Howdy,

Welcome to the Brickboard. Don't worry too much about asking questions that have already been covered. It happens daily and most folks here will either answer your question or direct you to the answer.

Between the fuse and the tail light panels are the switch on the pedal and the Bulb Failure Sensor. When you checked for 12V at the rear, was the pedal depressed?

The BFS is the most common source of problems. It carries all the current for the lighting system except the low beams. After a few years it gets resistive. For some reason the engineers hid relays like Easter eggs. I am not sure where the engineers put the BFS on the 1990 models. Someone here will be able to direct you to it.

The next most common failure is the ground point on the rear for the bulbs. But, if you have tail and backup lights that is not the problem here.
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Mr. Shannon DeWolfe -- I've taken to using mister because my name misleads folks on the WWW. I am a 52 year old fat man. ;-)