starter kicks in when I plug the head light in

[ted]

My starter kicks in when I plug the head light in ?
1980 r100 I think it was an RT at one time ---- plug for gauges
I picked this up --- drove it for two days ran good ---tune up time
changed fluids -- pulled the tank to check the brake fluid
Looks like a new master-- no history--broken coil bracket on the frame
pull coil disconnect battery---weld bracket --- put everything back together
new wire ties-- new fuel lines--back it outside fires right up--small fuel leak
fix leak -- go to start and nothing dead key --open the head light all looks good
bike starts up--plug the head light in and starter kicks in -- been playing with
this and I don't know what to try next-------- Any thoughts

[ME 109]

Can't think of too much at the moment, but the headlight and starter motor are related by means of a load shedding relay that cuts power to the headlight when the start button is pressed.
I'd look at misplaced/loose/disconnected wires, particularly ground wires associated with the starter, relay, and headlight.

[ted]

I cleaned up the ground wires --I ran an extra ground wire to the back of the head light
I didn't think of a shedding relay --- thanks for that one

[ME 109]

Try removing the new ground wire.

[ted]

I put that on after the fun started---it didn't help so it's coming off
I been playing with this off and on for three weeks

Thanks

[Airbear]

G'day Ted, and welcome aboard. Three weeks of frustration is more than enough.

The load shedding relay is called a 'Headlight Relay' in the diagrams but it does not function as a normal headlight relay (as ME109 states) - it does not supply more volts to the headlight or save your switch contacts. It is also pretty expensive. And troublesome. Also there are differences in the wiring to that relay for US vs Euro models.

Sadly, this forum does not have an 'electrical guru' posting at this time. However, if you head over to the BM Bikes and Riders forum and post your query in the Airheads Q and A section you will have access to a couple of very knowledgeable experts.

The coloured diagrams in the Haynes manual are the easiest to follow IMO. Best of luck attached.

[ted]

frustration--wish I could leave it in the garage

Thanks for your help

[gspd]

"Sadly, this forum does not have an 'electrical guru' posting at this time."

hmmm, I resemble that remark.

Should I chime in?

I can fix it if from here if you have a test light, a multimeter(volt/ohm), a bunch of jumper wires and a wiring diagram.

[ted]

a bunch of jumper wires ---you're scaring me ---I didn't think that head light needed more wires

test light and a multimeter -- and some kind of wiring diagram -- yes I do

[gspd]

OK first off, if I understand correctly, your bike starts and runs fine with the headlight removed, but when you physically connect the 3 prong headlight wiring plug to the actual bulb, the starter activates?