originally published as I Thought It Was Only Me in the January 2000 RootesReview:

I just discovered that my wiring harness (aftermarket) did not match the wiring diagram in the shop manual (which I believe is the way the car is supposed to be) and, therefore, that the ammeter has been hooked up incorrectly for five years. The harness had wires coming out in all the right places to match up with the connection points as per the wiring diagram, but the wires did not travel where they were supposed to inside the wrappings. Although the old hookup did read out changes in charging currents, it was not telling the complete story. To indicate properly, all power (other than the horns, map light, cigar lighter, starter motor) needs to go through the ammeter. Three simple tests can tell you if all is as it should be in your car. (These apply only to cars with generators and working ammeters).

  1. Turn the key on. The ammeter should go slightly negative. If not, the power to the ignition switch is not going through the ammeter.
  2. Next, with ignition switch off, turn on the headlights. The ammeter should go very negative. If not, the power for the lights is not going through the ammeter.
  3. Lastly, disconnect the three brown wires (two terminal ends) from the terminal at the voltage regulator and separate the two terminal ends so they don’t touch each other. If all is wired correctly, your lights and ignition switched components should not work. If either of them does, they are getting power from somewhere other than where they should be.

ammeter wiringThe fix will depend on which, if any, of the above problems you have. Above are sections of the wiring diagram from the Shop Manual in the area of the ammeter/voltage regulator. The one named “As it should be” is as it should be with a correct wiring harness and an ammeter/voltage regulator.

The one named “As mine is now” is as mine is now given that the aftermarket wiring harness did not match the factory wiring diagram and I changed some things to make sure the ammeter would read properly. The differences in the “As mine is now” are in the way the wires from the 1/2 fuse block (map lights, horns … see full diagram in the Shop Manual) hook up to the voltage regulator rather than the solenoid as it should (this was a shortcut the wiring harness manufacturer took to save wire) and my adding a wire from the light switch to the down stream side of the ammeter to get that current to go through the ammeter. The end result (with my wiring harness) is that there is an unused brown wire out of the harness bundle under the dash that used to go to the light switch. (Other embarrassing topics coming up: improperly wiring the wiper motor switch, not lubricating the pilot bushing-to-trans shaft interface, windshield wipers that won’t turn off, massive water leaks and morel)

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