Alternator Question

I second aboves, w/ more details:

My '69 Dart had a single field wire (round alt, 30A?). The other field connector grounded thru the alternator frame. The voltage regulator applied 12 V to the field - on/off in original mechanical solenoid type or 0 to 12 V proportional (I think) for later upgrade electronic ones (made to look like original). I once thought the alternator was bad, but the new one acted the same. I fixed it in the Auto Parts parking lot and got a refund. It wasn't getting a good ground thru the frame (alminum is bad for that). I ran a separate ground wire to the 2nd connector.

My '82 Aries (square-back alt) used 2 field wires, one was constant +12V and the return controlled by the electronic regulator. They did this because easier to regulate on the low side. It also cures the problems of relying on the frame ground.

Look close at your field terminals (brushes). For your car, the one without a wire should not have an insulator and should clamp against the aluminum frame. If so, remove and sand the aluminum. If isolated and has a spade terminal, that is OK. Run ~14 awg wire from it to a good engine ground. That is better than relying on the frame ground anyway.

If your ammeter works, you should see when the alt is charging or discharging. If the alternator isn't working, you will just barely see the needle leaning towards "D", more if the high beams are on. You can over-ride the regulator by disconnecting the field wire (marked "F", small bolt I recall) and connect it to the 12 V battery post. You should then see the ammeter go strong towards "C". If your ammeter is broken, the alternator can't charge the battery (all output goes thru ammeter I recall). To check, measure the resistance from the large wire at the alternator (disconnected) to the battery +12 V, or between the two bolted terminals on the firewall (disconnected). I would guess <10 ohms. Check your wiring diagram first since from memory. If you don't have a multimeter, they are $3 at Harbor Freight. I keep one in every car.

Later cars dropped the ammeter and put in a stupid "low battery" light. By the time that comes on, you have big problems. That stranded me multiple times in my '82 S-10 and Aries. I tested the Aries by breaking the large alternator connector in the engine compartment and putting a 100 A meter in series. A classic hobo test is to start the engine and disconnect the battery. It should run on the alternator output alone. This was claimed to possibly damage later electronics ('80+). You don't need either since you have an ammeter built in.

I think the original 30 A alternator should be fine. I think some were 40 A, and JC Whitney long sold an upgrade kit (field coils & diodes?) that gave more. The later square-back alternators should bolt-in. I think rated 70 A. The one in my Aries fried the diodes every year, always the set "hanging in the air" not the ones bolted against the frame. An auto electronics shop confirmed my experience. The square-back is great for looking to see if they vaporized again. I got good at taking the alternator apart underneath the AC compressor and replacing just the diode bar. By cutting slots in the diode bar for cooling I got them to last 2 years. The 60's alternator with big diodes pressed into the frame can't be beat for reliability and they look better.

I recall mention that later alternators (Denso?) can bolt in, but never tried. Not sure if some came with a V-belt pulley or if you can swap pulleys. Also, you would need to change connectors. They are small, light, reliable, and put out ample current (100 A?), but 30A should suffice for you.