Ok I am creating an ASIS wiring diagram, before I rip out old stuff. Need help identifying these components. pic 1 a small can on firewall below steering column device with two wires that go into main bundle and through firewall pic 2 round can 3 wire to bundle , on firewall driver side pic 3 black fuse can for tail and stop lights pic 4 white block one side to pos of coil, the other to starter pic 5 sliver can left terminal to horn, center to right term of black fuse box for brake lights, right term through small grommet in firewall. In a previous post, I was confused by having a fuse panel like ez wire bundle has. Am I correct that originally there was no panel, more inline fuses of ones like pic 3? Thanks Denis
This info based on 1951 GMC wiring diagram, your mileage may vary, but not much. Pic 1 is the brake light switch. One wire comes from the fuse box (pic 3). The other goes to the brake light bulb(s) in the back of the truck or to the turn signal switch if you have one. Pic 2 is the headlight dimmer switch. One wire comes from the light switch in the dash. The other two wires (high and low beam) go to the terminal board on the inner fender panel near the left front corner of the hood. Pic 3 is the fuse box. One for brake lights and the other for tail lights. These are the ONLY fuses in a stock electrical system. Pic 4 is a ballast resistor. NOT stock. It is used on 12v systems to reduce the amount of current/voltage available to the coil and points. Normally, one side goes to the the ignition switch "run" or "ign" terminal and the other side goes to coil+. Pic 5 is a horn relay. Also not stock, but a lot safer and more reliable than the way the horn was originally wired. The wire going into the cab will make its way to the horn button. The center terminal is 12v into the relay.
Sounds like they are all useful parts and that I should rewire them as is? I am going to add directionals. Denis
Your new harness should have leads that go to these items. I don't remember if any of these need to be replace if you are going from 6 to 12 volt.
I'm guessing it is already 12v, based on having a ballast resistor. All the components in the pictures will work fine on 12 volts.
New question / observation. The "terminal boards" on the fenders. Are they a shared power board or are the three contacts independent? Mine are shot, Where can I get new ones? I am amazed I didn't have a fire, the wires are chaffed, raw and bad!
Some have 3 terminals Headlamp Terminal Block-3 Terminal-Classic Chevy Truck Parts and some have 4 terminals Headlamp Terminal Block-4 Terminal-Classic Chevy Truck Parts. Terminals are high beam, low beam, "parking" lights and I don't know what for the 4th one. If it were turn signals, you'd need 5, not 4.
