'71 fj40 - Alternator Not Charging Battery but Tested Good. (1 Viewer)

This site may earn a commission from merchant affiliate
links, including eBay, Amazon, Skimlinks, and others.

Joined
Oct 4, 2018
Threads
59
Messages
269
Location
Marietta, GA
The wife and I headed out on our longest trip since I got the truck running yesterday. The truck was running the best it has since I have owned it and I was smiling so hard I got a headache. We stopped at the beer store about 5 miles from my house. When I got back in the truck, beer in hand, it would not start - sounded like a dead battery (slow cranking and then just clicking). I looked under the hood, wiggled a few wires at the starter, battery and alternator and it started. We drove it about 15 more miles, hung out with some friends.

When we started back home, it was getting dark so about half way home, I had to turn the headlights on. We stopped again to grab some food about 3 miles from home and the truck was dead. We were about to jump start it and got it home. The starter, alternator and battery are all new within the last 6 months. Some observations and steps taken so far...
- ever since I have gotten it running, the ammeter pretty much always stays in the middle except when I hit the brake pedal (drops a little) or turn on headlights (drops a lot). The needle never moves toward the +30 side.
- I inspected all wires from alternator, starter and battery and they all appear to have solid connections and the grounds look good and clean.
- this morning, I pulled out the multimeter and the battery was at 12.2 volts. I put a charger on it for a while and it eventually tested at 12.61 volts
- I cranked the truck and hooked up the multimeter to the + and - on the battery and was reading 12.2 volts. I then put the multimeter on the white/blue wire at the alternator and it was reading 12.13 volts.
- Assuming I might have a bad alternator, I took it out to have it tested. It tested good....

I am at a little bit of a loss and any thoughts are appreciated.

- Farrell
 
Voltage regulator...pretty sure you should have an external version.


I agree usually get higher voltage when running. Right after starting amp meter should go up into the plus side to recover the drain the battery from starting.

I would also check the ground wire on the block. Wiggling wires to get it started would be something other than voltage regulator.
 
Try following the steps we took in this thread HERE . Make sure your Engine fuse is good. The Ammeter is a great diagnostic tool if you understand what it is telling you. It is showing the directional flow of electrons and how fast they are flowing. If it is in the middle no electrons are flowing. If it is in a + direction then electrons are flowing to the battery. The further the needle is in the + direction the more electrons are flowing. If it is in the - direction the elcectrons are flowing away from the battery.
 

Users who are viewing this thread

Back
Top Bottom