Original poster: GTM



Fastest 2 minute Alternator circuit check for charging on 1G & posibly 2G. I devised this test when troubleshooting an idiot charging light glowing when still charging correctly back in the mid 70s. It's still not common place but can be found in some publications.


Assumes a reasonably charged battery though not an absolute for most of the tests will need only about 6 volts to activate the test light. The drive belt should be properly tensioned. At the very least try to spin the alternator cooling fan with fingers, should not slip.


With a proper probe type test light connected to ground and the key off and done at the rear of the alternator.


1) test the large B+ lead (White or possibly Red wire) and the terminal on the back of the alternator. Must light.


2) Test the Yellow wire at the 2 wire plug on the back of the alternator. Must light.


3) Test the Black with White trace wire (BW) at the same plug. Must _not_ light.


4) Test the Black with White (BW) as above but with the key _on_. Must light dimly.


5) Start engine, test the BW and slowly increase engine speed. Light must increase in brightness as RPM increase to 2000.


Conclusions:


If #1 failure then the main 80 or 100 Amp fuse is burned or an open circuit at battery or fuse connections.


If #2 failure then 30 amp fuse connected to Yellow wire is burned or "Sub Fusible Link" burned.


If #3 failure (light is on) then a short exists between the Ignition Switch OFF position and the Alternator plug.


If #4 failure then "Alternator Relay" coil is burned or an open circuit between the alternator terminal plug and the Ignition Switch.


If #5 failure then the alternator has an internal problem.
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It is not the intent of this article to discuss possible failures within the Alternator for that is a very lengthy process and increased skills plus tools. I may put something up at a later time when I have a spare to refresh my memory.


Here is one more quick test but requires an "inductive" type ammeter which you just lay over the wire and take readings. It does require a good fully charged battery. Turn the headlights on high, turn the heater fan to high, turn rear window defroster on, and the key to on. Leave it this way for exactly 1 minute, turn everything off, start the car and then with the inductive ammeter check the alternator B+ wire while increasing the RPM to 2000. The charge rate should be approximately 75% of the alternator rated capacity thus if 100 amp you should see 75 amps which then starts to taper off.