My voltage started out with 14 and then dropped to around 10. My truck will not start and my lights are dim.This is the 3rd time this happened in a year. The first two times I replaced the alternator. Was replaced about 2 months ago. What else could be the problem?

 

Have you disconnected and checked the battery? It could have a shorted cell, and if so it'll pull heavy current on a battery charger, but never get above 11v.

 

What year is your truck? If it has an external voltage regulator that could be your problem.

 

The battery is brand new and checks good.

 

The truck is a 1987. Does it have an external voltage reqgulator?

 

I don't know about the '87s. I had an '85 with an external regulator. It was mounted on the passenger side fender well.

 

Clean all grounds. And there is a bunch

 

Maybe its me, but I've had terrible luck with Ford battery cable ends. Check to make sure you're getting good contact there.

 

I had the same problem with my 88. What I did was do away with that 6' long ground cable that is no bigger than a cheap set of K Mart jumper cables. It goes from the negative post on the battery all the way to one of the starter mounting bolts. When I would start it, the radio would loose its memory because the voltage dropped so low. I got a #2 cable around 18" long and ran it from the negative post on the battery to the alternator bracket, there is a bolt hole on it. Don't forget that small ground wire on the battery end of the old cable, it is for your fuel pump system ground. I done this two years ago and have not had a problem since. It charges better and cranks like it should now.

 

I just started it and it seemed to start up fine. The guage is still reading around 11 volts and not going up

 

What year truck are we talking about? On early computer models you can remove the neg cable on batt and see what gauge dose. It should center as if the batt was fully charged if you have no hi amp drains like stereo or head lights on. If it dose, turn on head lamps and it should charge harder. If it dose your batt is shot. If it discharges your alt is weak. Be sure to be on fast idle as most factory alts won't put out enough amps at low idle to run ign. and it will die. If it dies at fast idle when neg cable is removed than alt is shot. Remember to have #2 ground cable to alt as stated earlier. Most hard to find weak voltage problems are weak or bad grounds. I see most people do engine swaps or R&R and not put grounds back on block to frame and block to cab. You can't over ground your rig. the more lights and power you run the heaver the ground sys must be as it carries the same load as the pos side.

 

As an after thought is this the stock Ford amp gauge or aftermarket? Do not trust the factory gauge.

 

It is the factory gauge. It was pretty accurate before. I can tell when the voltage is low because the light are dim. I know if I change the alternator everything will be good for a while. This would be the 3rd alternator. Something else has to be wrong. I am going to clean all of the grounds. This happens all of a sudden.

 

Mine reads around 14+ volts.

 

Thats what mine was reading until this morning. I have it running now and it is about 12 volts. Will try to make it home and then I will play with it.