So I parked my '73 F-100 in the driveway last night. It had been running fine. Got up this moring to go to work and went to start her up. Nothing!!! Totally dead electrical system! Nothing but nothing worked, no tell tail clicks from relays...nothing. So I checked the battery...fully charged!! Checked the battery terminals and connections at the starter relay...all in good, tight, clean shape! I tried the horn, headlights, and brake lights (which on my truck are independent of the ignition switch). Nope! Dead.

I swapped out the ingition switch. No change. I considered the fusable links, but that wouldn't kill the lights or horn (or would it). I can't find any obvious shorts (but the damn battery is fully charged-yes, I tried it on another car). I've fixed a lot of stuff on trucks, but I am throughly and completely STUMPED on this one!! Any ideas? Thanks, Polkat

 

Headlight circuits are often protected by a fuse link.

'fenders

 

Hows the battery ground? You may want to check it as well. I would say from your symptoms that it sounds like your battery. Try a jump just to be sure..

Bil/

 

Battery is fine, and I've tried other known good ones too. Since my first post, I've traced a few things. It seems that from the battery side of the starter relay, there are several other wires going off into the truck. One is a heavy black wire with yellow stripes. It appears that this wire carries the main current load for all systems in the truck not associated with the starter (however it also carries current to the starter switch which in turn works the starter relay).

It seems to me that if there were a break or bad connector somewhere along this wire between the relay and the...I guess the first thing it hits (fuse box?), it would cause all the symptoms I've described. I'll try tracing that unless someone suggests something further. Thanks for the help.

 

Recheck the ground connections. See if you have a connection from the block to the firewall. Let us know what you find.

 

Instead of tracing the wire why not do voltage checks with a meter or even a trouble light? Check for 12 volts at the starter relay post, then at the fuse box.
Could be a bad power wire but there are at least 3 that feed into the truck ,if my rememberer is working correctly , most circuits are powered from the big yellow wire but there are other circuits that use the other power wires. And since nothing on the truck works..... it could be a bad main ground wire.
Try hooking a jumper cable to the negative battery post, remove the battery negative so you get good contact, then hook the other end of the jumper cable to a good clean metal spot on the engine block.
If it works then bad ground....if it doesnt try the same setup with the positive cable but go to the starter relay post instead of the block
If that works it is a bad positive wire.
Hope this helps, got to go back to work before the boss sees me at the computer

Sparky

 

Thanks Sparky, and everyone else. Problem fixed. Now, I've seen a lot of weird stuff working on cars over the years, but this one rankls right up there with "Stranger then fiction" car repairs.

It was the ground. I followed the ground lead from the battery to the engine block. Well, in this case it was attached to one of the bolts that holds the alternator bracket in place. I made this ground myself just after I got the truck. The cable was originally attached to the adjustment bracket for the alternator as someone's afterthought, and while it worked, it held the cable about 1/4" from the fan!! Well, I knew where that was going so I pulled it.

I pulled another bolt from the bracket (one that goes into the end of a head) and used a file to clean it up brightly, and wire brushed the inside of the bolt head, and used a new washer. I didn't bother to check it out yesterday because it was still tight and bright! Well, today I pulled it loose thinking that maybe there was some corrosion inside. Nope!! Clean as a pin and nice shiny metal. Also, the ground cable itself is in excellent shape! Now, by all the gods of metallurgy and electronics this should be a good ground!!! There is no scientific reason why it shouldn't!

Still, on a whim, I chose another bolt on the bracket that also goes into a head, cleaned it all up as before, and attached the ground there. Now, it works great!!! This is a solid, one piece aluminum bracket that I have attached both these grounds to, with clean bolts and new washers. I tried to read continuity between the two different areas of the bracket, and it read fine. Put bluntly, there should be no difference between the two mounting points!!

So it's weird to me. Only one thing comes to mind. The bracket is aluminum, the connector on the end of the cable is steel. Is it possible that after a given length of time, the metals react and some form of resistance is created?? I guess I'll know if it happens again. Unfortunately, there is no unused bolt hole on the end of the heads themselves, which would certainly be the ideal connection spot. But if it happens again, I guess I'll have to rig something.

Anyway, put that in your file of weird fixes!! Polkat

 

Ah ha Steel and aluminum dont like each other, they are dissimiliar metals which encourage corrosion like you wouldnt beleive.
Best to ground it to the block, thsoe aluminum heads/intakes/etc arent the best place to ground things. Although alumium is a better conductor than copper or steel it corrodes way too fast when exposed to air or other metals.

Sparky