Hey everyone I have a 78 f100 and have recently been haing some issues with the alternator,voltage regulator,battery,wiring (basically everything on that passenger fiewall that has a wire to it except the ac)

My battery at first started dying and lights flickering and all until it finally just shut off in the middle of the road. CHarged it up replaced the alternator got better the next day but happened again. Charged it up again took it to auto zone to get it tested everything seemed like maybe it was the voltage regulator so we replaced it and it worked better and longer than it had the other times but then died again after a good hour and thirty of running around town.

At this point it seems like either my battery just wont hold a charge or my wiring is garbage, which the later wouldnt be too surprising. I cleaned the wires up and made sure they were tight and good but its dies on me. The guy who had it before me doesnt have the original set up of wires that go to the back of the alternator and their is one wire with a cap on it that im not sure where it goes.

This is the only thing that sticks out to me as to why this might be happening and I was wondering if i could get some info on similar issues or any kind of help.

Thanks again, Michael.

 

Does your truck have an ALT light or an ammeter gauge in the dash?

 

man, i just had the same problem with my truck, same year, same model. This is how I fixed it.

Replaced fusible link wire from alternator to switch. Since there are 2 fusible link wires on the battery side of the switch, I put the ignition fusible link on the inside closest to the switch, and put the alternator fusible link on the outside so it made direct contact with the battery cable.

I also removed my voltage regulator, sanded the paint off the firewall, drilled new holes and bolted it back up to make sure it had a good ground.

Worked for me!

Good luck though, wiring issues are a pain in the butt!

(Also, make sure your battery has enough cold cranking amps. Mine has 690, and its barely good enough.)

 

No, it doesn't have a ammeter although I may add one soon enough. Not sure what an alt light is but im pretty sure it doesn't.

I'm definetly going to try everything you did.
The guy who rebuilt the engine did a good job with that but as far as wires go he was a fool lol over half the wires are spliced and covered with tape dangling right next to the engine some dont even go anywhere. The other day I pulled one out that no kidding was cut on both ends but was stuck under the dent and hood and between the passenger door hinge area.

 

Thanks! by the way

 

The ammeter is a gauge opposite the fuel gauge that has "D .... C" across the face. The ALT light is simply a red light on the instrument panel that says "ALT" in white letters. You'll have one or the other. The reason I ask is because the wiring is significantly different between the two; once you identify your setup we can go from there.

 

Ah ok yeah I have the ammeter then, sorry im still learning all this.

 

Wiring problems are a pain in the butt. Fortunately, these trucks are pretty simple. There are only 3 parts in the charging system. Alternator, Voltage Regulator, and Battery. The alternator and battery can be tested. Just because they test good once, does not mean that they are always good. You could have an intermittent failure in the alternator. The wiring could be bad.

You need to go through and check both your ground cable and the battery and make sure they are clean and secured. Also check to make sure the plug on your voltage regulator is snug. Then check the wires from the regulator to the alternator to make sure that they are all in good shape. Make sure the plugs on the alternator are completely plugged in.

Wiring is a pain, but this one shouldn't be too hard to figure out!