I have a 72 F-100 and am having a perplexing problem with my electrical system. My problem is that I cannot power to anything except the horn. I posted a thread about this a while ago and I was advised to check the starter solenoid and the fusible link near the starter solenoid. I did all of this and everything was fine. The battery is new so no problem there. I checked what wiring I could see and everything seemed fine. Anybody else have any ideas on what could be bad? Again, nothing (ignition, lights, wipers, etc.) works except for the horn.

Thanks.

 

You said the fusible links were "OK" but did you do a physical inspection only? You must check that electricity is getting through the wire.
The best way to do this is to get a test light with a point on the end of it. Ground the loose end of the wire, and with the point probe into the wire. For fusible links, you must do this downstream from the electrical source, past the fusible link location. Push through the insulation to the wiring to establish a contact. If the light glows, you have juice. (Be careful here! Don't push all the way through to the metal on the other side of the wire, because you will create a direct short if you do, which may burn up wiring! I suggest a small piece of thin plywood or plastic used as a backing behind the wires you are probing, so you can safely push all the way through. Don't use your thumb or finger either on the back side of the wire. The points on those probes can send you to the hospital with a deep infection.)
Fusible links usually crisp or bubble the insulation around them when they fry - but not always. Check these first since they are the most likely culprit.
You may find it necessary to check each and every wire going into the firewall, and going into the fusebox.
Time consuming yes, but that is the only way you can ensure you can find wiring issues.
Pull the fuse box and check the backside for burning or corrosion.
If you have a junction box on the firewall, disconnect it and check all the contacts for corrosion. I do not remember if the '72 models have junction boxes, or if the wires are grommeted in the firewall.
In any case, check all junctions under the dash in the truck. You may find one with corrosion which may be the cause of the entire problem.

Hope this helps.

 

I'm with Banjo. It must be the link or the fusebox. My money is on the fusebox. Did you inadvertently blow your fuses somehow? Let us know and good luck.
jor

 

I did test the fusible link for continuity and everything was ok. I checked the fuses but not the backside so I'll try that. Yes, I did have a minor accident. I absent-mindedly hooked up my jumper cables backward. I don't know if that is what caused my problem, but I'm guessing it is.

Thanks.

 

Do you have any power to fuse panel?? None??

I would trace the fuse link. I was thinking it went thru the alternator and then into cab. It's been awhile since I looked at mine so I may be out in la-la land on this one.

I would bet you burnt the wire somewhere along the line. Trace it and you'll probably find the problem.

 

There is no power to the fuse panel.

Does the fusible link travel all the way from the starter solenoid to the the fuse panel? Where does it end up? Just thought I would ask before I started unwrapping the wiring harness and taking things apart.

Thanks.

 

I expect you have a problem with the fuse box - the horn relay gets its power from there, as do most other things. On mine, it was burned on the backside and some things worked, others did not.

I fought it for a few years, and then replaced it with an aftermarket fuse block.

 

I checked the back of the fuse box and it is not burned. Could it be anything else besides burnt?

 

You said that you checked the fusible link for continuity, then you asked if it continues to the fuse panel. I don't think you know exactly where it is. The fuse link is connected between the starter relay and the alternator. It is only about a foot long and is wraped in black tape. Check for continuity on the BAT connection of the alternator. No voltage probably means the link is burned. Heavy reverse current will burn the fuse link.

 

I'll admit I was misinformed and I thank you for your correction. I was under the impression that the link had a fuse inside of it. I know where the one end of the link is (starter solenoid) but was unsure of where it ended up. So would I now be right in saying that the entire thing is the fuse and I should probably check it again? Thanks again.

 

The fusible link is actually a wire several guages smaller than the wiring it protects. It is designed to burn out before the alternator or other wiring is damaged. Yes-I would start checking there and good luck!

 

I would like to point out your igntion switch box feeds the majority of the circuits in the truck and has a direct link to the battery. It is possible you nuked the switch or a wire has pulled out or burnt out. Remove the box from the dash with the harness attached. The two main wires (one yellow one red?) with their color and size will tell you they are the main feeds being about 10 guage. You should have 12V constant on at least one of those two wires. I think it is red with a black stripe on the left side of the box. I do not have a diagram in front of me to verify it.