from cavity "AW" of the bulkhead connector behind the fuse block and re-locating it to cavity "BX".

The brown (#25) wire is not used for the voltmeter. The voltmeter receives power via one of the pink/black (#39) wires ... the one going to cavity #4 on the cluster plug if I remember correctly. And the voltmeter grounds via one of the black (#150) wires ... cavity #3 on the cluster plug I think.

Yes, you do have to add a resistor to the brown (#25) wire for proper alternator operation. In trucks with factory gauge clusters, GM used a length of resistance wire that's about 10Ω and rated at just over 6 Watts. A 10Ω, 10 Watt resistor should be commonly available at many electronics suppliers. Or, I believe the 10/12SI alternators will work correctly with up to around 150Ω or so, allowing you to use a lower wattage resistor. And if using a newer CS alternator you'll want a minimum of 35Ω in the circuit. You could even wire in a #194 bulb and still have a "GEN" light along with the voltmeter.

The pink #30 fuel sending unit wire doesn't have to go to both cavities #7 and #18 on the cluster connector. The connection to cavity #7 is only needed if you are installing a factory tach cluster that has the small fuel gauge down in the lower left corner. All other clusters use the cavity #18 connection.

Finally, you might want to consider removing the "bulb check" wire from the "temp" light circuit. To do that, simply locate the dark green wire (a branch of circuit #35) on the ignition switch connector and cut it (or extract it terminal & all) and insulate the end. Not doing this will cause the temperature gauge peg full hot while cranking the engine. That's because the ignition switch has a set of contacts that ground this circuit in the "start" position. With the "temp" light, it caused the bulb to light up so the driver would know the bulb was okay.

09-10-2019, 08:13 PM	#3
ray_mcavoy Registered User Join Date: Nov 2009 Location: Sherman, ME Posts: 2,354	Re: Instrument cluster swap-lights to gauges Yes, it looks like you have the re-pinning of the cluster connector correct. In trucks with warning light clusters, the engine side of the tan (circuit #31) oil sender wire was left un-used and it simply dead-ends at the firewall bulkhead connector. The engine side of the dark blue (#931) wire connects to the cab side of the tan (#31) wire that runs to the cluster. When changing over to the gauge cluster, you can simply re-pin the cab side of the tan (#31) wire so it joins up with the currently dead-ended tan (#31) wire in the engine harness. I believe that will involve extracting the wire/terminal from cavity "AW" of the bulkhead connector behind the fuse block and re-locating it to cavity "BX". The brown (#25) wire is not used for the voltmeter. The voltmeter receives power via one of the pink/black (#39) wires ... the one going to cavity #4 on the cluster plug if I remember correctly. And the voltmeter grounds via one of the black (#150) wires ... cavity #3 on the cluster plug I think. Yes, you do have to add a resistor to the brown (#25) wire for proper alternator operation. In trucks with factory gauge clusters, GM used a length of resistance wire that's about 10Ω and rated at just over 6 Watts. A 10Ω, 10 Watt resistor should be commonly available at many electronics suppliers. Or, I believe the 10/12SI alternators will work correctly with up to around 150Ω or so, allowing you to use a lower wattage resistor. And if using a newer CS alternator you'll want a minimum of 35Ω in the circuit. You could even wire in a #194 bulb and still have a "GEN" light along with the voltmeter. The pink #30 fuel sending unit wire doesn't have to go to both cavities #7 and #18 on the cluster connector. The connection to cavity #7 is only needed if you are installing a factory tach cluster that has the small fuel gauge down in the lower left corner. All other clusters use the cavity #18 connection. Finally, you might want to consider removing the "bulb check" wire from the "temp" light circuit. To do that, simply locate the dark green wire (a branch of circuit #35) on the ignition switch connector and cut it (or extract it terminal & all) and insulate the end. Not doing this will cause the temperature gauge peg full hot while cranking the engine. That's because the ignition switch has a set of contacts that ground this circuit in the "start" position. With the "temp" light, it caused the bulb to light up so the driver would know the bulb was okay.