Hi all, I'm having some trouble with the alternator on a 68 charger. I just had the motor rebuilt for my dad and since its been back together it isn't charging. The alternator is a stock replacement from NAPA. I took it back to them and put it on the test machine and it showed 70 amps. Currently with the car running I have:

12.2 volts at the alternator power lug
0 volts at the field plug
2 volts on one side of the voltage regulator
11.7 volts on the other side of the voltage regulator.

There alternator is grounded and shows good continuity back to the negative terminal of the battery.

The field terminal also shows continuity back to the ground.

The car is a 318 car and is stock other than a switch from points to a pertronix electronic ignition and the bypassing of the ballast resistor.

Any ideas? what should I be seeing at the field terminal?

Thanks!
-Jon

I have the similar setup on my 67 Belvy II - 318 car......kept the ballast resistor. Hooked Pertronix hot wire to the passenger side terminal of the resistor - to get 12v in the run mode.

(1) make sure the reg is grounded (2) disconnect the green wire from the alt and the VR and replace it w a jumper lead w alligator clips on each end & if no charge the VR is bad & I'd highly consider an electronic replacement. Someone here on the board has an electronic one that looks identical to the electromechanical ones including the black cover for $25 to your door or your parts house has a "wells" brand that is electronic but does not look original if that is important to you

The fact that it happened at the same time as the eng swap confuses a persons' diagnosing but sometimes parts fail at the most inopportune moment w no rhyme or reason & this time it happened at the same time as a major repair. If you have switched 12V at the "ign" VR terminal (within several tenths of batt voltage is ideal) then the VR only needs to send the reduced voltage out the other (field) side (not sure what is a correct voltage reading on the green wire and as you know it does vary) straight to the (1) field terminal WITH the alt and VR ground having good continuity back to the batt neg post so it is sensing the correct voltage.

Well its pretty pleasant out tonight so I went out and ran a jumper from the green 2V side of the VR to the field of the alternator with no result. I disconnected the wire from the same side of the VR while doing the test. was that the right way to do it?

So is the field supposed to have a voltage to it? I'm assuming yes? If so, why would mine be showing continuity to ground?

Thanks!
-Jon

Just a recap, 68 Mopar uses only one field wire alternators, none made anywhere near 70 amps..
I think 37 amp was the correct number..
Did you upgrade or change alternators during the build?
Paint under the regulator will cause it not to ground or work correctly, engine bay repainted.?
And the most common is the bulkhead connector gets burned and wont make a good connection, take the connector off the bulkhead and give it a visual.

take the feild wire off the alt- then check the alt terminal for the feild wire to ground- there will be some resistance due to the end of the field coil to the case of the alt.- simce it was checked out ok- I think it is good. the reg. sends out voltage to the field coil to excite it to produce power.use a volt meter accross the battery and wtach-then with the field wire off and the car running- take a jumper wire from the large power wire and touch it to the field wire- you should be producing power. if yes with about + 13-14 volts at the battery- the alt and wiring is ok- look at the reg. make sure it has a good clean ground behind the mounting bolt.
Something extra to do is to add a braided ground strap from the reg.'s mounting bolt to the rear head bolt of the engine.

John Mac