Instrument cluster swap-lights to gauges

[1967KaiserM715]

Hoping to get some help before I completely screw up. I have a 1986 GMC C30 wiring harness, both engine and cab side. It is going in a 1986 Chevy K30. Neither truck had gauges, only Idiot lights. plus the wiring harness on the K30 was completely hacked, not worth my time to rewire, especially since the C30 harness was complete and matched the engine I am installing.

Engine is a 292(4.8L) inline, with HEI, manual choke 2 barrel Holley.

On the C30 engine side harness, I removed the choke wiring, AIR and associated wiring(I did leave short sections of wire, all taped/heat shrinked to avoid shorts). I left the oil pressure, coolant temp, alternator and starter wiring.

In the cab, and the real issue, is converting the stock idiot light dash wiring to stock gauge wiring. As I have it now-number slot on plug, circuit number, wire color.

1,11, light green.......18,30,pink
2,8,grey..................17,-,-
3,31,tan..................16,237,yellow
4,35,dark green.........15,150,black
5,39,pink/black..........14,-,-
6,50,brown...............13,-,-
7,25,brown...............12,39,pink/black
8,33,tan/white..........11,15,dark blue
9,150,black..............10,14,light blue

and then how it needs to be wired, and colors as listed on wiring diagrams.

1,11, light green........18,30,pink
2,8,grey...................17,33,tan/white
3,150,black...............16,39,pink/black
4,39,pink/black..........15,931,dark blue
5,31,tan...................14,-,-
6,39,pink/black..........13,237,yellow
7,30,pink..................12,15,dark blue
8,150,black...............11,14,light blue
9,35,dark green.........10,150,black

I am pretty sure I don't need to worry about slot 15,931,dark blue as that should be the choke indicator. But according to the wiring diagram, #31 on the engine side is tan for oil pressure, but I don't think it is the same #31 on the cab side for idiot lights. Do I need to splice into the bulkhead connector to add this circuit? OR should I splice the engine side and move the oil pressure tan #31 to choke dark blue #931, which means I can use the cab side #31 tan as the oil pressure gauge wire.

and Brown #25 for idiot lights is not used-but what will be used for the volt meter? and I think I need to add a resistor to Brown #25 for proper alternator charge??

I think the rest is self explanatory I need to add 1 ground(150, black), slot 7, #30 pink can be spliced from slot 18, #30. and one extra splice to #39, Pink/black.

[Palf70Step]

This is what I used when setting up my truck. Mine is 81, but I think it is pretty much the same.

The choke Light/second oil pressure sensor (to turn choke power on/off), you probably don't need.

The volt meter can pretty much tap any switched 12V source to get a proper reading. I know you'll need to add a diode or resistor or both to replace the voltage lamp, I just don't remember what you need.
As you mentioned the tan wire is for the actual oil pressure gauge sender.

[ray_mcavoy]

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.

[1967KaiserM715]

Perfect, thank you both.