Secondary electrical system

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Kody24

Junior Member
Joined
Jan 29, 2020
Posts
5
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2
Location
Oregon
First Name
Kody
Truck Year
1981 GMC
Truck Model
Camper Special
Engine Size
350
My first post here. I'm running an 81 gmc, 3/4 ton 2wd. Its had a few minor electrical issues since I got it just under a year ago. The only ones that bugged me are the mostly not there dash lights, and the headlights. Standard issues there. Dim, broken adjusters, and the high beams only worked for a while before flashing.
I run a lot of extra crap in my rigs. CB, lights, trailer brakes, amplifiers and so on and dont want to hack up my harness or run a ton of wires through the firewall to the battery so I threw together a complete secondary system that also runs the headlights, curing the flashing.
I started with the underhood fuse/relay panel out of 94 grand Cherokee. Because it was available, and the control wiring harness from an old gantry. Because they were handy and way more than adequate. Normally I'm as against throwing 110 rated AC crap in a rig as anyone, but these are identical to the wiring used for aftermarket dump setups so I'll accept it.
Just to clarify, this install is nearly invisible unless you're looking for the leads at the firewall and there is no giant rats nest of methtastic crap to short out. The fuse panel hides behind the glove box above the fresh air vent and all unused wiring is cropped short, capped, and tied up nice and tidy.
I started by running the 3 wire harness through the firewall in the same hole as the vacuum line for the heater controls. Then I opened up the relay panel and identified the wiring separating each group to its fuse or relay and marking which I was going to use. I then mounted a small junction block on the heater box and made jumpers on it, then soldered on a ring connector for my battery ground and attached it. Then I did the same for the two hots and hooked them to the fuse panel where the battery lead used to go, hooked the other end to the battery and verified power throughout the box and identified which wires do what on the relays. I chose a fused connection for the CB, then ran 6 wires to the drivers kick panel. The plug for the dimmer switch was shot and melted, so I cut it off, got a replacement, and hooked up the switched supply then hooked the high and low outs to my new wires and hooked the high and low beam wires up to the same harness. This leaves two wires for the brake controller later on. Back at the fuse/relay panel I soldered the two wires from the switch to the signal leads for two relays, and the return wires to the outputs of the relays. Tested them out, they work flawlessly and no flashing. There is more to do, but I'm going to be tearing the whole dash apart later to figure out why defrost isn't working and replace the dash pad so it can wait until then. I do plan on running all new heavy gauge wiring for the headlights later on, and converting them to h4 at the same time so the ****** job there is enough because I get high beams and removed the load that caused the plug to melt. I can take and post pictures if anyone is interested.
 

Turbo4whl

Supporting Member
Supporting Member
Joined
Oct 30, 2019
Posts
2,869
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6,443
Location
Downingtown, PA
First Name
Wayne
Truck Year
1974
Truck Model
Jimmy
Engine Size
350
Welcome from Pennsylvania. Yes we like pictures.
 

bucket

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Aug 3, 2010
Posts
29,087
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Location
Usually not in Ohio
First Name
Andy
Truck Year
'77, '78, '79, '84, '88
Truck Model
K5 thru K30
Engine Size
350-454
I took a much simpler approach, although my stock wiring was functioning fine. My goal was just to run several accessories and not rely on the factory fuse box. I ran a dedicated power and ground to an 8-circuit fuse panel that I mounted to the firewall, under the dash. Next will be an additional 6-circuit panel that will only have ignition power. My radio, cd changer, tach and wiper delay box will then get their ignition feed from that.
 

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