Alternator Gauge Drops when Stepping on Brake

[ritchyt122]

I have a '69 Coronet with a 383 and a new battery (automatic trans).  The car starts-up and runs, but when I step on the brake, turn on the headlights, etc. the alternator gauge drops quickly from the middle down halfway to dead.  When I release the brake/turn off the headlights it moves back quickly towards the middle.  Possibly related, when I turn on the turn signals, they light up (inside and out) but they do not blink.
Does anyone have a suggestion on how to fix these issues?
Thanks!
richard.tyre@gmail.com

[azz7772]

I have a '69 Coronet with a 383 and a new battery (automatic trans).  The car starts-up and runs, but when I step on the brake, turn on the headlights, etc. the alternator gauge drops quickly from the middle down halfway to dead.  When I release the brake/turn off the headlights it moves back quickly towards the middle.  Possibly related, when I turn on the turn signals, they light up (inside and out) but they do not blink.
Does anyone have a suggestion on how to fix these issues?
Thanks!
richard.tyre@gmail.com

I would start simple and check the battery and see if it passes a load test also check battery cables then if thats ok then check alternator out.if your battery is new i would suspect the alt. but i have seen alot of faulty parts from new your signal light problem sound like the flasher is toast not a big deal and should not affect the main problem

[Dartsport]

Check the turn signal flasher?

[sweatybetty]

check your ground wire from the battery to the block then the ground from the block to the body/frame. alot of times these are missing or not a clean tight connection. even better would be wire from the battery negative right to the body.

[Jim_Lusk]

The "D" is discharge. All it means is that the alternator is not putting out enough at idle to power everything so it is pulling from the battery. That's fairly common with the low amperage alternators these cars came with.

[davemac]

If you cannot drive the car to Autozone where they will check it for free, I would pull the alternator and take it to Autozone.
You can home test the alternator by disconnecting the positive cable while the engine is running.  If the alt is bad the car will quickly die out

It is also possible that you have a bad flasher relay.

Cheep stuff thats easy to fix.

[Sixpak]

If no one has ever fixed / cleaned the connectors at the firewall then I'd bet that's where at least part of the problem is. Wiring connectors from the battery to the ammeter and from the alternator to the ammeter corroed, maybe even burnt. EVERY old Mopar I ever owned needed them cleaned and greased, or replaced/bypassed at the connector.

[robgoudy]

You will need to do a bit more diagnostics. First check the battery voltage while running....sounds like low voltage. It amazes me how well the old Mopars will run on very little voltage, especially if you still have points. Sounds to me like an alternator....But there are so many other possibilities. The hot lead from the alternator can cook off if the regulator gets funny. Could be brushes in the alternator. Check for a sticky regulator, especially if yours is still mechanical. Sometimes the braided ground strap will stop flowing current if it gets the green-weanies. And don't forget those battery terminals. There are just so many possibilities, especially when your dealing with the electrics on a 37 year old vehicle.