Headlight Not Working

[DamnHeathen]

I am having a problem with my headlight...it not working...fuse is good...filament is good...could it be the headlight unit or the reserve? Need input.

[motoman]

I am having a problem with my headlight...it not working...fuse is good...filament is good...could it be the headlight unit or the reserve? Need input.

Most likely the conglomeration of plug-ins of wiring inside the headlight bucket housing. The plug-ins stored inside that housing are notorious for getting corroded from exposure to elements.

[ViperRon]

More than likely is what Moto said but you can jumper across the headlight relay and see if that turns light on. If that does one input comes threw a diode hidden in the wire harness to the relay to turn it on. It is not a solid voltage going to the relay what happens is voltage comes straight from the alternator Ac gets to the diode and you have a pulsed Dc coming out from diode to relay. When the signal is constant enough it triggers a self hold path for the head light. It was done this way so that in starting the headlight would not draw power from battery.

[bikerphil]

To bypass the headlight relay, unplug it, and in the harness plug, jump the red/yel and the blu/blk wires and the headlight should come on with the key in the on position. The relay is located under the fuel tank towards the front, near the ignition coils.

[TopCatGr58]

What has not been stated is that the headlight relay is triggered once the bike is running and the ALT is creating/generating a charging current. IS your tachometer working when the engine is running, the tach is also fed/triggered by the ALT, but if the ALT isn't working right, then both the headlight won't come on and the tach won't display the rpm.

Bypassing the relay will tell you if the headlight will work, but doesn't tell you WHY it's not.
As mentioned, the wire from the ALT goes thru a diode, it can burn up and stop working and then you don't get pulsed DC to the relay. OR the ALT isn't working so it's not sending the AC signal to begin with, could be shorted windings of the ALT, or the Reg/Rect is damaged, etc.!

T.C.

[Orange4]

Opposite problem

I have the opposite problem. My headlight relay is now always energized. Drained my battery. Headlights remain off until ignition on though. Have not checked charging with a volt meter but it seems to work.

How does the charging system trigger the headlight relay?

[DamnHeathen]

toggle switch

I will bypassing the relay...I did a quick fix for now...hotwired the headlight to the battery with a toggle switch.

[TopCatGr58]

I have the opposite problem. My headlight relay is now always energized. Drained my battery. Headlights remain off until ignition on though. Have not checked charging with a volt meter but it seems to work.

How does the charging system trigger the headlight relay?

I sorta explained it in my reply above yours, but there is a white wire that is a TAP off of one of the 3 phase/circuits of the ALT, it then runs to a DIODE in the harness that converts the AC power into Pulsed DC power that throws the headlight relay....it's a latching relay that stays thrown once the pulsed DC power gets to it, but once the bike is turned off, it's supposed to release the latch. I bypassed my diode a while back after first trying to fix/replace it but the headlight relay still wouldn't work. I then rigged a remote toggle switch to throw the headlight relay using just regular 12V DC, but throw the toggle switch OFF once the headlight relay is latched. However, that toggle switch has gotten thrown by accident with the bike off, so I couldn't tell that the headlight relay had been energized, and it ALSO drained my battery!

SO...if yours is staying latched, either the relay is bad, or you have some wires crossed so that you're getting DC power into that white trigger wire somehow....but my bet is on the relay being bad!

T.C.

[DamnHeathen]

I installed a push/pull switch which is helpful on accidental headlight on when bike is down.

[bikerphil]

Just to clarify some, the 78-79 bikes use a different relay than the 80-81's.

The 78-79 relay is triggered by the yellow wire coming from the alternator and there is no harness diode as in the 80-81 bikes.

[Orange4]

It was probably the rectifier. I swapped it with my 79 erstwhile parts bike and it works now.

Guess I need a new rectifier for when I finally get the 79 going.