Ignition problem 1982 R100RSR

[Jpf]

Hi there,

Can anybody help solve this problem?

The bike is a 1982 R100RSR

When I turn the ignition key off the engine keeps running.

I stop it using the kill button then isolate the power by disconnecting the battery earth.

When I reconnect the battery lead everything is OK - as it should be - ignition works OK until I need to stop the engine .....

Seems that when the ignition is turned on, something is energised and stays energised until the battery is disconnected.

So far no one has been able to shed a light on this.

Thanks

James Farley

[jono]

Has your bike recently developed this problem or has it been like this since you acquired it?

If its a recent development, have you been into the wiring specifically the ignition switch or changed any relays?

Should be straight forward to isolate and resolve at a Tuning day, with a wiring diagram and a volt meter.

The R100RS runs power from the battery through the starter relay to the ignition, the headlight relay and the clock, so all 3 have direct power supply as long as the battery is connected.
The Kill switch is wired to the ignition and the starter relay, coil and the ignition control unit. switching ignition off should do the same as activating the kill switch. It sounds like this step is where things go wrong.

My first suspect would be ignition incorrectly wired resulting in the ignition circuit remaining open

Second thought would be an incorrect relay installed in the starter relay circuit, the different years and models use different relays and these look similar but work differently

Those off the cuff thoughts hope they help.

[Jpf]

Thanks for your input Jono.

This problem started recently.

All wiring is OEM and has not been interfered with.

The main diode board was replaced about three months ago.

It has also been suggested that there may be a faulty diode in the headlamp .....

Stay upright

James Farley

[wightman]

Hi James

I've had an RS for the last 30 years and never heard or seen this one. Have you tried to change the ignition switch, to rule out that one first? It's a quick job to do. A much more common problem is the cubic brown relay under the petrol tank gets corroded terminals and the exact opposite problem occurs. Lights on at the dash but no power to the starter motor.

[Jpf]

Hi John,

The ignition switch was changed quite a few years ago.

My immediate thought was the ignition switch ....

But everything works normally when the power has been interrupted .... ie the battery has been disconnected then reconnected ....

Some how I do not think the switch is the problem - I hope not as they are not available ....

Stay upright

Jim

[jono]

Quote found on the net http://bmwmotorcycletech.info/startingprobs.htm

20. In 1978, BMW changed things again. This lasted into 1980. BMW added 2 diodes...and a switch! These models had an under-fuel-tank brake master cylinder. BMW incorporated a low brake fluid level switch, which, when closed, turned on a brake failure RED light. The switch was wired to that lamp, and via a diode to the starter relay coil. This modification did NOT interfere with the starter operation, even if the diode failed in the open condition. If, however, that diode shorted (HIGHLY unusual), and at the same time one had a failed (closed) switch, or the level was low, the starter could fire up, mysteriously, all by itself, and NOT release!...unless the ignition or kill switch was used.

21. BMW added a diode in the headlight relay. The location of that relay varies with year and model. The wiring and operation was such that during the time the starter motor was powered, the headlight relay coil was NOT energized, which turned off the headlight. Depending on model, whether USA or European, this varied somewhat, and in most models... the instruments and rear running lamp WERE left ON during cranking; by use of the diode inside the headlight relay. Some had various combinations. What is complicating the mess here, is that, at least for USA models, the diode in the headlight relay was so connected that if it SHORTED, then in some conditions of ignition switch setting, etc., it was possible for the starter relay to fire up, and NOT be releasable, until the battery was disconnected. Yes, the same sort of thing like the 1978-1980 symptom of the shorted starter relay diode. Thus the same SORT (nearly) fault could be had via a shorted headlight relay diode or shorted starter relay diode!

Theoretically this problem could only happen in the PARK position of the ignition switch. The fuse was also now incorporated in the headlight relay section, and also fed the parking light. Normally, if you used the starter button, even if the fluid level was fine, the brake failure light would illuminate at every start...this tested that lamp at each startup. It wasn't necessary to have the fluid be low, then, to turn on that lamp.

22. With the 1981 models, no longer was there an under-tank master cylinder, so the operation is slightly simplified. The wiring is exactly the same, but withOUT the master cylinder switch and, of course, its diode was eliminated. This lasted through the 1984 models.

23. There were several more variations and changes until the end of production. In 1985 and later, BMW put the starter button into the + power feed to the starter relay coil, and the negative side of that starter relay coil went to the same diode and the same neutral switch and clutch switch as before. By moving the position of the starter button connection, BMW could incorporate the diode into the relay housing. BMW also added another diode in the headlight relay area; this time in series with its coil. The starter worked the same, however.

Can you pick which variation you have and if you have a diode that may have shorted?

[Jpf]

Thanks Jono,

Will be taking a close look at things on Thursday evening.

Will let you know what we find.

James

[Jpf]

Hi All,

After a a lengthy trial and error search we found that the problem was with the hazards lights circuit - more than likely the switch.

With a wire disconnected from the hazard lights relay everything works OK.

One to remember.

Thanks for the input.

James R100RSR Farley