I have an 83 F150 5.0 liter. I just replaced the alternator and battery (perhaps hastily because they have not solved my problem). Anyway, the problem is that the truck will not start with the current battery. It tries to crank over but its like there is not enough power coming from the battery. If I get a jump the truck will start immediately without any hesitation. Once started it will run indefinately without any dimming of the lights or power hesiation or anything. If I disconnect the battery the truck dies which implies the alternator is not functioning properly. However, when the truck is running I am getting 14v at the battery. The battery however does not seem to retain that charge because at rest it only shows a reading of 11.6v, so perhaps its the battery as well but they were both new only a month ago. Any suggestions would be greatly appreciated.
Thanks

 

This will not tell you anything, as an alternator needs DC exciter voltage to charge. All trucks will die sooner or later with the battery disconnected.
This is also a very bad thing to do as it can make more problems for you.

Make sure all connections are clean, from both sides of the battery, as this could be a bad ground going to the block, bad cables or contacts in the solenoid.

 

Hi, Thanks for your reply but I have already put new battery cables in because that was a suggestion I was given from a friend. Another suggestion I received was regarding a parasitic drain which I still have to try and figure out how to test for. There shouldn't be a drain though because I have nothing hooked up to this truck unless the starter is somehow always engaged. Any other ideas would be greatly appreciated.

 

The problem is between the battery & the starter, somewhere along the heavy wires that connect them. I'd remove, clean, & tighten every connection along that line - that usually fixes this problem. Just do ONE connection at a time. Many people pull everything off the starter relay, and then get them wired back wrong. Everything but the wire to the starter goes on the front post. Don't forget the frame ground (just inboard of the R spring tower) and the block ground (at one of the starter bolts).

Another likely suspect is the starter relay. They're known to burn their contacts internally, especially if you're using the old-style relay. It's better to use the '92-96 style since it's MUCH less prone to that type of failure, and doesn't cost any more. It doesn't matter if it's diode-supressed, so get whichever one is cheaper, but buy a good brand from a good parts store. Stay OUT of the zone.