I suggest your ground to the frame, if this is broke, rusted, or loose....there is your source. After all the factors you have described and checked my arrows point to a sure ground. I hope this helps!! Write us back if you need further assistance!!
So far, so good. Sounds like you have checked the obvious. When you replaced the bulbs, switch and fuse, were they bad?
Before you go totally crazy, double check the parts you put in to make sure the parts are not defective. Also, check the charging system. Sometimes an overcharging alternator will blow lights. (should be 13.6-14.3 volts).
〉 Answered on Apr 1st, 2011 by Audra Fordin, Owner at Great Bear Auto Shop
When you say you checked the wiring, did that mean you put a meter on it to see if there's power when you turn on the lights? If you have power at the light socket the bulbs should work. If not you need to trace the wires back until you find the point where there is no power.
This means probing the wire. Sometimes problem wires cannot be seen with just the eye. You need to use the meter at all areas of the circuit to find this problem. Good luck.
〉 Answered on Apr 1st, 2011 by Lori Johnson, Owner and Instructor at Ladies Start Your Engines
One thing you did not mention - do you have a good ground? If you do, I would start at the bulbs and work back. If you have power and a good ground at the bulbs - the bulbs are bad etc. Make sure you have a good test light and multimeter so that you can be sure your readings are accurate. You may have to actually ohm out the wires to make sure there are no breaks.
〉 Answered on Apr 1st, 2011 by Suzanne Grego, Technician at City of Philadelphia Fleet Management