Charging system gremlins!

Howdy fellas! Hope I can get some advice on this one!
Car's a '56 Pontiac Starchief, and haven't (before the problems started) changed anything recently. All the connections on I can find are tight too.
The problems started when my alternator stopped charging, and then intermittently was charging. So I figured I'd put a generator in instead (thanks a million Grinderspark!!). I like them better anyhow.
Generator output was fluctuating between 12.3-16.8V, but the ammeter in the dash was showing no charge....no discharge either, but no charge. I fought with it awhile, and finally got frustrated and put another alternator in. This alternator tested normal on the test stand at the parts store. Put it in and all seemed ok till I drove it!
As soon as I hit about 3000 rpm's and about 30 mph the speedometer cable started making noise and the dash and headlights started flashing.....ammeter was going crazy too. Different symptom, but same conditions as when the first alternator ****ped out. I have no idea where to begin here! Does it sound like the speedo cable is flexing under the dash and causing a short??? No sparks or smoke from under there. Positive battery cable is new (thought it might have been the problem in the first place) and negative battery cable looks pretty good too.
Any ideas????
Thanks!
Johnny

 

Hmm...the genny was doing its job, but sounds like the regulator wasn't controlling the output correctly. 16.8V sounds a little high, like unregulated high. Could be your ammeter wasn't hooked up correctly from all the swapping, might be why it was showing nothing.

 

Check the body to frame and body to engine grounds if there are any. If not add some.

 

The ammeter wiring is basically unchanged......the batt. wire to the stock regulator is where the alternator + goes, so I just used a terminal on the end of the alternator wire to connect to the original (ammeter) batt. wire on voltage reg. It's a good solid connection and it worked fine for two years or so.......
If it had a real nasty short somewhere, that would cause a rapid discharge wouldn't it? I'm thinking that the voltage was so high because it was feeding a short somewhere......no idea yet though!
I do need to check the body/engine/frame grounds. I have a nice heavy one from the battery to the engine, but should probably add the others.