72 alternator on 78 F engine? (1 Viewer)

[Rockin Lab]

Replaced the alternator on my 78 FJ40. The 78 has a 72 F engine. The new alternator is a 72. Will that work with a 78? The amp for the 72 is 45a, for the 78 it is 50a. Many harness wires lay around unused under the hood (for example, no smog hook ups). What about the voltage regulator. Will that work with a 72 alternator. I am not sure if the vr is 72 or 78, but believe it is 78. Have had the truck two months - previous owner had the F engine installed. He doesn't remember if the vr was for 72 or 78. If I stay with this alternator, should I replace with a 72 vr or 78?

Appreciate any advise. I have a multi-meter, but am a rookie at using it.

 

[Buckwheat]

What alternator did you take off? Was the plug connector on the back the same as the one you just bought? If so, plug it in & see what happens. If not, you'll probably need to change regulators, or get a wiring diagram & rewire the connector.

 

[Rockin Lab]

Not sure what alternator was attached. By the pictures from the part store, it looked like a 78.
The connecters worked. The only difference was the 72 had a harness coming out of the alternator while the one that was attached didn't have a harness. I marked the wires and hooked up the E to E, F to F and N to N to the new harness. It ran and charged ok while idleing. But then I took it around for about 6 miles. Came home and it didn't want to start. Checked the battery and it still read 12 volts. I still need to check the wires to the starter and probably replace the vr. Just wasn't sure if a 72 was compatible with the 78. While the engine was running, I tested the battery and it showed a 12 volt charge. I am new at this and still learning how to use my multi meter to check the system.