Generator bad or regulator ?

[tbh726]

All not sure if it is related, i screwed up and left the service switch on and it drained my batteries. i put in a minor charge just enough that it started the Mutt and figured my generator would charge the batteries up, i went for a short drive 4 or 5 miles and it sputtered and then died, batteries were dead. i got it back home and put the charger on the batteries overnight and it said they were fully charged (pretty sure they are damaged since drained so low). i easily started the Mutt up and it was running fine. i then pulled the negative wire that is connected to the frame to the batteries and the engine died immediately. Put the cable back on the battery and the engine started right up.

tried to do some research and figured it points to the generator, but also saw it could possibly be the regulator. Any ideas? is there another way to test or determine what is not working? i have a 77 A2 with a 60 amp generator, it is also a AMG mutt.

Also wondering if i keep the batteries on a float how long can i drive it with charged batteries? 10 miles more? at least till i get whatever fixed.

thanks for any help
tim

[rickf]

If you pull the cable with it running on an alternator the chances of frying the regulator are quite high. That was an old trick that worked well with generators but with an alternator the spike when removing the cable will 75% of the time take out the regulator. In your case it sounds like this was already bad before you did that. Leaving the switch on will feed battery power to the alternator but I doubt that is what happened. Charging with the cables connected is also not recommended since it puts upwards of 30 volts into the batteries and even more if the charger has a desulfation mode. Take the cover off of the wire access on the alternator and turn the switch to on and then see if you have at least battery voltage at the #568 wire. If you have voltage there start it up and see what voltage you have on the #5 wire. If it is the same as the other wire the alternator is bad, most likely a bad regulator. Southern Automotive has all of that stuff to repair these alternators.

https://www.southernautomotive.com/catalog/index.php/