alternator - high voltage

[hive77]

I had to replace my voltage regulator because the alternator wasn't charging the battery. To be on the safe side, I bought a new alternator and voltage regulator. First, I swapped my old voltage regulator for the new one and everything worked fine. Then I replaced the alternator, after replacing my alternator, a 20A fuse burned immediately after I turned on the ignition. This fuse is between in one of the generator field cables which lead to the voltage regulator. (I have no idea why this is installed there) Then I swapped both field wires. Unfortunately, the alternator now charged with 17 volts. The ominous 20A fuse no longer blew. Because I didn't know why I bought a second voltage regulator and nothing has changed. Today I got a new Wilson alternator from Rockauto, the quality doesn't seem to be the best. Before I replace the alternator, I measured both field plugs. I can measure a continuity between the two field connections, and I can also measure a continuity between the field connection and the housing. Should that be so? Does anyone have an idea where it could fail?
   

340 Dodge Challenger 1973

[Chryco Psycho]

The field is a closed loop , power in & ground out through the regulator which controls the charging rate .
you should Not have continuity between the field connections & ground , often it is just the brushes that are the problem , there should be an isolating washer between the field terminals & the housing , if it is out of position or missing it will ground to the case & can cause it to go to full charge output .
Sounds like the original Alt was good & did not need to be replaced .

[TGGodfrey]

To expand on what was already said.

  To verify the field wires in the harness, One will test 12V (blue), the second one (Green) will test ground.  You should not see continuity here.  The Regulator has two wires, Blue is constant 12V, the Reg case is grounded through the case  As the regulator sees the 12V wire voltage drop, it will provide ground signal to the alternator via the green wire. The 70+ regulator is not an on/off switch like the 69 and older.  Its a little smarter and will regulate the amount of current that is allowed to flow through the field windings of the alternator giving you higher or lower voltage.

  To verify the field windings of the alternator, Two spades you measure continuity across them.  There will be a resistance reading, it should not be zero.  Next, test continuity from the field spade to alternator case (ground).  You should get an open circuit, no continuity.  Do that with each field spade.  If you are getting continuity from field spade to alternator case, next move is to open up the alternator verify the brushes or field spade bolts are not shorting as well as test the armature for shorts to ground.  The armatures do go bad, i have one in my attic that has a constant short in it, at a glance it tests fine but when you spin it, it gets worse.

The Alternator from Rock auto.... send it back, they are junk.

As stated above your original sounds like it was fine, Install it.

Hope this helps you

Terry