hey all,
I have a 1992 F-250 (diesel, 4x4, ext. cab, auto trans) and for some reason my battries seem to be draining. i will jump the truck and it will run fine. shut it off and it will start ok. but if i let it sit for 4-6 hrs and try to start the truck, it just "clicks" or turns over real slow, like when you have a dead battery. by the next mornong, everything is completely dead, no lights, no starting, nada. i took the battries to autozone to be tested and charged and they said that they were fine. what should i do now? thanks for all your help.

~pete

 

Check for a shorted out alternator, if the diodes are shorted out they will drain the battery back to ground in short order. Is the alternator warm to touch even if it hasn't been running? With batteries freshly charged, you could disonnect the alternator power lead before re-connecting the batteries to see if it still drains them down over night. If so, something else may be shorted to ground and will take a meter and isolating circuts one at a time to find the problem. If you leave the batteries disconnected overnight do they still have a full charge in the morning- or do they go dead overnight- indicating a internal short in the battery-(in spite of what they autozone people say). Hope this helps.

 

If you remove both negative battery wires..... just using the pax side (USA) place a test light between the neg wire and the battery neg post..... if there is a circuit still on the light will illuminate. Now start pulling the fuses one by one.....and replace them.. if the test light goes out...... you have now found the circuit that is draining your batteries.... You can check brake lights, glove box light and under hood lights also.....in the dark.

 

Try this test. Pick the battery with the smaller wires going to it. If you have smaller wires going to both batteries, you may have to try this on both.

If the light does glow bright, then it is confirmed you do have a drain. You can start pulling fuses to see if the light goes out, and you can also take the wires off the alternator to see if it is causing the drain.