What would be stopping me from powering the fog lights I bought off ebay from the power side and ground side of the low beam headlights?

Besides perhaps drawing to much power and blowing a fuse (the lights are H4) is their anything stopping me from doing this? This would save me the trouble of wiring a fog light switch and relay system and would be pretty straight forward to do.
Just wondering thanks!

 

It will take only a little longer to wire up the lights the correct way the first time. If you butcher it, chances are you will only be back to fix it the right way later.

 

Stock wiring isn't sufficient guage for the stock headlights - it surely won't run fogs too without melting.

Do this right - it's easy:

Pos wire from fuse box to fog light switch - any small wire will do
Ground to anywhere if switch is lighted - any small wire again.
Pos wire from switch to relay underhood - any small wire again
Pos wire from fusible link center to relay - nice guage here (larger)
Ground wire from relay to anywhere
Pos wire to lights - nice (larger guage) wire here.
Grounds from each light to anywhere.
Done.

This will work even with the factory foglight switch which you can find on ebay. This is how I did mine with factory switch in my RS that had no fogs.