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I have an ’87 W100 that I bought to work on and drive for fun. A couples months ago the battery died in it, and i didn’t think nothing of it because it was a 3 year old battery. So i replaced the battery and it started and ran fine i didn’t hear any unusual noise coming from alternator and everything electronically worked fine. until the next day when the new battery died on me. So I figured the alternator burned from trying to charge the last dead battery. So I replaced the alternator and charged the battery and took for a spin it ran fine again and with no noises. So the next day went to go start it and the battery was dead again. headlights are not working well especially the high beams i do have a winch mounted on the truck but it cant draw any power also the ignition lock cylinder needs to be replace and probably the ignition switch as well. also the radio doesn’t stay on while driving it flashes on and off constantly probably because of the ignition. i do not believe there’s a short in the wiring anywhere because i did the old negative post to negative trick with the test light. but if i fully charge the battery to 12.6v exactly and then start the engine the voltage drops to about 12v instead of jumping up to 14v or 15v. and with the headlights on it drops even more and even more when shut off and started again. I’m completely stumped and yes there is plenty of tension on the alternator belt.
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Are you sure it’s a W100 and not a W150? It is a Dodge pickup, correct. There are several types of systems on those trucks depending on engine size.
If it has a Chrysler system it has an external voltage regulator that I believe is mounted on the firewall. Once we get all the information about your truck it will be much easier to diagnose.
Yeah… My memory isn’t that good but it’s usually a silver box about 5 by 4 in. bout 3/4 in thick with a single plug with a phillips screw in the center with 2 wires on it. 2 bolts hold it down. It might also be bolted to the inner fender somewhere.
Also note that a broken wire from the alternator to the regulator could cause this issue as well. Never discount that possibility. Thankfully a regulator is like $20 and easy to replace, so its a good way to test.
If that STILL doesnt work, its time to pull out a multimeter and start doing continuity checks between the alternator and regulator. Reason I say continuity and not voltage is because I dont have a wiring diagram with voltage specs and dont know them either.
okay, so I replaced the external voltage regulator and it did nothing. so I had the alternator tested and it was fine. then I thought I fired the cells in the battery so I warrantied it and got a new one but im still having the same problems. I did another voltage test with the new battery and when I started the truck the voltage admittedly dropped from 12.8v to 12.3v. Instead of jumping to jumping to around 14v. while the truck was running I turned on the high beams and the volts dropped again (as expected) to 12v. But when I turn off the high beams the voltage jumped back up to 12.3v. Does this mean I am getting a charge just not enough charge. I looked up the part number on the alternator and it is the correct one for this truck. Also while I was checking my turn signals it appears that I have to have the key turned to a very specific location in order for them to work. I know the lock cylinder is bad and probably the ignition switch too but could this be my problem? I also have a thought that maybe the starter is draining the battery too quickly?? Please let me know what you all think!! thanks agian
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