Help with overcharging problem 1974 Challenger

I have a 440 in a 1974 Challenger, not sure what year the engine is from, however i am having a major problem: The battery is reading around 12.30 volts and i can get that all the way to the plug at the firewall.
when i check it at the plug behind the carb, it is only reading 10.30, the alternator then starts putting out beyond 25-30.00 volts, blows the fusable link and then the amps drop again and the car is running only on the battery. Have replaced wires, and checked it over and again.
What could cause the overcharge? Is it coming from the ignition? I do not know what to do next. Any help would be appreciated.

thanks,

clay  

i found this 74 D100 wiring diagram that should be really really close to your chassis..

http://repairguide.autozone.com/znetrgs/repair_guide_content/en_us/images/0900c152/80/05/2c/4f/large/0900c15280052c4f.gif


first...   take your volt meter...  set it to 20 volts DC...  turn on the headlights...   touch one test lead to the negative battery post...  the other to the body ... you should have less than 0.02 volts..  if you have more... clean and or add ground wires from the battery to the body..

start the motor..   test from the negative battery post to the engine block.. you should have less than 0.05 volts.. with the alternator charging..   more than that.. you have a bad ground...

more than likely...  the body is not properly grounded to the engine and battery negative...


i would as a install a 8 gauge or 10 gauge wire from the alternator output terminal to the positive battery cable or to the big post on the starter relay... any where that you know the connection to the battery is complete...

i have found

burned out amp meter... that cause this problem...
burned bulkhead connectors that have caused this problem...

i have also found.. messed up and crossed wiring to the alternator and the voltage regulator...

the alternator has 2 small wires on the back... one has positive ignition switches power..    the other is connected
to the side terminal on the voltage regulator connector.....  this usually green wire is pulled to ground by the voltage regulator.. but it does it with pulses...  if this green wire is frayed.,.  or somehow shorted to ground... the alternator will overcharge like you describe..

i would even bet that your alternator diodes are damaged...     alternator repair kits can be had for under 20 bucks..  make sure they come with new diodes..


do the voltage drop test...   for the ground side...    body and engine..

run the thick jumper from the alternator output to the battery ...  see what happens..  post what you find..


you can also do the voltage drop test on the positive side...  reading of less than 0.05 are normal.. if you get more.. you have just measured a circuit with resistance... and that needs to be fixed...  

Thanks for the reply, i am good on the ground and am at a point where i am going to go around the amp meter and see if the problem still exists, that way i can rule out the gauge.

The wiring in this car is more like a 72 than a 74, must have all come with the engine tranny swap.

A friend is helping me tomorrow with checking some under dash wiring, and he has ordered a new ignition switch, i think we are close, i will let you know what happens.


thanks again,

clay