Toyota Repair: Tail light fuse is blowing and loosing cluster illumination

Question
Hi there, I have a 1993 Toyota Tercel. I have experience working on Heavy Duty Diesels but not so much in this field. The 15A fuse in the fuse panel bellow the dash keeps popping . When it does I loose marker lights, running lights in the rear, and cluster illumination. The fuse will pop as soon as the head light switch is turned on in the first position. Found a short in the line that I fixed. Then about 10 miles later it popped again. Wondering if there might be a relay or a solenoid that was damaged previously? Where do I Start from here?

Answer
Hello, as you probably know this 15 amp fuse supplies voltage to the dash illumination as well as the tail lights and marker lights and back up lights, since the fuse blows only when either the switch is in the 'parking light' or the headlight on position we can rule out the backup lights as the problem, the first thing is to try to isolate the problem to either the front or rear of the car. Instead of using up fuses I would make up a 15 amp circuit breaker and put it in where the fuse goes but that's up to you. A volt ohm meter/ multimeter will also help, start at the rear and check for short to ground, disconnect the battery, turn switch on, remove the bulbs at the rear and start checking for a short to ground on each bulb socket contact, I believe the tail light wires are solid green, if a wire is shorted you are closer to finding the problem, remove the front park light and side marker bulbs and see if the short is still there, it's just a matter of finding the wire that is grounded. If you find a shorted wire disconnect the combination switch, the connector is under the steering column, if the short disappears the problem is the switch. Let me know what you come up with so far.