R100gs ignition help required

[Brokenspanner]

Hi,
1990 r100gs bumblebee
It’s new to me.
Had videos of it running and test rode it with no issues.

Got it home and turned ignition on, power died after couple seconds , turned key on and off multiple times with nothing at all, fuses checked , harness and ignition wiggled still nothing.
Took a video and sent to previous owner ( he was great and no reason to think I’ve been sold a dud), while waiting for a reply I had a cuppa and several biscuits , went back into garage turned key and everything turned on as it should , I’d touched nothing .

Key on and off maybe 50 times and it’s worked perfect every time , ignition on and I wiggled anything that would wiggle and it was fine it never went off again.

Couple days later I went back into garage and key in , seconds later all power lost.
Battery and fuses ok.
Nothing has been touched.

Dismantled cowl and removed switch.
Checks out on with multimeter continuity check.
Constant 12v live to ignition.

Cleaned all terminals and put back together , nothing.

Apart again and re checked with multimeter then plugged back in, turned key and it lit up for a second then went off.

Absolutely stumped now.

Any ideas what to try next please .

 

[Posh Pete]

Engine kill switch? Gearbox/ clutch interlock?

 

[Brokenspanner]

Engine kill switch? Gearbox interlock?

Hi Pete,

I’ve flicked the kill switch back and forth and it’s not made any difference, there is nothing ligting up at the ignition at all when I turn the key.

Not sure what the gearbox interlock is I’ll have to google that one

 

[Posh Pete]

Hi Pete,

I’ve flicked the kill switch back and forth and it’s not made any difference, there is nothing ligting up at the ignition at all when I turn the key.

Not sure what the gearbox interlock is I’ll have to google that one

Pull the clutch in. See if it makes a difference.

Have you checked the main earth at the gearbox?

 

[Brokenspanner]

The ignition was coming on perfect without the clutch being pulled , like i say I’ve touched nothing and it just stopped working then it started and now again it’s stopped.

No I’ve not checked that yet (good call), I’ve came inside for a warm as it’s bastard freezing in Stanley

 

[Gelandestrasse]

This could be corrosion in the main battery line to the starter relay - small current ok, when you up the demand the corrosion chokes it as the cable heats up. There are 2 cables from the battery, the big meaty one that goes straight to the starter and another smaller one that splits into 4 via a crimp deep in the harness. Check them both. And also check the main earth line from the battery to the gearbox. Don't just check continuity (you've done that) - take them off and give them a good bending about to see if corrosion comes out.

Failing that you could have a dodgy ignition switch (they wear and then fall apart). You can check this by, next time you get no power, check for power into it (via one of the 4 red offshoots mentioned above) which comes via an in-line plug/socket around the headstock area, and check ignition-switched power out (green) which can be traced to the coil via the handlebar kill switch.

GLWS (s being search!)

 

[DrFarkoff]

Wiggle the loom from the battery up

If yours is the same as mine 88 -91 (metal tank small cowl on round headlamp there are 3 (I think) positive connections

I had to remake them all, they were full of Verdigris

 

[Brokenspanner]

Tried to add a pic but I’m shit and can’t do it.
Pluggged ignition back together and turned it on, been round the bike and wiggled all I could wiggle …..then click and nuts came.
There is a ducky wire under the yellow starter solenoid, when I wiggle it the ignition is on and off .
I think I may have found the bastard issue .
Many thanks to all that read my drivel and offered pointers

 

[Brokenspanner]

Wiggle the loom from the battery up

If yours is the same as mine 88 -91 (metal tank small cowl on round headlamp there are 3 (I think) positive connections

I had to remake them all, they were full of Verdigris

Yeah mines a 1990 small cowl , wiggled and wiggled and found it

 

[Brokenspanner]

This could be corrosion in the main battery line to the starter relay - small current ok, when you up the demand the corrosion chokes it as the cable heats up. There are 2 cables from the battery, the big meaty one that goes straight to the starter and another smaller one that splits into 4 via a crimp deep in the harness. Check them both. And also check the main earth line from the battery to the gearbox. Don't just check continuity (you've done that) - take them off and give them a good bending about to see if corrosion comes out.

Failing that you could have a dodgy ignition switch (they wear and then fall apart). You can check this by, next time you get no power, check for power into it (via one of the 4 red offshoots mentioned above) which comes via an in-line plug/socket around the headstock area, and check ignition-switched power out (green) which can be traced to the coil via the handlebar kill switch.

GLWS (s being search!)

Cheers I seem to have found it

 

[Brokenspanner]

Pull the clutch in. See if it makes a difference.

Have you checked the main earth at the gearbox?

Think it’s now sorted

 

[Posh Pete]

Think it’s now sorted

If it's the earth, there's often an issue due to ham fisted over tightening of the 10mm bolt at the gearbox. An option is to lift the tank and earth the battery direct to the frame under the tank.

 

[Brokenspanner]

If it's the earth, there's often an issue due to ham fisted over tightening of the 10mm bolt at the gearbox. An option is to lift the tank and earth the battery direct to the frame under the tank.

Looked at that earth and it looks like it could do with a clean over, it’s secure but some fine corrosion on it. I’ll clean it off and rub the face down when I tidy that broken wire up.
There are a few bits I’ll have to “adjust” but that’s all part of an old bike

 

[Bubb]

Sounds like you’ve found the problem, and it’s fixed…for now.
You can get a new harness for the Gs from motorworks if you want to fix all the possible wiring problems on an old bike.
It’s worth going through all the connector blocks too…. Small file on the contacts and dialectic grease to keep the corrosion at bay.
It’s a fiddly job, and takes time, but worth it imho.

 

[Gelandestrasse]

Sounds like you’ve found the problem, and it’s fixed…for now.
You can get a new harness for the Gs from motorworks if you want to fix all the possible wiring problems on an old bike.
It’s worth going through all the connector blocks too…. Small file on the contacts and dialectic grease to keep the corrosion at bay.
It’s a fiddly job, and takes time, but worth it imho.

You may be able to get a brand new harness off BMW. I did this for my 1991 GSPD and the bMW one was cheaper than the repro offered by Motorworks.

 

[mikeyboy]

Sounds like you’ve found the problem, and it’s fixed…for now.
You can get a new harness for the Gs from motorworks if you want to fix all the possible wiring problems on an old bike.
It’s worth going through all the connector blocks too…. Small file on the contacts and dialectic grease to keep the corrosion at bay.
It’s a fiddly job, and takes time, but worth it imho.

I’d need to check with Charlie but ,the motorworks listed part is not correct for the round headlamp GS.
The only solution he found was to fit a G/s one and modify for the differing fusebox and rear lamp connector.
We fit a new loom wherever it’s possible these days as it’s the most likely source of hassle on older bikes,
Especially when they’ve had 30 years plus of owner errrrm add ons

 

[Brokenspanner]

Sounds like you’ve found the problem, and it’s fixed…for now.
You can get a new harness for the Gs from motorworks if you want to fix all the possible wiring problems on an old bike.
It’s worth going through all the connector blocks too…. Small file on the contacts and dialectic grease to keep the corrosion at bay.
It’s a fiddly job, and takes time, but worth it imho.

It’s not quite there yet but some head scratching has gone on up to now.

 

[Steptoe]

Especially when they’ve had 30 years plus of owner errrrm add ons

Funny that, read the 1100/1150 section and almost all the electrical problems are caused by owner add on’s and electrical “improvements”