Headlamp stopped working

JJs80XS

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Hi! 1980 XS650SG. The headlamp has been working fine. Then the other day I unhooked the bulb from the 3-prong connector to do some other work behind the light. Forgot to turn off ignition switch, and somehow blew the headlamp fuse. The fuse REALLY blew. Like, all black and smoky. Put in a new fuse, and now headlamp doesn't work.

So, did I fry something else when I blew that fuse? Headlamp had been fine up until this incident, so I don't think it is the switch, RLD, bad ground, or other common issue. Getting 0 volts out of low beam and hi beam wires. There is a solid 12+ volts on both sides of the headlamp fuse. Headlamp works when rigged directly to battery, so it is not the bulb.

Thanks for any thoughts/help!
 
Safety relay automatically turns the headlight on when the engine fires, or is there is enough volts through the circuit to trigger the headlight relay from the kick-start or electric start...........

RLU controls the power to the headlight high/low beam, turns the other one on automatically if one of the filaments blow.........

So check the RLU then safety relay.......

make sure you haven't fried or damaged the coils. leaving the key on, it has been mentioned.

Pamcopete,......OK. This question has been asked before, so here is the answer. 12 minutes. That's the time it takes for the coil to get to a temperature of 125 F, which is about 10F higher than it would get to with the engine running. That is also starting off at room temperature, so probably no more than 10 minutes if the coil is already warmed up from the engine running. This is not the time to destruction. Just the time to a particular temperature above normal operating temperature. The transistor in the PAMCO never got above 90F and it is rated for 347F, so no worries there. It's the coil that would eventually fry, and if it shorts out as well, then it may take the PAMCO with it.
Not leaving the ignition on is also an issue with points if you are unlucky enough to have a set of points closed when you turn on the power. Same is true with the PAMCO. The coil is only on for 120/360 = 33% of the time, so,
If you are dong some other work on the electrical system that requires power to be on, then just turn off the kill switch and you can leave the ignition switch on till the battery dies.
 
Are the other electrical circuits working e.g. ignition, indicators, horn, tail light and instrument lights? Does the motor start? There may just be a short in the lighting circuit from the fuse via the switches to the bulb? Check behind the head light for any burn marks, perhaps the Hi or Lo wire has worn insulation and shorted. A bad short could burn the wire right the way through and leave it looking intact just held together by a bit of the insulation. Maybe you created a direct short from +ve to ground accidentially. Are the rubber gromets missing on the head light bucket so the wires are shorting against the bucket?

Try to work out what is working and then what isn't may be more clear.
 
Have you hooked the headlight straight to the battery to make sure its not burnt out?
 
No light when the bike is running. All other electrical items working--starter, turn signals, brake lights, etc. Grommets are good. Headlight works when rigged directly to battery. I'll check the safety relay and RLU. Can't see any burnt wires, but will keep looking.

How do I ensure the safety relay and RLU are working? Lighting diagram attached to keep us all on the same page.
80_xs650g-png.116688
 
Headlight power is sent to the safety relay on a red/yellow wire from the headlight fuse. Once the relay is triggered (engine started), headlight power flows out on the blue/black wire to the RLU. On it's way there, the wire splits and runs up to power the instrument illumination bulbs. Are they working? That will verify power is coming through, or you can just test the blue/black wire. At the RLU, power on the blue/black wire is transferred to either the blue/yellow (headlight good) or blue/green (one beam burned out) and sent up to the hi/lo switch. If this all checks out then the issue has to be with the hi/lo switch or it's connections.
 
Headlight power is sent to the safety relay on a red/yellow wire from the headlight fuse. Once the relay is triggered (engine started), headlight power flows out on the blue/black wire to the RLU. On it's way there, the wire splits and runs up to power the instrument illumination bulbs. Are they working? That will verify power is coming through, or you can just test the blue/black wire. At the RLU, power on the blue/black wire is transferred to either the blue/yellow (headlight good) or blue/green (one beam burned out) and sent up to the hi/lo switch. If this all checks out then the issue has to be with the hi/lo switch or it's connections.
Awesome, thanks! I'll check those wires and lights later today and post findings.
 
Hey all, thanks for the help! Problem fixed. The badly blown fuse/short circuit coincided with the non-functioning headlamp, but was not the cause of it. Turns out one of my alternator brushes had come loose and the lamp was not receiving power from the alternator/stator. Secured the brush and it's up and running. Still learned some stuff in the process. Thanks again!
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