i have a 1998 ford f150 truck, it will not charge the battery alt. is rebuilt had it checked twice battery is good 12.50 oms. Any ideas?

 

Nice to have you here!

If the alternator checks out OK and the battery is strong are you sure you don't have a short somewhere? When the truck is running, have you checked the alt to make sure it's charging the battery? Voltage regulator?

 

Alternator while running should be higher than 12 volts with most vehicles. 13, or more, would be more like it. Check for the output of the alternator while running (even a bit off idle) and see if you need another rebuilt Alt.

 

When the ignition is off, 12 volts at the battery is normal. When the ignition is on but the engine is not running, battery voltage should be 11 - 12 volts. With the engine running, voltage at the battery should be 13.5 - 15.0 volts.

 

No idea where you get "oms"?

KRM02 has got the right idea. My '98 has sat for weeks & the pretty fresh battery still read 12.16 volts. When the key is switched on that dropped to 11.80 volts. Quite obviously charging, after sitting so long & on high idle, it read 14.36 volts.

IMO if you "have a short somewhere" you usually find out about it pretty quickly, especially in the large wires between alternator & battery. Shorts will ultimately pop a fuse/fusible link or smoke the wire until it burns out. More likely is a bad terminal or connection, that produces high resistance. This can fool a voltage regulator, acting like a fully charged battery.

 

As club wagon mentioned it might be a blown fuse.

That was the prob on my Explorer when it was'nt charging. Replaced the fuse & problem solved.

Strangely enough the fuse is listed as "Generator/voltage regulator" on my 97 Explorer. Go figure. Tradition I guess.

 

Nope, Ford classifies the device as a Generator these days.