I have a 1977 Dodge W200 with a 318 V8. The battery will not charge when the vehicle is running. The battery is new and I can charge it with jumper cables or a trickle charger. When the vehicle is running the voltage drops to 11 volts and does not recover. I have had the alternator tested. The alternator was producing 15 volts. I replaced the voltage regulator again with no effect. When I put the alternator back on the vehicle and start it I am getting less the 12 volts at the battery.
Check the voltage on the large terminal on the back of the alternator with the engine running. If it shows 13.5-14.5 volts at the terminal there’s an open circuit between the alternator and the battery.
Tester
If your Dodge has an Ammeter on the dash, check the connections to the gauge. I once had a problem with a Dodge van that would charge the battery very slowly although the alternator was good. I was getting a 2.5 volt drop across the ammeter. IIRC I replaced the gauge and celaned the connectors of the wire and the problem was cured.
Hope that is what it is.
On the drivers inner fender is mounted a starter relay. The positive battery cable is connected there. The big, heavy red wire coming out of the firewall connector block is the alternator charging lead coming from the ammeter in the instrument cluster. If the ammeter is burned out, it opens the charging circuit like a blown fuse…Connect a jumper from the heavy charging lead on the alternator to the post on the starter relay where the battery cable connects. Keep it out of the fan… You have now bypassed the ammeter and its wiring. Start the truck and watch the voltage across the battery. It should slowly climb to 13 volts or a little more. Use at least 12 gauge wire for the jumper…Try this first…
If it fails to charge with the jumper in place, post back and I’ll tell you how to “full field” the alternator, a test that bypasses the regulator…
Thanks fellas…First thing tomorrow morning…Ill let you know how it works