Headlight stopped working

1987 XJ900 F. Headlight suddenly stopped working. Battery fine, different globe tried, fuse box OK, Light switch opened and tested fine. Tail light working OK. The odd thing is that I have 12 volts at the 3 headlight plug terminals yet globe does not work! This has me stumped! I note on the schematic there is a cut out relay. Does this cut the headlight when the starter is deployed? Where is this relay located pls? Interestingly the other day when riding a red light came on. this usually happens if somebody presses the starter when the motor is running. At the time I determined that the starter switch was sticking. I sprayed it with contact cleaner and thought that was the end of the matter - red dash light didn’t come on. Now I’m wondering if the two incidents are connected! Suggestions welcome .

 

Headlight relay:

This relay prevents the headlight from coming on while the starter motor is being engaged, thus allowing maximum battery voltage to be used by the starter and the ignition system. However, it is dependent on voltage draw in order to energize and "latch" into the on position, and thus if the engine gets spinning fast enough during the starting process (whether the engine fires or not), enough voltage will be produced by the alternator (which increases its output with RPM's) to clamp this relay, and thus pass current to the headlamp. Also, once latched on, the headlight circuit remains on until the ignition switch is turned fully off.....thus, if you (for example) stall the bike, and hit the starter button, this relay will remain latched and the headlight WILL remain lit during the starting process. Only by turning the key to the off position can you de-energize this relay (and thus turn the headlight off).

- due to many variations in design and the need for visual reference, you should check your service manual for the proper testing procedures. There are at least three checks that are necessary to perform: a relay coil resistance check, and a relay coil function (powered vs. unpowered) check, and a diode function test. Here's what it looks like inside:



For an on-bike test, you can:
- disconnect the White with blue tracer stripe wire at the headlight relay.
- turn on the ignition - the headlight should be off.
- momentarily jumper 12V to the pin on the relay where the white/blue wire was connected, and the headlight should come on and stay on.


For North American models, here is the info, don't know if it's the same for a 1987 XJ900 model:

OEM main HEADLIGHT RELAY 3H5-81950-00-00
inked 3H5-00 on top of metal cover
note: latching relay
Tab Color: yellow

TESTING:
- will need a short jumper wire
- will need a charged 12V battery
- attach testing harness to relay, note that it only fits one way!
- test the following:

WITHOUT BATTERY HOOKED UP:
Green wire to white wire: 100 ohms

WITH BATTERY HOOKED UP:
- measure the current voltage of the battery being used for testing and record it for further reference below.
- attach positive (+) battery lead to Orange wire
- attach negative (-) battery lead to Green wire
- use a jumper wire to temporarily jumper the Orange wire to the White wire. NOTE: you should hear a click, then remove the jumper wire. If not, relay is bad.
- measure the voltage at the Black wire vs. battery ground, it should be = whatever the battery being used voltage is at. IF SIGNIFICANTLY LOWER, then relay is bad.
- remove the battery + from the Orange wire.
- hook up battery + to the Orange wire again.
- measure the voltage at the Black wire vs. battery ground, it should be = 0. IF THERE IS VOLTAGE, then the relay is bad.

 

Len, thanks so much for your helpful reply. Having located the offending relay, I cleaned up the terminal/plug, turned it on and bingo, headlight working!

 

Hello All

I have an XJ750E-11 which most of you probably know is a Japanese market (only) bike. It is a 1983 model. I have recently restored this bike and almost everything now works except the headlight. The pilot light works fine, and headlight works with the pass switch, but not with the switch on the right hand switchgear. I have checked the relevant switchgear block connectors and disassembled the right hand switch and everything looks fine. I wonder if what I think is the headlight relay - which is part number 29R 83396 00 on my bike - is defective? It has blue/white, brown/white, black and blue wires and is connected to a block connector in the headlight shell which is a cavity in the fairing. The blue wire in that block connector goes to a double female connector with apparently no male counterparts to insert. I have checked function with the engine running and it still does not work. Very grateful for any ideas! Best regards, Stephan

 

The Haynes has the UK XJ wiring diagram and it does not have a headlight relay. It is also not a good diagram as it has errors in the lighting circuit. Perhaps you have a diagram you can share?
My guess is the headlight flash switch is bypassing other switches and that is why it works. I would take another look at the lighting on / off switch and the dim switch to sure they are working and no wires are broken.