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Tail light problem


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Most likely a bad ground, or grounds.    This is an old car, make sure the previous owner did not delete any grounds.  The grounds could also just go bad, because the car is 46 years old.

If you have a volt meter, use a pin to make a tiny hole into the black wire on each lamp, and connect the positive lead of the volt meter to that.  Get a long wire, connect it to battery negative, and back by the taillights, measure the voltage between the black wire, connected to the lamp sockets and the wire coming from battery negative.  This should be less than .5 volts, but ideally less than .2 volts

The black wire coming from each lamp holder must have a good connection where the wires "Y" together.  They have to have a good connection to the body of the car.


This is based on my 521.  There is a ground wire from the negative battery cable connection on the cylinder head, that goes to the alternator frame.  There is a second black wire that goes from the alternator frame to the voltage regulator, and connects to the inner fender, to ground the cab, or the body of the vehicle.  These engine room ground wires are very important, because if they are missing, or go bad the lights grounded by the body of the car try to ground through the throttle linkage, and screw it up.

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