A standard SPDT relay will work, I recommend BOSCH for all relay needs.
I would wire it so that terminal #30 goes TO the fog light bulbs. Terminal #87a will connect to the ORIGINAL wire from the light switch that operates the fog light normally. Wiring it this way, you will have "normal" fog light operation if the relay is not energized. So if the relay goes out, you still have the normal operation as a backup.
Terminal #87 will be the power terminal. This is the fused circuit from the positive battery post or other positive power point. I don't know what wattage bulbs you are using, but I would run a line directly from the battery positive post.
Terminal #85 and #86 will be for the trigger circuit. You can wire this portion up a number of different ways. You can tap the #87 for the power into #86 and then just ground #85 via a switch to turn on the lights.
But since you want the fog lights to operate like DRL and automatically come on with the ignition switch, I would find a circuit that gets power when the ignition is on and tap into that to energize the relay. Terminal #86 will be connected to this power and #85 will be grounded.
So when you turn on the ignition, #86 is energized and completes the circuit via #85. This triggers the relay and opens the #87a to #30 circuit and connects #87 to #30.... voila! your lights are on.
When the ignition is turned off, the magnetic field collapses and #87a and #30 are reconnected.
Hope this helps!
Last edited by dsantos; 09-24-2001 at 05:19 PM.