My parking lamp circuit

WELL, what you know is that its a big short...36-40 amps on a parking lamp circuit is the edge of melting wires...so whatever is doing it is probably getting pretty hot, and the rest of the circuit is robbed of power. Unless you have access to a short tester unit (SHeffield Research or PowerProbe are the common ones for automotive) you will probably end up unplugging sections of the circuit and then retesting to see if you still are grounded. There were always issues with add-on trailer lamp wiring, so Id probably crawl under the bumper and see if there is anything resembling trailer wiring and disconnect ANYTHING I see (even if it appears undamaged) and see if that helps. Aside from that, you can attatch a small self resetting circuit breaker (say a 3 or 5 amp) in place of the fuse...it will pop almost immediately and should reset every few seconds...when its doing its on off dance, yoyu will have a pulsing 12v on the parking lamp system...wherever you stab power wires and see it, you are upstream of the short (Closer to the fuse, test farther away from the fuse in search of the short), wire tracing isnt easy without good equipment, but its not impossible with test lights and multimeters, just alot more time consuming.

Lets check the cheap and easy first. Does the truck have a harness to plug into a trailer if you tow a trailer? Did you buy the truck used? If you bought the truck used, the previous owner may have had installed a harness to tow a trailer for trailer lights. OK. First thing you need to do is steal the the "Welcome Mat" from the front door. Throw it on the ground right under the tailgate, climb under the truck and look under the truck. If I remember correctly, the the harness runs down the drivers side frame rail, branches off at the fuel tank, and continues down to the tail lights. Generally, the taillight harness is cut into and wires are spliced into for the trailer plug. If this has been done, You will usually see a bunch of wires taped up on the left side of the frame rail and a single wire run outside of the factory harness to the rt side to get a rt turn signal to the trailer. If this has been done, this is usuall easy to spot, and the first place to look for trouble. It usually looks like a ball of wires about the size of a curled up fist all wrapped up with electrical tape. Finding somthing like this is especially difficult by you self because by the time you put the fuse in, it blows before you get your head out from under the steering column to see what the light are doing. What I do is wire up a circuit breaker and plug it into the fuse block for that circuit, plug it in and turn the circuit on and see what happens. The circuit breaker trips, resets, and turns back on, trips, turns back on, etc. and I can look at whats going on with the lights, and I dont need a 5 gal bucket of fuses to figure out whats going on. Something else to think about, my wife had a 89 silverado, had an aftermarket alarm system installed, which is also tied into the the parking light system, the horn would honk,the parking lights flash, and the people that installed couldnt tell me how it worked. It devepoed a problem that would drain the battery while she was at work, and it wouldnt start when she tried to leave work, this happened 3 or 4 times and i finally traced to the alarm system. I finally had to uninstall the alarm system to get it where it was a dependable vechice for her to drive. Some things tolook at. Hoped this helps