2005 4.2l stx low beams not working. New fuses new switch and new signal switch new battery. Still not working

 

Have you checked the relay?

FWIW, you can test relays with a 9v battery and a meter really quick on the bench.

 

I checked the relay for the high beam. Do not know where the low beam relay is located.

 

There is no relay to check in the low beam circuit.

It's a straight circuit from fuse F40, through the headlight switch, through the MFS, through individual fuses for each low beam circuit and then out to the low beam bulbs. Nuthin' fancy.

 

I think I would check the power at the bulbs. It might be as simple as burned out bulb filaments.
I replaced my headlight bulb in my 2007 Yamaha Venture motorcycle which uses a 9003/H4 bulb with a Sylvania Ultra the brightest one. It burned out immediately on both filaments??? So, I bought the lowest output bulb and it works great.