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I have just aquired a 1985 R100RT. When the ignition is switched on the small rectangular light below the screen (windshield) comes on, as do the warning lights
And the horn, indicators, indicator 'buzzers' and brake lights work. The headlight will not come on however unless one uses the flasher switch. The bulb has been replaced and the wiring in the headlamp seems ok. I don't have '85 wiring diagram but I don't think the lights are fused? The fuses (2) seem ok anyway. I really need to get this sorted. Could it be the relay?

It can be a number of things, but start with the simplest frist.

Unplug all connectors and clean them all. Clean and test the main wiring harnes ground. That is the brown wires that are on one of the coil mounts. Wiggle those wires while testing the headlight. If they are bad the only path to ground for the headlamp is through one of the front signal lights.

More ideas will pop up.

mimic wrote:I have just aquired a 1985 R100RT. When the ignition is switched on the small rectangular light below the screen (windshield) comes on, as do the warning lights
And the horn, indicators, indicator 'buzzers' and brake lights work. The headlight will not come on however unless one uses the flasher switch. The bulb has been replaced and the wiring in the headlamp seems ok. I don't have '85 wiring diagram but I don't think the lights are fused? The fuses (2) seem ok anyway. I really need to get this sorted. Could it be the relay?

Welcome to Boxerworks mimic.

Your '85RT will be a monolever as opposed to the earlier twin shock bikes that I'm most used to. So what I'm saying will apply to '84 and earlier bikes, and I'm guessing that the headlight circuitry hasn't changed.

With that in mind, yes it could be the headlight relay, in fact it is likely to be the relay.

What's happening is that the "flash" position supplies power to the hi beam separately from the rest of the headlight wiring. I have had to ride home in the dark with my left thumb on the "flash" button, which was the only thing that would work.

Normally, when you switch the ignition to on you will hear a clicking in the vicinity of the headlight. That would be the headlight relay doing it's job. No click points to the headlight relay, though it could be wiring associated with the realy.

On the earlier bikes the headlight relay is located in the headlight shell, behind the outer lens, and reflector. It will likely be a small silver colored relay on the L/H side of the headlight shell as you sit on the bike.

So, is this your first airhead?



Ken

Thanks for that Ken.
This is rather a convoluted story. My bud in the UK (I'm in South Africa) has 2 airheads. He wanted to come here and tour on one of them for a couple of months but was quoted an exorbitant sum to ship the bike here and back. So I looked for and found one here which was cheaper than the shipping quoted and bought it on his behalf. Unfortunately I know nothing about BMW bikes in particular having only owned British ( BSA, Velocette). The bike goes well and I have been doing cosmetic work on it prior to his arrival and only noticed a while ago that there was a problem with the lights. The guy I bought it from only had it a short while himself and never rode it in the dark! (As I discovered when I got back to him).

mimic wrote:Thanks for that Ken.
This is rather a convoluted story. My bud in the UK (I'm in South Africa) has 2 airheads. He wanted to come here and tour on one of them for a couple of months but was quoted an exorbitant sum to ship the bike here and back. So I looked for and found one here which was cheaper than the shipping quoted and bought it on his behalf. Unfortunately I know nothing about BMW bikes in particular having only owned British ( BSA, Velocette). The bike goes well and I have been doing cosmetic work on it prior to his arrival and only noticed a while ago that there was a problem with the lights. The guy I bought it from only had it a short while himself and never rode it in the dark! (As I discovered when I got back to him).

What got me into BMW's about 26 years ago was my love for British bikes, the difficulty in keeping them fit, and (in the days before internet) the difficulty in finding parts. I became interested in BMWs because of their reputation for reliability and that they resembled British bikes more than any thing else.

Later I found out that BMW's, what we now call airheads, weren't nearly as reliable as I expected them to be. But by that time their non-modern quirkiness, maintainability, parts availability, and BMW ways of doing things became "charming" in their own right.

The same might happen to you.

I still have my British bikes and a couple of them were actually running when I drifted away from them. But nowadays they are, for me, the ubiquitous "someday" projects. Still, there is nothing quite like the sound of a big open piped single on the overrun and the (opened up) megaphones on my Triumph Thunderbird. Plus they are so easy on the eyes!



Ken