Head lamp wont work

wow very old van.
so engine runs car drives ok , right, just head lamp problems.
HL flasher work or not, (hi beam flash switch)??????
in HIGH beam mode is cluster hi lamp glowing?
no? fuse is blown.
well a volt meter finds the cause most easiest.
and schematic from the service manual.
telling what engine or VIN first, is best
or the wrong fuse boxes are seen,, ok>?
you checked fuse but forgot this van has lots of fuesible links. like this super simple schematic shows.
nothing can be more simple, no BCM computer mess.
it can only be 5things (engine runs)

1. fuse link
2. dimmer
3. HL switch
4. both lamps burned out, nah
5. grounds to both lamps cut/rusty.

if both lamps lugs are at 12vdc, the ground is dead

I would check the fuses first. Headlights are typically on a separate fuse then the parking lights. If the fuse is fine check and see if the Bulb is burnt out but it is rare for both lights to go out at the same time.

Are both low beams an high beams not working ? What engine does your car have ? Low beam relay only on 2.2 L .
On vehicles with manual headlamps, the LH HDLP and RH HDLP fuse in the fuse block - under hood, supply battery positive voltage to both low beam lamps and high beam lamps at all times. The low beam and high beam circuits continue through the fuse block - under hood, through the body control module (BCM), and to the headlamp switch. The low beam or high beam circuit then, depending on the position of the dimmer switch, continues through the headlamp switch. When the headlamp switch is placed in the ON position, it provides a ground path for the low beam or high beam lamps through G203. The low beam and high beam circuits are monitored by the BCM.
Is there B+ voltage at the headlamp fuse's ? Power runs from fuse through the head lamps to the dimmer switch through the head lamp switch to ground when turned on . If there is B+ voltage at the fuse ,check for voltage at the headlamp switch .
The

Make sure the other filament is good and that it is receiving power. If no power check relays, fuses, switches,etc for low beams.

There are several reasons why your headlamps an running lights don't work , the headlamp switch is a good one ,plus relays an the DIM - dash integrated module an associated wiring ! Here is how the headlamps work , right out of Buick factory service info !
The dash integration module (DIM) provides battery positive voltage to the signal circuits of the headlamp switch. The signal circuits include the headlamp switch headlamps on signal, the flash to pass switch signal and the high beam input. With the headlamp switch in the ON position, a ground path is available for the headlamp switch headlamps on signal circuit of the DIM through the headlamp switch. The DIM provides ground to either the headlamps high beam relay control circuit or the headlamps low beam relay control circuit of the low beam circuit. The position of the headlamp dimmer switch determines which relay control circuit has ground. The DIM supplies battery positive voltage to the relay control circuits, if the headlamps are necessary. The fuse block - underhood supplies battery positive voltage to both relay switch circuits. When the low beam relay control circuit is energized, current flow is to both low beam fuses and to the low beam headlamps. The headlamps have ground at G103 and at G401. When the headlamp high beam relay control circuit is energized, current flow is to both high beam fuses and to the high beam headlamps. The high beam circuit is divided into a left and right side circuit. The current flow of the left high beam is from the fuse to the left high beam lamp. From the lamp, the current flows to the normally-closed contact of the DRL relay to G103. The current flow of the right high beam is from the fuse to the right high beam lamp. From the lamp, the current flow is to ground at G401. When the headlamp dimmer switch lever is pulled toward the driver, the flash-to-pass switch closes. This grounds the DIM flash to pass switch signal circuit. In response to this input, the DIM energizes the HDLP HI BM relay. Both high beams remain on until the driver releases the switch handle. If the low beam headlamps were on during a flash to pass operation, the low beams remain on. The headlights may be switched to high beam with the opposite movement of the headlamp dimmer switch lever.
By running lights , do you mean park lamps or day time running lamps ?
Park, Tail, License and Marker Lamps
The park lamps, including the license lamps, are turned on when the headlamp switch is placed in the PARK or ON position or anytime the headlights are requested. The fuse block - rear supplies battery positive voltage to the switch contacts of the Park LP relay. When the headlamp switch is in PARK or in ON, the park lamp switch on signal circuit of the DIM has a ground path. The DIM provides battery positive voltage to the control circuit of the Park LP relay. When the park lamps and/or the tail lamps are ON, the DIM energizes the park lamp relay control circuit. This closes the switch contacts. Current flows from the Park LP relay to the LH PARK LP and the RH PARK LP fuses. From the fuse, the current flows to the park lamps. The left park lamps are grounded at G103, G401 and G402. The right park lamps and the right tail lamps are grounded at G103 and G401. The DIMR fuse supplies battery positive voltage to the license lamps and to the DIM instrument panel lamp fuse supply voltage - 1 circuit, for interior lamps dimming. The license lamps are grounded at G401.
The best advice I can give is that you take this to a ASE certified professional repair facility unless your a qualified automotive electric repair person !
Diagnostic Starting Point - Lighting Systems
Begin the system diagnosis with the Diagnostic System Check - Lighting Systems . The Diagnostic System Check will provide the following information:
?€¢
The identification of the control modules which command the system

?€¢
The ability of the control modules to communicate through the serial data circuit

?€¢
The identification of any stored diagnostic trouble codes (DTCs) and their status

The use of the Diagnostic System Check will identify the correct procedure for diagnosing the system and where the procedure is located.

The

I suspect it is the headlight switch

Well the high and low beam lamps use the same fuses, and the dimmer switch handles the ground circuit. So I would check the dimmer switch if both high beam bulbs are ok.

You have a electrical issue in the combination switch.

There is a relay and a fuse you need to check in your hood compartment fuse box. Check under parking lights, head lamps L & R Low Beam and Head Lamps L & R high beam. You will definitely have one blown. Its a cheap fix so get her done. Good luck.

You headlight lamp have a diffuser mechanism which allows it to flip between the hight beam and low beam feature of the bulb. In fact, you high beam will function even if the low beam is not working.

I would recommend the purchase of the new headlight lamp. It would cost you you any where from $15.00 per unit to get a replacement lamp