If you checked the switch, fuse and bulbs the only thing it could be is a open ground. Find the ground wire on the bulb socket and check for continuity. With a tester put one wire one the ground at the socket and the other on the neg. battery terminal
faulty switch
Stop the car in a safe place at night. Put the car into neutral and apply the handbrake. Switch on the headlights. Get out of the car and look to see that the headlights are working.
The headlights on a Jaguar my not work if the bulb or fuse is defective. Alternatively the wiring can be damaged or the switch my have stopped working.
in 1986 the headlights weren't fused the likely suspect would be the dimmer switch if it was located on the floor.
To find the cause of the low beams not working, start with the bulb to make sure both are ok. Check the dimmer switch, and the wiring from the switch to the headlights.
heck the fuse first, then the switch.
i would have the light switch checked to see if it is faulty
Yes it could.
I just had the same problem in my '97 Nissan pickup. Both headlights stopped working at the same time. I went through some hoops, including trying a new headlight switch, but it turned out to be some corrosion in the plug for the fusible link that bolts onto the positive terminal of the battery. I cleaned that out and it is working fine again.
You didn't mention if you checked/tested the low beam headlamps or not.
It is probably the running lights that are working and the regular headlights aren't working because of the switch or wiring. TAke it to a garage.
The circuit is simple .... headlamp bulbs to relay to fuses to switch .... ttroubleshoot those items and you'll find the glitch