I am chasing three issues related to dash wiring on a '71 GS 455. One is related to not having any power at the 4 amp fuse on the fuse block and therefore there are no insturment lights, not power to the radio, no power to the lighter and maybe something else. The other issue is that as soon as I connect the ground wire from the harness into the harshell connector for the headlight switch and move the knob to the first position, maker lights, the 20 amp fuse blows out instantly. The third is that the buzzer and horn relay have constant power but no ground. So the buzzer is on all the time when the door is open with or withour the key in the ignition cylinder and the horn does not activate via the horn button. Any help would be appreciated. I have a complete 1971 Buick Service Manual, the Fisher Body Manual, and factory assembly manual.
Sounds like you have some serious shorts. May be easier to replace all harnesses or at least take them all out and examine them inch by inch. Not fun. Maybe you bent something when installing the engine harness to the fuse block?
Possibly just one problem....maybe not. I do not believe you should have any power to the 4 amp fuse unless headlight switch is plugged in. The lights have to be on in order to show power to that fuse. The BIG problem is your headlight harness blowing the marker fuse. I would unplug the connectors at the firewall and try to feed power to the brown tail light wire in the trunk. Plug in the headlight switch and see if it blows any fuses. If it does you have isolated your problem to the dash area. If it does not you have a problem under your hood with your headlight harness. Good luck ,it is probably a shorted wire, you just have to find it.
This is going to take a methodical check of each circuit to find the problem. A couple of things here concern me, and they would be the first things you look at: If the 4 Amp fuse for instrument lights has no power, it has no effect on the lighter (20 or 30 Amp, I forget which, but it's like a toaster, lotsa Watts) or the radio, which is 10 or 20 Amps. You are going to have to study the wiring diagram carefully and trace the wires. This is probably the most difficult part of any vehicle troubleshooting there is. Just take your time, get some info, and ask more questions. This board is the best at answering questions, but be sure you try to ask the right questions (that's a tough one, believe me) and filter the answers (like any other resource). This problem could cost you hundreds, if not thousands, if you take it to a shop.
Also if you go the new or used harness route beware that the gauge cars used a different harness in 71 with integral tach wire and gauge connectors. There is also a hood tach wire taped back to the main harness when not equipped with a hood tach.
So here is the update. I think WE, I recruited a friend to help, have gotten to the root of the dead short in the dash harness. The headlight switch that was in the car has had the ground terminal ground off of it and the ground was not connected to anything. that is the reason none of the lights or radio worked when I started working on the car. By replacing the headlight switch with a switch that has a ground terminal on it and attaching the ground to it; IT ALL WORKS, for now and long into the future. I must say that the factory wiring diagram leaves a few things to be desired. Primarily how small it is and difficult to read for those of us without 20/10 vision. Then there seem to be a few important details left out of the wiring section. Anyway, by looking at the big car wiring harness diagram and ASSUMING that the engineers would apply the same processes and procedures to both vehicles I determined that the ground for the dash wiring should be on the terminal outside the hard shell instead or inside it. Next up is installing the radio and see if it works after replacing the speaker and the diode that are both required to be working in concert for the radio to function. Then onto more re-assembly of the dash before it goes to the interior shop next week.
