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.

__________________
Drive Safely,
Albert

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