wiring help needed for fuel gauge and haz lights

[CGT80]

I have a 79 C20 with dual fuel tanks. It had full gauges except for the tachometer. I am cleaning up some wiring so I can get the engine and trans put back in. The fuel gauge sender wire runs from the passenger side frame rail, up past the starter and through the fuse block connector. The wire is really beat up. Since I have dual fuel tanks, the wire that this connects to, near the tanks, is actually run from the fuel switch in the dash. Yep, it makes a big loop. The original wire was used for a single tank and for a dual setup they just added a separate harness. I have wires from each tank sending unit to the switch at the dash.

I am going to run a wire from the tank switch in the dash to my gauges and bypass the wiring outside that runs from the fuse block. I have autometer gauges. I cut wires from the original gauges and tied in with the autometer stuff. It looks like #18 with two small pink wires (at the original gauge plug) is the sensor wire to my gauge. Both pink wires seem to run down to the fuse panel. I don't understand why there are two. My fuel gauge worked fine hooked up like this, well other than it not reading sometimes, but I think that is from the beat up wire that ran down next to the headers.

I will try to trace the double pink wire to the fuse panel. I just wanted to better understand the wiring as I clean it up. I have a diagram for 79 but it shows that #30 is the fuel sender and it is hard to read that diagram.


My hazard lights also don't work, but my turn signals work fine. I checked the fuses before and I think I replaced the haz flasher. My turn signal switch has been replaced by my mechanic uncle. Does anyone know how this circuit works?

If anyone has experience with these issues or a good wiring diagram for haz lights or the gauge cluster and fuse box, I would greatly appreciate any help. I am pretty good with wiring, but it is hard to see where some of this goes. I don't want to tear the wiring looms apart to trace wires, if I can help it. I already had the bulkhead connector and fuse panel out, but I just put that back together. I am trying to get all my accessory feeds out in a box under the hood and I want to eliminate hidden places for wiring to go bad. My speed, temp, oil pressure, voltage, tach, etc. signals have new wires direct to the engine, so I only reused about a third of the wires from the original gauge connector.

Thanks guys

 

[CGT80]

It looks like the fuel sender wire must be circuit 30 but is pin 18 (corner) on my instrument cluster connector. I was able to verify that I found the right wire from my fuel switch in the dash and also the right wire to my gauges. I wasn't able to see where the second pink wire goes to. It looks like some wires may not be used. My schematic shows "omitted with gauges" and "omitted with v/8 gauges" for some of these connections.

I also found a black "relay" looking box under the dash tied into the fuse panel. It has 4 wires. Two are orange and one is green. It looks like it may be for the hazard lights but I'm not sure. It appears to only have two pins on the device. It is factory equipment.
Update: looks like it is the horn relay, according to my diagram.


I also have the haz flasher in the top left corner of the fuse box. It has two orange wires and a brown. I may have to dig into that stuff more after the truck is running and has power.

GM couldn't have picked a harder place to get to for a fuse panel. It's too bad I don't have another panel like it sitting on the bench. Hopefully this diagram will help me a bit more. It is just a slow process.

 

[CGT80]

I studied the wiring diagram for an hour or so and looked at what my truck has in it and now it is more clear. I was able to trace the haz lights in the diagram so now I will know where to check each part. It looks like the extra fuel sender wire may have been for a truck with different options than mine. I will leave the extra wire alone for now.

I wish I would have studied this diagram before. Many diagrams are vague but this one has everything. Hopefully I can get going on cleaning up this wiring mess tomorrow.