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Little Trucks, Big World

OK I have a had a slow battery drain problem for a long time, another issue caused me to tackle it and I think they are both related but lets stick to one right now. The wire is the heavier guage white on the lowest fusable link terminal, the fusable link is fine. The wire shows 4+ ohms on the ohmeter (see pic). I removed every fuse one at a time (Twice) and there was no drop in resistance. Standard op for battery drain. Out of frustration I turn the headlight switch to on and the meter read 000. Now this is with the battery disconected so the relays were not operating and that is a very large wire for just a light switch.  FSM is not much help.

Question 2 and make sure you read the whole above statement because this is seperate but related. I had a voltage drop of 2volts to the rear tailight harness. After cleaning all plugs and terminals I am down to a 1 volt drop between battery and rear tailights. This is and additional clue, but lets see if we can solve this without wild ass guesses.

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wow,that picture is scary...

When you pull all the fuses and still have parasitic drain I would suspect a shorter diode in the alternator. Dead giveaway is AC voltage present at the battery with the engine running. If a diode shorts, it allows current flow back to ground. Had it happen once before. Hope it helps.

I'm assuming you have checked that your brake lights aren't staying on due to a faulty brake pedal switch...

OK, for question 2 a voltage drop of 1 volt at the rear tail lights isn't a real big issue in my opinion because lets say conservatively you have .5 amp draw from the tail lights, it only requires a 2 ohm resistance in the wiring to get a 1 volt drop.  2 ohms through 20 something ft of 30 year old wiring and connectors isn't out of the realm of possibility...

Now the question is was this 1 volt drop with the tail lights lit, with the brake and tail lights lit, or just measuring an open connector with no lights lit?

I agree with Patrick that parasitic drain can often originate at the alternator, both from shorted rectifier diodes and also from a faulty regulator.  Disconnect the wires to your alternator and check again.  I believe the large white wire you are speaking of is the sense wire for the alternator regulator.

And a better way of testing than pulling one fuse at a time, is to pull all the fuses, then check it. Then start inserting one fuse at at time.  Because in trucks this old there is bound to be a lot of user re-wiring and sometimes circuits get crossed in the process.  If a circuit is crossed with another, and one of the two has a short,  if you pull just one fuse at a time the problem won't go away...

A little confused on your picture there, I can't see for sure what range you are on on your DMM, but the ranges below it says 200, then 2000 so I have to assume you are in the 20 Kohm range and if so, the meter isn't reading 4.75 ohms, its reading 4.75 Kohms (4750 ohms)...

Thanks for the replies. I think it is in the light circuit. The voltage drop was noticed when I hooked up trailer and the lights were very dim. Taillights are brighter now and I swear the runs better.

We have a WIN! Thank you Patrick and Corey! I was barking up the wrong tree, the three white wires had me confused. You will see the alternator has some kind of internal ground going on when connected to the batt. terminal.

Well my pictures would not upload. I did continue the terrminal cleaning and everything is smoother. It was raining so I kept going rewiring and soldering the old stereo system that has not worked right in years. My 78 year old nieghbor came over and said with all his windows and doors closed (rare in Florida) his wineglasses started rattling in their rack. He couldn't figure out what was going on until he opened his door and heard the music. I had a battery charger running because the system uses so serious juice, he said all he heard was bass in his house. Mission acomplished and I made a road trip to the grocery store blasting my Miami Vice soundtrack there and ASIA on the way home. If you want to improve your old trucks function all around take the time to clean all your accessible terminals, it is time consuming but free.

Lol, good job, great story...

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