The Hayes book - as often as we give it bad reviews here - has a decent wiring diagram of the '86 forward headlight wiring system. It's mislabeled as '85 forward or something in my edition, but of the two that they show for headlights, it's the later one. It's the one showing two relays.

I'm sure the Bentley's book has more/better diagrams of the same.

The usual suspect in headlight problems is the main headlight relay. Details below.

Wiring system is essentially this:

Dash switch is powered only when key is at position II or III.
Dash switch sends 'signal' current to the headlight relay located on driver's kick panel. Half way up, left side. Sometimes comes off clip and falls to bottom. Small silver-colored cube about 1 inch on each side. Nothing else in the area looks similar. Has two fat wires and several thinner ones, and a white connector.

This headlight relay is a known failure item. It can get very hot which tends to damage its connector, and also is not good for the relay. You definitely should have a look and consider replacing the connector and/or relay.

Headlight relay (above) receives battery power from fuse panel always (NOT fused, either). This power is sent forward to the headlights when the dash switch is "ON", which activats a coil in the relay. When the coil is activated the relay closes its internal contacts which sends the power from the fuse panel up forward to the engine bay.

The relay contacts open again (to stop sending voltage to engine bay) when you turn the dash switch off. Turning off the ignition also opens the contacts as there's no voltage at the switch for it to send down to the relay.

In the engine bay the voltage goes to the step relay. Step relay is controlled by the high beam/low beam switch on turn signal stalk. Step relay sends power from the main headlight relay either to the low beams or high beams. Low beam power goes through Bulb Failure Warning Relay (BFWR) first before going to bulbs. High beam power does not go throufh BFWR, goes directly to the bulbs.

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DAMHIK: Don't Ask Me How I Know - - - Sven: '89 245, IPD sways, electric rad. fan conversion, e-codes, 28+ mpg - auto tranny. 500 mi/week commute. '89 245 #2 (wifemobile). '90 244 (spare, runs).