Voltage regulator, battery drain
 

1987 F250 Diesel, I have a battery drain. I disconnected negative terminal and used test light while pulling fuses one by one (doors closed no dome light), the light stayed on(bright). I unhooked the alternator and the light stayed on. I unhooked the voltage regulator and the light went off. Does anybody think I have found my problem or is there something else I should be doing?


Thanks

If the light went off it sounds like a draw. Get a new or different one and test again.

Did you have the test light between the negative battery terminal and the end of the negative cable?

Jason

Yes I had the test light between the neg. cable and terminal. But the light goes off if I disconnect the alternator or if I disconnect the regulator so I guess my question is "how do I know which is causing the drain?"

If you disconnect either (alternator or regulator) it goes off? Maybe you have a draw at the wires from the starter relay (solenoid?) on the fender that goes to the alternator/regulator.

There's your problem. You need to use an ammeter (not a voltmeter) in place of the test light. Then you would pull the fuses one by one, checking the ammeter each time. You should have no more than about 50-100 milliamps of draw with everything off, preferably closer to 50 mA or less. When you pull a fuse and get a significant drop in amperage draw, that circuit is your problem.

One other thing you should check is the voltage between each cell of your battery. Pop off the vent caps and stick the probes into the water of each adjacent pair of cells (i.e., 1-2, 2-3, 3-4, etc.). You should get a reading of about 2.1V between each pair. If you have a pair that reads 0, you have an internal short and the battery is bad.

Jason

You can also use a test light, works the same was, when its dim the draw is low, when its bright the draw is high. Well on ur alt isnt the reg but into the alternator? Just get a new alt and plud it in, no need to swap it it. If ur light is still bright then there is another prob, is the light goes dim with the new alt plugged in then you know ur alt is messed up.

Battery drain
 

I have a 1988 Ford F-250 7.3 diesel and have a battery drain problem let's say today it turns on and drive it all day long and get home and park it and the following day the batteries are dead
I took it to get a check on the battery's and the altenerator and both are good the altenerator puts out the 12 volts
I'm not sure if the if the battery's should be a problem because they both are around 700 cranking amps
By the way the problem gets worse when it's cold

You really should start a new thread for your problem.
This one is seven years old...

12V is not enough. You should see something over 14V with the engine running.

Have you tried using a test light or ammeter to trace the draw?

Do you have a separate regulator mounted on the fender?
Does the back of the alternator feel warm after the truck has been parked for an hour or two?