Help please, my headlight quit.

[fredintoon]

Hi List,
I just resurrected my Flying Pumpkin XS11SG/SofA sidecar rig after 3 years gathering dust in the back of the garage.
Fired up on 2 out of 4 after a carb clean.
Fired up on all 4 after the 3rd clean and replacement float needles & seats and slow running needles on all 4.
Bought the bike a prestige plate that sez XS11 to replace the one that sez XS.
Took a tour down town.
Finally noticed that the headlight wasn't working.
WTF? It worked when I parked the bike back in 2014, eh?
Everything electrical except the headlight works as it should.
Both bulb filaments light up when connected to a battery.
Multi-meter's 200 Ohm setting shows continuity as best as I can tell through the Hi/Lo etc. handlebar mounted control switch and it's harness.
So what next, folks?
I forget if the headlight should come on with the ignition or if it needs to have the engine running like an XS650?
Does the headlight have it's own fuse or does it share one?
Is the headlight connected via a mystery module and if so what's it called, where is it located and can it be bypassed?
If I must, I can bypass the entire problem with generic bar-mounted switches and an in-line fuse but that's only as a last resort.
Thanks in advance for any suggestions.

[bikerphil]

Hi Fred,
The headlight has it's own 10A fuse.

The relay can go bad, it has 4 wires it is located under the tank towards the front near the ignition coils, A jumper wire between the red/yel and the blu/blk will bypass it and the headlight should come on with the key on, engine needn't be running.

[TopCatGr58]

Hey Fred,

Well, since you made it to town and back and the bike didn' t die, then your charging system is probably working okay, but that's another reason why the headlight wouldn't come on. Did your tach work correctly? Throw a voltmeter across your battery poles and fire it up and rev it up to 2500 and make sure you're getting your 14.5 volts, if still 12 or less, then the charging system has developed a problem.

Along with the Tach, it sends a power signal to the relay to throw it once the engine gets running and produces a charging voltage....but if not charging, then no power signal to the relay and no headlight.

Along these lines, there is also a DIODE in line, and they can also go bad and prevent the power signal from getting to the relay.

I bypassed my DIODE, but kept the relay, and like you said, installed some handlebar switches so I could still keep the headlight OFF while starting, and then throw the switch to latch the relay....but the switch is a temporary one, in other words, it just sends a quick power signal to latch the relay, but then stops sending the power, it's not needed once the headlight relay latches and turns the headlight on. And of course the relay releases when the key is turned off.

T.C.

[fredintoon]

Hi Bikerphil, TopCat,
thanks for the prompt replies.
Yes, the tach works. The only thing that don't work is the headlight.
Phil, the headlight fuse has to be one of the three that are gang-fed from a tan wire?
Sure, check 'em all but if the fuse is OK what color is it's output wire if I need to look for a broken one?
TC, I'd forgotten about that hidden diode. If the thing can be bypassed, why is it there anyway?
I'll try the relay bypass first as it's the easiest to get at. Jumper Red/yellow & Blue/Black but what about the
Black and white wires, just leave them open?

[skids]

Fred, I have used a solenoid switch for the headlight for years. You can get an off/on switch for the bars on the left grip area to operate the solenoid on the low current wires. The advantages are that you can switch on/off the headlight, and the circuit is simpler. The disadvantage is that you lose the reserve lighting function. But, that said, if the high or low beam burns out, just switch to the opposite beam. The 78's came with an on/off switch but it locks on once the engine starts turning. You would replace the stock locking solenoid with the new one.

[skids]

I am sorry, I should have said "relay switch" instead of "solenoid" as I think that is what it is called.

[bikerphil]

Fred, it would be a red/yel wire at the 10A fuse.

No need to do anything with the black and the white wires at the relay connector, just leave them alone when bypassing.

[fredintoon]

I am sorry, I should have said "relay switch" instead of "solenoid" as I think that is what it is called.

Hi skids,
whatever the thing is called, and I've no idea what goes on inside it to switch away from a dead headlamp bulb filament, mine didn't work no more.
Of all the things that could have interrupted the headlight's power supply
(and thanks to those who pointed them all out) it was the "usual suspect" after all.
Bridging the Red/Yellow and Blue/Black contacts in the relay's wiring socket let the headlight come on with the ignition switch once more.
I'm not concerned with the headlight sucking up enough power to degrade the starter's efforts. The rig's car-sized battery can cope.
Gonna put the tank & seat back on and try another road test this afternoon.

[TopCatGr58]

Hey Fred,

Glad you were able to get it to work with the Bypass, but that doesn't necessarily mean that the relay itself was bad. The DIODE converts the AC pulses from 1 of the phases/legs of the ALT charging current into pulsed DC going to the relay, but once the relay is thrown/latched, the pulsed lined doesn't do anything else. So...it could still have been a bad DIODE preventing the pulsed DC getting to the relay. But like you said, Car battery in the sidecar, no worries for starting power....plug and play!!

T.C.