Hey all, I have an alternator off a 1992 F-150 extended cab 4.9L that I swapped into My 1946 ford truck. I grabbed the harness off the 92', it only had 2 wires hooked into the donor harness, so I thought a simple hook up. I hooked 1 wire to battery side of solenoid, and 1 wire to ignition switch. Now it works but it gets really hot running or not and drains the battery when not running. The wire I ran to the ign. switch doesn't have a resistor or battery light but I ran it through a push button switch that only connects while the button is pushed. If I connect the battery cables and don't start the engine or push the button and let it sit for about half an hour the alternator will be almost to hot to touch.

What I am wondering is , is My wiring wrong or is the alternator bad? I've read about alternator fires and don't want to burn My truck to the ground.
Any help would be appreciated. Thanks, Dan

 

Did you reverse the wires?

 

Here's how it should be hooked up. If it still gets hot and drains the battery, the alternator is probably bad. Usually a shorted diode inside the alternator will cause this.

 

Thanks for the replies. Big wire to battery, small wire to ignition, The truck was previously positive ground 6 volt, but when I switched to 12 volt I changed to negative ground. It is hooked up pretty much the same as the diagram. If I bring it in to a parts store for testing, would a shorted diode show up as bad? Thanks, Dan

 

Yes it should.

 

Why do I suspect that the wire from the ignition is now negative (ground) when it is turned "off"?

 

I don't know why You would suspect it going to ground? The positive battery cable goes from positive on battery to one side of solenoid where the main power supply wire then goes to the battery pole of ignition switch,(universal aftermarket switch) then the smaller alt. wire is hooked to a normally open push button switch, and then to the run pole on the ignition switch. The negative battery cable goes from negative on battery to stud on firewall.
As far as I know ignition switches are open in the off position, so the small alt. wire should be open with key in off position whether the push button is depressed or not. ( open switch as far as I'm referring = ___/ ____)

 

When it is a conversion to reverse polarity, unless you have all the engineering documents, you have no idea of what is really there.

Don't forget.. lots of mods, fixes, etc. got done to this thing in the interim years, all undocumented.

 

Converting from positive to negative ground is not difficult. The lights don't care, the starter doesn't care, the wiper motor doesn't care. The radio needs to be switched out for a newer one or converted, and the charging system needs to be converted to something newer, and the coil needs to be switched out and turned around.