[chris3353]

Hello all,

1978 f250 400. I finished the rebuild and eliminated the old external alternator and went with a 3 wire GM.

I removed a lot of spaghetti and isolated 3 wires the have power with the key. one choke, one coil and one for the exciter wire.

Problem is the alternator is pushing 12 volts out of terminal 1 (excite wire) and back feeding the other wires. The truck will not turn off.

Sorry i am a rookie with this, isn't terminal 2 to the battery and terminal 1 to a keyed 12 volt source? I did the same swap on my 67 camaro and did not have this problem.

Any advice how to separate these circuits?

Thanks,
Chris

 

[ween]

Wire small bulb (194) as charge indicator on exciter wire. Change exciter circuit connection to accessory circuit.

 

[RODSRUS]

I've had the same problem, the light bulb works, I chose to use a Painless diode kit (30720).

 

[chris3353]

If the white wire (term 1) is not hooked up at all the alternator will not charge?

 

[cerial]

Use diodes they only allow one way flow.

Make sure you do not install them backwards (very easy).

 

[Trinder]

A fully charged battery will have 12.6v, An alternator thats charging will be close to 14v while running. Sometimes alternators will slowly die and be close to 12v while running this is bad.
Also disconnecting a battery while a car is running runs the risk of burning out a perfectly good alternator, or wiring because it spikes the alt into 100% charge and now your computer is running on pure alternator power which is ****ty power (if you look at on a scope). The battery absorbs this and gives a smooth clean 14v.

 

[adantessr]

Use diodes they only allow one way flow.

Make sure you do not install them backwards (very easy).

Perfect solution is the diode. Easy way to check the diode is with a test light. It will only light in one direction.

 

[chris3353]

Installed the Painless Diode from Summit. 10 minutes, Problem solved. Thank you everyone