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I’ve got a 05 6.0, but a friend is having issues with his 01 7.3 PS. About a month ago he replaced the alternator. Since then the battery light seems to go on & off intermediately. He took the alternator back to NAPA and they told him it tested good. At that point they had him replace both batteries. The next day the battery light started coming on again. Then he replaced the regulator plug, but that didn’t help. He went back to NAPA and they give him another alternator. A week went by with no problems and then all of a sudden the battery light came on and stayed on during a 100 mile trip. Since then it’s been on and off again. He brought it by my house today and left it for me to look at. The first thing I did was to verify they gave him the correct part number. It is the correct number, but is the 6G which has been an issue for rebuilders due to the difference variations in voltage regulators. Since the 6G regulator is actually located inside the alternator (not like the 4G that screws to the outside of slip ring end cover), I could not verify Rayloc installed the correct regulator. It is the gray regulator, but I believe there are at least 2 or 3 regulators that are gray, but have different color covers if you could see it.
After all that, I checked the system voltage with engine off (12.7) & engine on (14.4) and all looked good there although the light wouldn’t come on while I has checking everything. While checking out the wiring I noticed the line side (voltage in) of the glow plug relay was burnt and very hot. I removed the nut and cleaned the stud and ring terminal, then reinstalled with a new nut. I did pull the heat shrink off the ring terminal and wire to verify this connection wasn’t burnt. After doing all that, the stud still gets hot, so I assume the contact is burnt and I need to replace the relay. I don’t think this is his problem unless the contact is welding closed from time to time and draining the system down faster than the alternator can compensate. Has anyone seen this happen? I also noticed his battery cables were not very tight, but as many times as he has had them off you would think at some point they would’ve been tight and the problem go away. Does anyone suggest looking elsewhere? I connected my fluke meter inside the truck so he can at least verify voltage the next time the light comes on.
Last edited by jvest; 04-10-2010 at 10:06 PM.