74 duster electrical problems
The way I do it is "test around it." Some may think my method is "around the bush" but here's the thing. it (for me) is always better to check wiring if at all possible "under load" which seems to do a better job of showing up bad connections than does resistance (ohm) tests
First, a simplified diagram of the charging system:
Essentially what you have there is the "ignition run" (blue) feeding the VR IGN terminal and one of the alternator field terminals
The VR must be grounded.
The IGN feed to the VR powers the circuitry and also acts as a SENSING point.
The VR controls alternator output by "controlling the amount of grounding" on the green field wire.
So first check the IGN terminal of the VR or as close as you can get, everything hooked up, and key on / engine off. This voltage should be within .2--.3V of the battery.
Next, check "full charge."
You can remove the green field wire at the alternator, and ground that alternator terminal. Easy bring up RPM and battery voltage should rise. Depending on state of batt charge, it might come up a lot. Try to keep it below 16V
You can also check the VR harness wiring by starting with everything wired normal. Disconnect the BLUE wire this time at the alternator and ground it. Now pull the VR connector and devise a way to jumper around the two terminals in the plug. A couple of machine screws the right size will work.
Again, this should cause "full field. or full output.
If this works, hook everything back up and see what you have. "Work" the VR connector in/ out and check for corrosion. See what you have for charging voltage, with engine warm. If it's high, above 14.5, I would again check for voltage drop from battery to VR.
Another way, with engine running, is to check battery voltage. If it's high, check voltage at the ignition ballast wire coming from key. If this is "normal" (13.8--14.2) then the VR is OK and is merely suffering from low supply voltage-------voltage drop.
The other "fly" in this soup is poor quality modern day replacements. "It used to be" that NAPA "Echlin" or "Standard Blue Streak" used to be good stuff. Does not seem to be that way.
These VR don't fail very often. The one on my car is used OEM. The one I used to have on my old beat up Landcruiser (Mopar power) was the same USED one on there from 74 something to whenever I stopped driving it. Last time it ran, charged just fine. That regulator is probably an early 70's OEM and I still have it "somewhere."
The way I do it is "test around it." Some may think my method is "around the bush" but here's the thing. it (for me) is always better to check wiring if at all possible "under load" which seems to do a better job of showing up bad connections than does resistance (ohm) tests
First, a simplified diagram of the charging system:
Essentially what you have there is the "ignition run" (blue) feeding the VR IGN terminal and one of the alternator field terminals
The VR must be grounded.
The IGN feed to the VR powers the circuitry and also acts as a SENSING point.
The VR controls alternator output by "controlling the amount of grounding" on the green field wire.
So first check the IGN terminal of the VR or as close as you can get, everything hooked up, and key on / engine off. This voltage should be within .2--.3V of the battery.
Next, check "full charge."
You can remove the green field wire at the alternator, and ground that alternator terminal. Easy bring up RPM and battery voltage should rise. Depending on state of batt charge, it might come up a lot. Try to keep it below 16V
You can also check the VR harness wiring by starting with everything wired normal. Disconnect the BLUE wire this time at the alternator and ground it. Now pull the VR connector and devise a way to jumper around the two terminals in the plug. A couple of machine screws the right size will work.
Again, this should cause "full field. or full output.
If this works, hook everything back up and see what you have. "Work" the VR connector in/ out and check for corrosion. See what you have for charging voltage, with engine warm. If it's high, above 14.5, I would again check for voltage drop from battery to VR.
Another way, with engine running, is to check battery voltage. If it's high, check voltage at the ignition ballast wire coming from key. If this is "normal" (13.8--14.2) then the VR is OK and is merely suffering from low supply voltage-------voltage drop.
The other "fly" in this soup is poor quality modern day replacements. "It used to be" that NAPA "Echlin" or "Standard Blue Streak" used to be good stuff. Does not seem to be that way.
These VR don't fail very often. The one on my car is used OEM. The one I used to have on my old beat up Landcruiser (Mopar power) was the same USED one on there from 74 something to whenever I stopped driving it. Last time it ran, charged just fine. That regulator is probably an early 70's OEM and I still have it "somewhere."
