Battery or alternator issue?

[Sucretrou]

So this a couple weeks ago I was taking a trip from New Mexico and heading home. About a 10 hour drive. 2 hours in my truck dies. I find out what’s wrong and basically my alternator was done with. Bought a new one and installed it myself, granted I don’t know too much so I called a buddy and asked him to guide me on how to do it. I did it and I FaceTimed him he said it looked good. Went to the oreilly so they could charge my battery. They said it was bad. So I got a new battery too. Put it in so I got a new alternator and new battery. The new alternator had a different pulley up front so I used my pulley from the old alternator and just swapped it onto the new one. I started driving and I went good for about 6 hours. Then my headlights started dimming since it was nighttime and I checked my battery gauge and it was ready very low around 8 already in the red zone. So I pulled over and I turned it off. Tried turning it back on and it was dead. Completely dead, no response whatsoever not even a click. So I got a jump and I ran it for another 5 minutes. Same issue. I ended up getting a buddy to tow the rest of the way home. I got home and jumped it but it will only stay on for all of 2 minutes. I did notice the belt up on the alternator pulley was loose when I checked so I tightened it thinking it was the issue. Didn’t change anything. Then I noticed one of the battery cables or whatever they are called that hook up to the alternator wasn’t completely tight onto the alternator. But it didn’t really wiggle. Like it’s snug on there but the nut that holds it in place isn’t ALL the way down. So now I haven’t figured it out on what the issue is. The wiring had all been redone when I was in New Mexico so I don’t think that’s an issue. But yeah every time I jump it it will go up to the 12 on the gauge but as soon as I unhook the jumper cables it starts draining and ends up dying. If I can get some help because I truly am at a loss here. Thanks

 

[Crispy]

Check the output on the alternator while the truck is running for those 5 minutes. Not on the gauge in the cab but with a multimeter at the battery, if its around 14.4 then you are good. If the alternator was a reman it may be bad and wouldve taken out your new battery with it. Both should be covered under warranty. Just make sure you put the pulley that came with it back on and dont tell oreillys you swapped pulleys.

 

[1987 GMC Jimmy]

I would actually test alternator output right at the back of the unit just to be safe. It's sounding to me like a defective alternator.

 

[smoothandlow84]

Start the truck. With the truck running at idle disconnect the positive terminal of the battery. If the motor dies, it's a bad alternator. From what you described, it's more than likely a bad alternator. When the engine is running, it turns the alternator which charges the battery. If the alternator is bad, it's not charging your battery and anything electrical is depleting the battery (headlights, stereo, turn signals, horn etc.). The same thing happens if you loose the alternator belt or drive without one.