Cluster lights and Headlight not working

The XJ Gods decided to curse me once more after chasing a carb issure for 3 years on my Seca 900. Headlight and cluster lights stopped working just like that. Leading up to this my signal lights, brake lights, tach, and horn stopped working which I was able to trace back to a poor connection at the fuse box. They work fine now. I installed a blade style box two weeks ago, but it seems this time the fuse box is fine. I checked the bulb in the headlight by directly connecting it to the battery and that worked fine. I checked for continuity from the fuse box to the headlight with my multimeter and sure enough there's continuity. I also checked for voltage at the fuse box and I'm getting that as well. I even checked for voltage at the headlight harness and I get voltage when I turn the ignition on and off. Keep in mind I tried these tests turning the bike on as well because I know that with certain old Yamahas the bike has to be turned on in order for the headlight to work. I also checked to make sure the bike was charging and I get 14.5 volts at the battery when the bike is on. There's no obvious reason why I'm having this issue. It might be important to mention that I replaced all the main bulbs in the cluster with LED's. It's been working fine like that for a year and a half with no issues. Anybody have any suggestions.

 

Looks like the 900 uses the combo starter / headlight switch. So the common here between the instrument backlights and headlight is the starter switch. The fact that the instrument backlights and headlight are not working is pretty good proof the combo switch is not working.

This could be if you checked it under no load condition

It would be best to backprobe the headlight H4 connector with the headlight hooked up and the key set to ON, and do the high and low beam while switching the left control to the appropriate test. You should get battery voltage at these two wires - Y when switched to high beam, and G when switched to low beam.

If you get 12V backprobe the black wire on the H4 connector to verify you have a good ground. It should read zero volts.

 

Soooo, it turns out that if I unhook the main harness to the headlight then the instrument back lights turn back on!

One thing I failed to mention is that I was changing the fork oil and made a bit of a mistake by forgetting to prop up the front of the bike before taking the fork top bolts off. The front of the bike nose dived after taking off the second top bolt and I'm wondering if something came apart. Just thought I'd mention that.

 

So I conducted this test and I am getting some weird readings. I get 50 volts on ALL THREE terminals on the H4 connector, this includes the ground, when the ignition is turned to ON and it doesn't matter if the high beam is on or off. When I turn the ignition off I get no readings whatsoever. Like I mentioned before the instrument back lights turn on when the headlight is disconnected. Something is weird.

 

Bad voltmeter, if it is actually reading 50 VDC........

Flickering lights typically means a loose connection somewhere, either hot or ground.

 

I think if you look closely you will see the meter is diplaying 50 mV

Quite normal if you have a load upstream as the current from the headlight is huge compared to the backlights, especially since you added LED.

And the flickering, pretty common with LED's when they are starved for voltage

So, everything still points to the combo starter / headlight switch, or perhaps since you mentioned dropping the forks the right control connector is not fully mated or wiring is damaged and causing a poor connection, but just guessing not as likely as the starter switch as the right control connector also has the kill switch wiring

 

Thanks Rooster. When you say combo starter /headlight switch are you referring to the ignition key switch? Little confused.

 

Rooster. Has anybody said you’re good. Like, REALLY GOOD. Sure enough I pulled apart the harness to the rh starter button/kill switch which you referred to as the combo starter/headlight switch and simply put back together and the headlight turned right on. Im guessing that the nose dive of the bike when pulling/undoing the fork top bolts revealed a loose or corroded connection. It’s funny because I went through ALL the electrical connections in this bike and cleaned them up as best I could and then I put dilectric grease on them. However, I have read that it’s not good to put dilectric grease directly on the connections themselves but rather to SURROUND the connection with the stuff. In any case all systems are go and I thank you once again!

 

Good that it is working, but from the sound of that the starter / headlight switch might need some attention. When you push the starter switch it breaks the contacts on the headlight switch, when released those contacts close again and the headlight illuminates. Those contacts can get dirty, or there might be some mechanical issue there not allowing the contacts to close hard enough. So, a good cleaning may be in order for the contacts and mechanical mechanism

 

Got it. I'll give it a thorough cleaning. Thanks.

 

I’m so glad I found this. I got my first bike when I was 19 and it’s a very good looking 1982 xj750 maxim. I unfortunately have the same problem with the headlight/ tachometer lights and the aux light not working from time to time. My temporary fix when that happens is to pull out the starter button in a wiggling motion and the lights on the dash and and the headlights come back on, but now even when I do my said temp. Fix now nothing seems to work. I took apart the hi-lo switch first because I was reading that it could just need a good clean but I’m astounded my brain never thought of cleaning up the connections on the starter button and the killswitch. I will be doing this after work today with the knowledge I have acquired. Thank you guys or gals for asking all the questions before me!