Lighting issue.

[electric_monk]

Last week on the way in to work my 1989 R100gs developed a problem with the headlights.
At about 75 on the motorway the headlight started flickering on and off, I pulled off at the next junction to investigate only for normal service to resume. So I continued back onto the motorway only for the problem to reappear when motorway speed was attained, the light eventually failed completely. Pulled over and checked connector on headlight and changed to my spare bulb. While stationary everything was fine but once I moved off the problem recurred and the light went out completely again, by this time it was now daylight so I could continue.
This morning was the first I have been able to look at the bike since, fuses fine, wiring seems fine. Lights are working until engine speed gets up to and stays at around 4000 rpm.
Any ideas as to likely culprits?

 

[Kenny]

You will literally have to 'wiggle' the wiring to see where the loose/broken wire/connection is. One of those PIA jobs to detect ! Clean any connections/relay tabs etc

 

[B Murr]

I had a faired Kawasaki gt750 with a birds nest of wires in the fairing. Piggy back connectors were the usual culprit. Similar symptoms and usually when bloody freezing and wet. I'd open and close any connectors in that circuit a few times so as to freshen them up and wear off any corrosion that might be causing the issue.

 

[DrFarkoff]

Steve Take all that schite off your key ring !!! Since 5th position is headlamp it "might" be jiggling off a wee hair

and check the connections on the base of the Ignition switch Which are most likely offenders

 

[electric_monk]

Looks like it was the relay, probably the original one in it.