hibeams not working at night

[68bullit]

first post here kids and could use some help.i have a 99 yukon denali and has the daytime running lights(canadian model)

 

ok heres the dealio-during the day my head lights work fine as do the hi beams but as soon as it gets dark my lights go to the low beams and hibeams dont work while vehicle is running.

 

if its shut off and turn the lights on manual day or night they r fine but again when running notta.

 

can someone shed some light on this?had one guy say maybe the twilight sensor in the dash another say the hi/low beam indicator arm stuck between both spots and of course the only part left the actual headlight switch.

 

i do all my own work and drive older trucks so never encountered this before on mine or any others ive repaired.

 

thanks for any replys

[mmmikkke]

Are your fog lights off? Some GM trucks in the past would not permit high beams if the fog lights were switched on.

[GM-Tech]

Some GM trucks in the past would not permit high beams if the fog lights were switched on.

 

<{POST_SNAPBACK}>

 

 

 

It's actually just the opposite. If the high beams are on, the fog lights will not turn on. OE fog lights will only come on with low beams or parking lights. Turning on the fog lights in no way disables any of the headlights.

[GM-Tech]

ok heres the dealio-during the day my head lights work fine as do the hi beams but as soon as it gets dark my lights go to the low beams and hibeams dont work while vehicle is running.

 

This is rather oddball problem for which I have few answers. I think you can forget about the light sensor being the problem. Since things change from day to night, the sensor is apparently able to detect light/dark.

 

How that ties in to just the high beams not working is beyond me. If the lights work properly with them switched on manually, then that should eliminate the dimmer switch. It doesn't know what mode the headlights are in.

 

If I had to guess, I'd say a daytime running light module, but that's just a wild guess. This one would need some extensive diagnosis to determine what the heck is going on.

[68bullit]

ok the headlights function regular(hi beam/lowbeam/fog lights)during the day but when it gets dark the lows are fine the fogs are fine just no hi beam function.

 

if the truck ignition is off at night everything functions fine but when you turn the ignition on whammo no hi beams.

 

1 other thing the dr side heater in the seat cushion doesnt work which fuse would operate that seat and the 3 other seat function fine