I've got an '86 F150 v5.0 that has been problem free until recently. I had her die one night on the way home - i figured battery or alternator problems. Checked out the alternator and replaced it. No problems for a few days on short drives. Then after driving for 90m or about 60m, the same thing happened. LIghts got dim, and fuel gauge slowly went down (all other gauges were fine), and then the engine simply quit. Wouldn't turn over, but enough juice to run accessories for a bit. A jump got it started, but it would only run for a few minutes under full load. The battery would take a full charge, so appeared to be fine. But just to be certain i swapped it out. 90miles later, the same thing happened. All I can figure is a bad wire between the alternator and battery? Thoughts?

 

First of all.. You only have to post one time.. We will find it... Second, Is the battery light coming on when you first turn on the key without starting the engine? If not there is your problem. Let us know and we will go from there.

 

Yes. The battery light comes on when I turn the key but don't start the engine. And the battery gauge reads dead center. thanks!

 

If you can get the truck started check the amps coming out of the alternator, sounds as if it's not putting out. Next I would check each individual cell in the battery,could be the alt. is putting out but battery is not holding the charge leading to a dead cell. With a dead cell the battery will take a charge but won't hold it. But most likely I would lean towards the Alt. maybe putting out a small amount of amperage. Maybe NGM will jump back in with other suggestions.

 

You pretty much hit it on the head. MAke sure all the connections are clean and the cables don't have a voltage drop across them.

 

So -- I've tested the alternator to be certain it's putting out properly -- all looks good. I tested the battery our in my other truck and found it charged, held a charge, and worked with no issue. All connections are firm and tight. Is it worth replacing some of the wire leads to/from the battery or alternator?

 

Before you start replacing wire ends. Do you know how to check resistance on the wires with a meter? If not find some one that does and check for a broken wire which generaly can only be found by checking resistance. Next have you added any aftermarket acc. or new stereo, something that might be a constant drain on the battery? Your turn NGM.

 

That sounds good to me. Again do a voltage drop test also.

 

replace your voltage regulator... if you have the external type. i had the same problem and thats what it was.