I recently had a change happen in the charging voltage at the battery. Its now reading 15.3v. I pulled alternator had it tested, its good, then tried a different voltage regulator same issue with 15.3 volts at battery. Any suggestions where to look next?

Thx Mike

Try running a wire from bat neg to the reg.It might be losing ground.Have the batt tested also.Ive seen bad ones up the charge.Rocky

therocks I will try both those suggestions....keep them coming guys.

I don't think 15.3 V is a problem?

Mine has been charging at 14.7-15.0 volts for years.

I would also measure voltage at the sensing line and compare it to battery voltage.
a drop there could also cause an over charge.
be sure to use the ground at the vr for the complete circuit, not the battery neg for the sensing line.

What wire is the sensing line?

there are 2 wires to the vr, regardless of which type.
one of them will read 12 volts with the car in run(not running).
the other will not read anything if it is the new style(since it is unplugged) and the old stlye will read something like 3 or 5 volts.

not sure what color, since you didn't mention what car.

Mine is 1970 Cuda. i have the Mopar performance distributor with Silver ECU and black voltage regulator with restoration wire harness for Electronic ignition.

So I pull the VR connector, then measure voltage of the wire with key in run position and compare to the battery voltage. If they are same, that is good, if not?

early (1 field wire/mech reg) or later (2 field wires/electronic reg)? A low battery will require that high & that is too high (for a charged batt) but you said this happened all of a sudden? A batt can go bad & want a high rate. To elim this can you sub in another batt for 5 minutes? I would put it on a fast idle & check voltages at the batt and the alt and the blue sense wire AT the reg and voltae drop between reg case and batt neg post on low scale (tenths). k.i.s.s I'd be inclined to think reg or voltage drops & more reg cuz it happened all of a sudden if I'm reading that right. sumpin ain't makin sense here on the symptoms especially with the alt and reg testing good & you'd think r&r ing the reg would confirm its' ground. Break out your meter!

so if the voltages are not close, then you have high resistance somewhere like the bulkhead connector.
typically that is what has to be taken apart and cleaned to fix that.
or others run a relay, so that key on trip it on and supply power directly from the battery to the vr.

I agree that you should check out the battery too just incase. either could make this happen.

I have #2 the two field wire with electronic VR. I do have a second battery to use and will try that first.I did run a ground wire from the alt to the VR and that had no effect. I also cleaned up all the grounds including VR to firewall.

I suspect the battery now.....its 4 yrs old.

Thanks to all, Moparts is a great place to get help.

You subbed in another electronic reg for the electronic reg that was in there & no change? I'm gonna go out on a limb & say that both regs are bad . Holler how it turns out

The VR regulates the voltage by varying the ground to the green field wire, if the green wire shorts to ground anywhere between the alternator and the VR (along the valve cover is common) the alternator will put out a high voltage.

Also, most testers fully ground one field terminal so an internally grounded field will show OK on the tester. Try swapping the field wires at the alternator to see if that makes a difference...if not, check for a shorted green wire.

Rapidrobert, very possible you are right, I do have a third VR i can try. I want to swap out batteries first and go from there.

John, I had the alternator tested by a rebuilder, I explained my problem to the rebuilder, hoping he tested it to eliminate the alternator as the problem.

When it's running (carefully) check the voltage between the battery + terminal, and the blue wire at the alternator.

I'd wager you'll read ~0.8v there. If so, that's your problem, and like mentioned earlier, you have too much resistance in the blue wire between the alt and the battery.

Check your major hot wires. The big heavy ones like the one on the steering column. Check all the connections. I had the same problem with my Challenger years ago and it was a bad connection at the column harness to the main harness connection. Bypassed it and cleared it all up.

I changed battery and it dropped to 14.8v running, the engine was still relatively cold and off fast idle. I will further check the sense wire to see what is going on there. Thanks for that suggestion.

When trying too sort out charging system issues it is best to have a fully charged battery. Sounds like either your battery was low or is weak. Might want to charge and test it.