My 1966 Mustang Coupe is not charging the battery. There is less than 400 mv going to the battery. I see that the alternator does not look at that old and possibly replaced by a previous owner. What is the best way to diagnose this problem and then solve it?

If this is happening, does that mean that I should start thinking about replacing all the wiring? I think the wiring may be original from 66.

Any help would be much appreciated. rdambros.

 

Hiya.

You say you have less than 400mV going to the battery.
Does that mean: engine off you have lets say 12V and engine running 12.4V?
if that's what you're saying then somethign _must_ charge the battery. Just not enough, as the voltageis higher.
this could be either:
a) the belt being loose
Check with engine stopped. check for the longest stretch of belt between pulleys. grab it with thumb and index finger.
Try to turn it over it's own axis. You shouldn't be able to turn more than a quarter turn. If you can, then it needs to be tighter.
Then re-check
b) bad ground
with car off run a proper cable (take the black side of a jumplead) and connect it from "battery minus" to a blank spot on the engine (red part of jumplead unused). Make sure the cable is not in any fan or belts way before you start the engine
if you start the engine, do you read different voltage then?

let us know how you get on

 

if it is truely the alternator just isnt sending enough juice to the battery it could be that the brushes are worn out. If the wires are not curroided and worn i wouldnt think that the wiring needs replaced.

 

Opps, try the obvious ... the alternator wires were connected in reverse, so not only was it not charging, but had to rebuild the alternator and replace the voltage modulator. Live and Learn. LOL

 

Good that you found it but there is no such thing as a voltage modulator. I would expect that since you miswired the alt (field shorted to ground) you probably fried the sh_t out of the Voltage Regulator.