Please help!! A week ago my battery light came on. Load tested batteries to find 1 bad battery. Replaced bat and light was still on. Tested Alt and it was bad. Replaced Alt and all was good. Until yesterday. Truck started slow and ABS light came on when i went to park. After truck was off for 45 minutes came back out to start and "click, click, click, click". Used booster pack to start truck to get it to the shop. Truck killed 4 times over a 3 mile trip. Disconnected and Charged batteries over night. Reconnected the next day and truck started fine. Let truck sit most of the day to see if voltage dropped dropped and bats read 12.9 at end of day. Started truck and voltage from alt and bats then read 12.5ish. Once truck was turned off bat voltage started coming back up to 12.8ish. What could cause this? Also checked fuses and fuse 31 "Transmission Range Sensor (AT only) then to starter relay coil, 4x4" lit test light when starting truck then test light went off as expected. However when i turned the key off and checked this fuse again the test light showed a 2.6V draw. Again what would cause this?

 

Can run into problems if only replacing half the battery. The older one probably has some sulfation built up on the plates.

 

bad NEW alternator.
bad battery connections.
bad ground connections.. at frame
bad battery cables.
bad wiring going to/from Alternator

you do not show the location you live... so winter salt .. Rust... it is 13 years old.

 

Red herring, don't worry about it.

Another red herring, don't worry about it.

What's important is that your alternator isn't charging. Just because you replaced the alternator doesn't mean its good, especially if it was a rebuild.