One headlight works then shuts off when beams are on

If he is getting voltage when he turns the headlight switch on at the socket and the ground is good. The bulb is bad period.

Circuit is grounded via the light sensor.
Light switch is the multifunction switch that yuou turn the lights on.

Btw are the lights flipping open and remains open when lights failed?

When there is no voltage, grounding would not work.

My previous post had the following mistakes:

Lowbeams
Red/Yellow (right side)
Red/Blue

Highbeams
Orange (right side)
Orange/White.

It should be thus.

High beams
Red/Yellow (right side)
Red/Blue

Low beams
Orange (right side)
Orange/White.

You have 2 problems here.

1. Faulty light switch or its wiring between light switch to the headlight bulbs. The high beam circuit is not transferring the required voltage to the headlights.

2. Faulty light sensor or its wiring/ground circuit.

At left headlight, with lights turn on to low beam, ground the Pink/Black wire and if headlight turns on, you would need to repeat test at light sensor for same wire to see if the light turns on.

At light switch test the Red/Yellow and Red/Blue wire for battery voltage with high beams turned on. If you do not get battery voltage, the switch is bad.

2.

Refer to the diagram I posted earlier.

Do you have cruise control or intermintant wipers?Which ones do you have?

I see it coming as both levers they have them on Www. Rockauto. Com and amazon.

There expensive I would look at pick a part or ebay.

Good luck let me know what you find.

If you want to give it a try, remove the back cover of the light switch and check the contacts. You might be able to repair it

U could allways call some salvage yards to locate 1

At this age, salvage yards are a long shot.

They have a locater that checks if the part is anywhere in the usa. Have u checked that voltage is at the dimmer switch for voltage and when u turn on the high beams on the voltage is being sent on the wire. Because the head lights go from switch to dimmer switch then to head lights. Hope this helps.I think the switch is a shot in thedark.U need to check your voltages first. Gl