Hello all,

The bike: 1985 BMW K100RS

Ok, here is the drill. I bought the bike, rode it home ~80 miles or so. Everything great, everything works. The goal with this bike is to make it a basic non touring type bike, a la naked Ducati Monster style or cafe-ish. First step, ROUND HEADLIGHT.

I had a Hm headlight with bucket (H4 type bulb, 60w) and some universal brackets. Mounted the light. Everything good. Noticed some melting in the wires going to the headlight connector. I immediately pulled the shielding plastic back and started to trace the melted wires. Turns out, all 3 wires (brown/white/yellow) had melted together. The melting had stopped about mid tank in the harness. Snipped off old shit wires, crimped on new ones. I have high beam going to the wire labeled PASS on the light harness, low beam wire going to the LOW, and the ground wire into GROUND. Confirmed all fuses were good, and even replaced them anyways. Tail light works, blinkers work. Pass works, but no low or high beam. I check for 12v at the headlight harness where it connects to the light, I get a little under 12v for low, but nothing for high. Ive tried reversing the low and high wiring where it plugs into the headlight harness, no change. Pass always works though. What gives? Any advice?
Btw, I found other random melted wires once the tank was off. Some worse than others but not nearly as bad as what i found on the headlight harness. Is this common? What could have done this?

Thanks guys!

Check the relays and fuses first , next I'd check the switch on the handle bars
cheers Tony


Btw have you got a good earth ?? including the earth strap going to the handle bars

Toto_jp wrote:Check the relays and fuses first , next I'd check the switch on the handle bars
cheers Tony

\

I did check fuses, had a couple of blown fuses although not related to headlight. All fuses are good now. Why relay? The pass light works (hit the pass button on the switch, I get a beam of light). That tells me relay works for the headlight circuit. Same with fuses. I reckon the switch could be at fault, but Im getting 12v to the pigtail that connects to the light itself?

I guess the question is, what could possibly be wrong if the pass light works, but the running lights/low and high beam do not.

Switch? I also remember flipping the switch to high beam, but i did not get any signal with a voltage meter to the high beam wire.

I also went as far as adding another ground at the headlight bucket ears just in case. No change.

One of the relays is a load sharing?? relay what it does is turn the light off when you start the bike this may be burnt out fused causing it to stop the power to the light

Thanks Toto, and thanks for the reply in the other thread. Ill check those things out.

Sitting at work, thinking about working on my bike sure is a bummer.

scabzzzz wrote:I guess the question is, what could possibly be wrong if the pass light works, but the running lights/low and high beam do not.

Pass and hi/lo have different paths in the wiring system, both shares the load shedding relay.
Pass connected directly, hi/lo is connected via light on/off switch at RH switch assy.

I`ll guess the reason to your problem is the on/off switch, or its connector under the tank.

Inge K.

an under tank inspection might help scabzzz

we have seen a few instances where the cabling from the switches joins back in the loom down there have actually burnt out and shorted to other things .... but my imediate guess is the left hand switch mechanism has become faulty ....but do the under tank stuff .....to be sure what your looking at .

many of us have added relays to relieve the current requirements through the switches and cabling ....a highly recomended kit is from "eastern beaver"



hope this helps

+1 on the Eastern Beaver kit it is plug and play. Given melted wires and blown other fuses it points to there having been an "electrical incident" at some time because to melt wires it takes a fair bit of current to heat the wire up to plastic melting temperature. If you take a look at the circuit diagram that Bert produced which is made to be really easy to follow you will see how the headlight and switches are powered and can trace back to find the problem.
Regards,
K-BIKE

Thanks guys, great information.

I checked out Eastern Beaver. From what I understand, it looks like Im buying the H4 kit from them to replace the wiring from the harness box up to the headlight itself? Im electrically challenged but i'll give it a shot.
Ill go ahead and make an introduction thread too.

If you can follow a road on a map then you can follow Bert's diagram it is really just a road map of the wires that connect to the devices (places) and as he has put it into colour it makes it much easier, the official BMW diagrams are RUBBISH and yes I am shouting!
You will get there we are all here to help.
Regards,
K-BIKE

Keep at it mate, you will get there. Just a thought, the previous owner may have replaced some wiring before and changed the colour code of the wire. I have a tractor and the previous owner had rewired it with one roll of wire. Just follow the red wire!