alternator help

[tahitijet]

I have a 4 wire alternator. a post to battery a post to ground, and 2 prongs (1 is supposed to go to battery, and 1 to ignition). If i hook up the 2 prongs one way the motor wont shut off when i reverse them everyting works.
However i'm getting 16-18 volt reading on my gauge.. I'm concerned that this is to high. the gauge is new so i know it's not that and the alternator is a low amp (66 amp i think) model from nappa I think for a mid 80's chevy truck..
Am i missing something here?
thanks

[blackdragster]

Yes you are.
I went thru this years ago. You need a ballast resistor, and I think it feedis the alternator. The output side needs to go the accessory side of the ignition switch, this seperates the output of the alternator from the ignition. Hope this helps. If not try me again.

[GofastRacer]

Or you can clean it all up, spend $33 and convert it to a one wire alternator!. :)

[ONAROLL]

Does the ballest resistor stop the feedback to the distributor or does it stop the overcharging indicated on the gauge?.....Vic

[tahitijet]

ok so a ballast resistor on the small wire (prong) between the alternator and ignition wire (hot when key is on) or on large gauge Pos wire?
the other 2 wires are ground (post) and constant 12v
any specific type ballast resistor?
thanks
and as far as converting to 1 wire i'm done spending money on this project till this winter.. I just want to use it for the few more weeks we have before it gets cold then i'll convert it..

[SoggyJet]

Yes you are.
........ You need a ballast resistor, ......
I think you mean a DIODE. What happens is the current feeds back into the ignition circuit through the wire that energizes the alternator when the ignition is on. A diode allows current to flow in only one direction - to the alternator to energize it.
Doug

[Foggerjet]

I believe you have an externally regulated alt. The internally regulated ones have 3 connectors, 2 male spade conns on the side and a lug on the back that goes to batt. if you wire an ext. reg. to battery voltage it will overcharge as you've described. could be wrong but that's what it sounds like.
fog

[blackdragster]

The ballast resistor is to cure the overcharging (high output voltage). The reason you want the output wire on the accessory post on the ignition switch is so the motor will die when the switch is turned off. If you ty it into the ignition the alternator keeps supplying voltage and the motor keeps running. Hope this helps.