Ok i have had some major issues with my 78 f250 past couple of weeks. First my battery died from my tail lights being left on to long ( fixed that, just the sensor thing on the brake pedal) so i got a jump and it ran ok, i drove home parked it and charged the battery. then about 2 days later (just driving to and from work, about 10 min one way) it just died on me, and the battery was dead, so i charged it up again and after that it seemed to just have fixed itself. then my fuel tank selector switch got stuck between tanks and that had me stumped for a few days. then once i got that fixed it was fine, until the damn charging system decided to go on the fritz again. so i replaced the battery first as it had been run down several times and was not a very good battery to begin with. it now has 1000 cold cranking amps. so that is good, then i replaced the alternator, it was bad when tested so that is now fixed and good. then i still had [problems so i replaced the solenoid as when you would hook up jumper cables it would turn over with the key off and out, still no fix, so i then replaced the voltage regulator and that fixed it for about a day, then it just stopped working again. and if i am not mistaken when your charging system is running properly you should be able to disconnect your positive battery cable while the pick-up is running and it should still run. but when i do this to mine it dies instantly. that is how i knew the voltage regulator fixed it for a day, because it would run when you disconnected the cable. so now i am at a loss. does the voltage regulator on the instrument cluster have anything to do with the charging system working?

 

Disconnecting the battery and hooking it back up while engine is running can fry the alternator.
Voltage should be checked at battery with voltmeter while engine is running.

 

What should it be?

 

13.2 to 14.5 volts. The more the better, anything over 14.5 is considered, for the most part, too high.

If you get around 13.5 volts at idle with lights and heater on, consider it good.

Josh

 

ok well i checked and i don't get any different of a reading at the battery when the engine is running or when its off. i seem to get about 12 volts at the battery when the pick-up is running and when its off. i also get 12 volts at the battery post on the alternator when the pick-up is off.

 

Reading roughly battery voltage when the truck running means either Voltage regulator is shot or the Alternator is shot.

 

Voltage regulator is new as is alternator

 

Time to start chasing the fusible links.

Josh

 

Speaking from the experience I had with my truck most of the voltage regulators and alternators that are offered for these trucks at the parts stores today are nothing but pure junk. I abandoned all that stuff and did the 3G swap.

 

I feel your pain bud. Ive been dealing withnaggy electrical issues for months now. I replaced my battery and the alternator with a 64 amp chevy one wire alt. I just cant leave mine set for more than 2 or 3 days otherwise its toast again. Prettu sure its a small drain somewhere nut Im having a hell of a time finding it.

 

Haha and we both have 78 250s.

 

fixed the problem. was nothing more than some bad wiring on the VR and the ALT and a non-existent ground from the block to the frame and the ALT was not grounded. everything seems to working for now. Thanks guys

 

hey tik, disconnect your negative battery cable and use a test light hook one end to your neg cable and then touch the other end to your neg post on your bat. if it lights up then yes you have a short. start with your grounds, you should have one from the firewall to the block block to frame and if you have a hood light then one from hood to firewall, also not a bad idea to put one from passenger fender to frame (use 6 gauge for most of them except the one from firewall to block a 10 gauge works fine) also make sure your alternator is grounded good (10 gauge ground wire for it to), and then look at fuses. pull a fuse and then check it, then pull a fuse and check, and so on and so forth when it goes out that will tell you what component in your pick-up is causing the short then you have to trace it out through that component. had to do that twice on mine already. it works. let me know what you find.