Need help...electrical issue on an '02 7.3 F350. So the ol' diesel's dash shows a “battery” light...I was just driving along minding my own business. Get home, check voltage on both batteries while disconnected. Voltage is similar and reads good. Connect batteries, start up, both batteries charging within hundredths of a volt from each other. Waited a week to do anything about it. It's cold out, gonna get colder. Fire it up and let it idle 15-20+ minutes. Battery light and, now, ABS light are on. They don't go out. (I've seen the ABS light in the past, gotta reboot it with a short drive). Couple days later, grab an OBD scanner from my buddy, just cuz...no codes. Vehicle struggles to start and fails. Do a load test and crap, both batteries are done...surface charge only. I thought the batteries were from 5-6 years ago which woulda been a good life but, it turns out, they're stamped 01/17...NAPA Legends, kinda bottom shelf. Get new batteries, install, take a short drive. ABS light goes out as I was sure it would. Battery light stays on. Now, the important shit... I'm guessing a faulty alternator? Would a bad alternator give a code? Could it have killed the Legends if it was bad? It showed a charging status as indicated above...could it have just been a weak state of charge on “ghost” batteries? Not an auto guy so I'm not sure how to isolate the alternator to check its output.
Now, the important shit... I'm guessing a faulty alternator? Would a bad alternator give a code? No Could it have killed the Legends if it was bad? It showed a charging status as indicated above...could it have just been a weak state of charge on “ghost” batteries? Not an auto guy so I'm not sure how to isolate the alternator to check its output. Start truck, disconnect both batteries, alternator should be able to run all electronics in the truck
That sounds like a plan. I take it the first thing to die would be the injectors and associated pumps, for sure telling me it's the alternator? Ha! I'd downsize if I needed that much alternator...
Do load test on both batteries while disconnected and after charging. If either fails, replace both anyways. Make sure all connections are clean and go through fuse box. Then start and test batteries to make sure it is charging. Check and make sure your truck does not have 2 alternators. Some of the ones ordered with a plow package do have 2 ALTS. and you can have weird ass electric problems.
Odds are it is just a bad alternator, unplug the connector on the back of it and make sure the light goes out, if it does the alternator is telling you it is bad turning the light on...Probably the diode in the alternator taking a crap, check the voltage with everything on, blower on high, wipers on high, high beams and see if it is over 13.8, then check for AC voltage across the battery and see if the diode is letting it bleed through. Voltage drop all of the cables with everything on also.
Sounds like alternator (as stated previously). If you have a way to monitor output voltage it would confirm or you could take it to Pep Boys, AutoZone or whoever would run a free scan and it should stand out. Typically you'll get all kinds of crazy codes from low voltage to the ECM, TCM and ABS systems.
Did that, didn't continue with the rest of your suggestions nor did I disconnect the batteries while it was running as dudutzu suggested. Light went out with the unplug, installed new alternator - no light and charging like a mofo. Thank you, Mr. Turner.
