Electrical Power Loss R100rs
 

I've had a recurring problem over the years, usually when the battery is fairly low on charge, or being used without the engine running.

When I turn the headlights on all electrical power - even the clock - dies. This happened recently on tickover which killed the engine, and could have been very dangerous.

I can hear the headlight relay click and I guess this is the source of the problem, however I would appreciate any advice before I meddle!

Julian Delaney

Check the main ground strap between battery and frame including the terminals. Do the same for the live feed especially the heavy duty cable that goes to the starter motor. check also there is no fraying of the insulation.

Thanks I'll have a look tomorrow.

Cheers Julian

sounds more like a serious short than a loose ground...

When you turn on the headlight all you do is to flipp a switch on the handle. This just activates a relay inside the headlight.
It is simply not possible that that action kills the ignition...
To kill the ignition you need to hit the kill-button...

Then there is the posibility that there are several issuse happening at the same time - a freak coinsidens.

Damage wires to the coils can cause a turn off of ignition, as can a loose ground to the coils.
The coils are grounded to the frame and via the rev-counter.

The key problem is however that most/all electricity is turned off when you switch the headlights on - this can happen if your fuses are gone inside the headlight and someone have made some additional connections allowing for optional ways for the electricity to "move"... I have this on my R80...

You need to up-date the connections of the circuit board inside the headlight.
In stock/standard it lacks:
- grounding to the frame; install a ground from the circuit board to the frame, 4mm2 will do.
- check that the headlight earth (flat broad cable to the right side of the headlight) is installed; it saves the steeringhead bearings from getting "fryed".
- the 4mm2 power supply to point 30 on the circuit board was never installed at the BMW factory... install it, with a cable fuse, directly from the battery; lifts voltage to the H4 by about 3-4V and ensures power to the electrical system. (If you want the remainding 2-4V's to the H4 you need to install two new relays inside the headlight).

Begin with opening the switch on the handlebar - look for damages. It is not uncommon for them to be the cause of your problem, even though they should not cause an ignition shut down.

latest developments
 

Thanks for your advice, I've had more problems, during the MOT test, the left side fuse blew, causing numerous electrical faults.
On inspection I've fould the green cable from the ignition block to the circuit board in the headlight totally burnt out and melted to lots of other cables. I've separated the burnt cable and replaced that and the fuse, I've tried all the electrics and cannot replicate the fault.
Also now if I turn the headlight OFF, SOME of the electrics die, but not, as prevously stated, all of them. I need to check the insulation to some of the other damaged cables before I can eliminate this as a cause, but I'm a bit baffled by it.

Thanks Again for any assistance, Julian

I have sorted some of the issues, I had connected the wrong fuse cable to the circuit board, causing power to the rest of the circuits only when the lights were on. All cables replaced / repaired and everything works. My only concern is that i cannot sea any obvious cause of the initial problem, I guess that the head light bulb may have been pressing too hard on the wiring and cut throught the insulation causing a short?

regards Julian

Glad to see you are sorted, on my BMW I had the main cable from the battery to the starter motor short out during a thunderstorm. Apart from frying the wiring, it also killed a 3 months old battery. So far since 1961 that has been the only electrical breakdown I have experienced. But then all my other bike s had been Meriden Triumphs and Redditch Enfields :).

Can anybody let me know the correct ampage for the fuses, It occures to me that mine must be too high to allow cables to fry.

Thanks Julian

10A.

If I recall correctly, otherwise it is 15A.

Are you running your bike at winter?
Salt, road salt.
A damaged insulation of a cable will cause that with the nice and helpful aid of roadsalt...

Aquaintance of mine, who worked (works?) at Ericsson Mobile (car electrics - ambulances etc) installed some extra cables on my R80/7... I have melted H4 bulbs and sockets... then I checked how he had connected the fuses... in parallell... I have access of about 400-450A inside the headlight -before- any fuses blow...
Have you or previous owner tampered with the wiresystem?

It is -not- uncomming for the wires inside the main loome rounding the steeringhead to get shorted on /5-7 pre 85.

On the RT/RS there is yet a tiny snag...
The screws secruing the fairingpart above the oilcooler have a screw that hit the wireloome directly... start checking there - you might have a wire that have been damaged by that screw -:(...

Rember that BMW have installed 0.75mm2 wires where the actuall demand is minimum 1.5mm2... hence it is quite smart to install the two extra relays that I suggested inside the headlight... let me know you mail-adress so that I can send you photos of where and how to install (sorry - failed to figuree out how to post photos here... "quota filled" is all I get...).

...you are not running H4 130/90W?... that -will- burn the wire...
You should -not- use a stronger bulb than 90W/80W (which do not exist), so Phillips X-trem Power (60/55W shines like 90-100/85-90W) is the best option (way too expensive but will give off a fairly good light; no other bulbs comes even close less one chooses the rally bulbs that melt the wires, reflector and blows the fuses...)

pictures would be great, thanks my email juliandelaney@blueyonder.co.uk.

I think there has been a fair bit of fiddling the the headlight bowl before, a few connectors have been replaced before.

The replacement cable i installed is thicker than the original, hence my concern about fuses, mine are 10amp by the way.


regards Julian

...did you get any photos?

How did the conversion turn-out?