I was driving my truck tonight and noticed Fog lights were out. I checked the fuse and it was blown, replaced it three times and everytime I turned them on it blew. Could this be the relay switch causeing this or a bad bulb. I have not done anything to the vehicle as far as the wiring goes, Thank You.

 

If the fuse is blowing it is apparent that the circuit is drawing too much current. This is more likely caused by a short in the wiring (a cross between the positive (hot side) of the wiring to the negative side (frame of the truck). This would be fairly easy to verify if you were competent using a volt-ohm meter, but If you are not, it may require professional service.

I would try examining the wiring harness that connects to the lights, looking at it as far as you could trace it, to see if there is any visible damage to be seen. It would be a rare thing indeed if a bulb was causing this problem, but a defective socket could possible cause it, but then, there are other components that could also be causing this over-current problem. You might try removing both of the bulbs and then turn the lights on and check if the fuse still blows.

To answer your original question, yes there is an outside chance the control relay could be defective. Here again, you could check this relay with a VOM, but other than that, a direct replacement would be your only choice. Without checking, I'm not sure of one of the other relays in the box is identical to the fog control relay, but if it was, you could try substituting another relay temporarily to check it. In situations such as this where there are several possibilities, I have simply given you the most obvious ones first, if you have anymore questions, post again.