when i have it all the way just the side markers are on. when i have the switch halfway sometimes just the beams come on w/ no markers. i have to get the switch in the middle of turning both on. i replaced the female end and new hl switch but i eventually had the same problem
From your description, the switch sounds bad. I know that you replaced it, but with what? a used part or new part?
If it was a new part, I would clean all connections going to that switch, make sure to use dielectric grease when reinstalling. If that doesn't clear it up, I honestly think that you should investigate the computer... I don't know about headlights, but when I removed my alarm system from my mustang, the blinkers didn't work. When I put it all back together, the car would start with no blinkers however. I changed the computer due to starting issues (after some time), and ther frickn' blinkers started working again. I was surprised how many things are controlled by the computer in this car.
But it really sounds like you just have a bad connection. I would firtst try looking at the connections going to the lights and the connections going to the switch.
I can assure you that the computer on a 5.0 Mustang is not connected to the lights in any way. The only thing they have in common is that they both use electricity to operate.
when i have it all the way just the side markers are on. when i have the switch halfway sometimes just the beams come on w/ no markers. i have to get the switch in the middle of turning both on. i replaced the female end and new hl switch but i eventually had the same problem
EDIT: I misread the initial post so disregard the following.
Unless your high beams were selected, there's another issue afoot anyhow. The headlight switch only sends raw power - it does not control low or high beam switching.
The MF switch receives power from the hdlt switch and divvies it up depending upon your switch selection. You can have highs and lows come on (with no marker lights) during FTP but the power source for this function isn't even the headlight switch.
Because of the other issue at hand, I would check over the MF switch, its wiring connections (known for backing out of the connector shell) and the wiring (burning up on occasion). The headlight switch might still be an issue but since there are a couple of things going on, I would want to examine both sets of switches and connectors.