When i turn the headlights on the time on the clock dims

There. May be a problem with the fused , check all the fused .

Have you tried to replace the headlight switch? I ask that because you say the radio and clock go out, with the headlights on clock and radio go dim, so not so bright at night but bright in day to see them. So maybe the switch is bad?

turn up the dimmer switch. sound like its down at low setting.

clock light always dims when park or head lights turned on

Is this for a 1999 Forester or for a 2004 forester, the title lists both years. If it is a 1999 model then the problem most likely resides within the clock itself. Unfortunately, many clocks of this vintage go bad over time. I offer a reasonable repair service and many clock removal instruction sheets at www.autoclockrepair.com
I'd be happy to assist.

they should dim unless they are unreadable check the dimmer control at the headlight switch

if your running trailor lights and have a plug hangen back there make sure the connections arnt shorting against each other that coul cause the prob

Pull the headlight switch and check for a burned connector, this will cause a poor connection and in turn dim headlights or no lights.

Does it go completely black or just dim? Most displays dim when you turn the lights on to make the display darker so its not too bright. GPS and other displays do this. Do you have any problems with any other of the car's electronics?

There is a dimmer module that dims all dash lights when the headlights are on.