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Discussion Starter · #1 ·
What is the pass/fail test for a voltage regulator? For example, if I check voltages at all these nodes, KOEO, KOER, what values say pass and what values say V.R. fails?
I jumped the F and 3 on the plug that goes to the V.R. and got 16 volts at the battery. so alternator is ok, right? Now I want to check V.R.
some of the posts I've checked are confusing as to which points are being measured (like at the alternator) and I've seen values that should occur to pass, but what if they don't, then what is the source of problem??

7,762 Posts
Think you may be referring to what Peter wrote a couple of years ago. What readings did you get?
I'll try to provide a simplified explaination of how the externally regulated alternator and regulator work here. This explaination starts from a parked car with engine off state.

The brown #4 wire is connected through the light bulb to 12V whenever the key is in the ON position. The other end goes through a set of points in the regulator and then out the F terminal to the field winding in the alternator. So some current begins flowing in the field winding from this connection. The little bit of current flowing produces a weak magnet field in the alternator and also lights the bulb.

When you then start the car, the weak magnetic field from above begins rotating which makes the alternator producing a little bit of voltage. This voltage is fed from the alternator to the regulator on the white #2 wire. This wire connects to a coil in the regulator and turns on a contact when the voltage goes above 3.2V.

Once the contact turns on in the regulator the #3 and #4 terminals are connected together. Terminal #3 is battery power so this puts battery power on both sides of the bulb and turns it off. This means the brown #4 wire should go to +12V. Also, this connects the field terminal right to battery power but still going through the contact.

When the battery voltage goes above a set level, the F terminal is disconnected from the battery power by the contact I kept mentioning. Then the voltage drops and the contact close again. This on-off cycling happens rapidly and is how the voltage gets regulated.

From the above (KOEO = key on engine off and KOER = key on engine running).
F terminal - KOEO = #4 slight voltage KOER = 9-12V typically
#2 terminal - KOEO = 0V KOER = >3.2V
#3 terminal - KOEO = 12V KOER = 12V
#4 terminal - KOEO = F slight voltage KOER = 12V

By 12V above I mean battery voltage, which may be 12V when engine is off but should be 14V when engine is running.

Check the brown #4 wire by grounding it at the regulator. When grounded the light should come on. If you don't have a light then skip this test.

Jumper the blue F terminal to the battery right at the alternator connector. This should make it crank out 16+ volts. If it passes this test, jumper wire the brown wire to the same F terminal and you should be able to measure >3.2 volts on the other terminal. If these tests pass, it is in your regulator or the wiring to the regulator.
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