KoupEsEcks -
You're going to turn on the engine, turn on the fogs and then probe the end of the connector that plugs into the fog light bulb with either a DC voltmeter or a DC volt-detector tool (a lightbulb inside a screwdriver handle with an attached ground wire). Obviously, you should have 12 VDC (or about 13.8 VDC if the engine is running) going to one pin of the connector. If you do, you then have to check the OTHER pin inside the connector and see if you still have GROUND. This is best done with a voltmeter set to the lowest "Ohms" setting, or some of the voltmeters have an audible "continuity check" that beeps if a connection is good.
Just doing the DRL mod (as I have done) should not have compromised your factory wiring harness in any manner. I suggest for peace of mind to go and visit Harbor Freight Tools and pick up one of their VERY inexpensive multi-meters
Digital Multimeter - Save on this 7 Function Digital Multimeter when on sale, sometimes you can pick one up for $1.99!!!! That's throw-away pricing.... if it breaks, or you drop it, or someone steps on it, who cares!!
Anyhow.... my two cents.... see if that helps you figure out what's wrong.