Strange turn signal/indicator behavior

Woody850 · Tuesday at 1:13 AM

After the loss of power to the LH Rear indicator which was traced to a broken wire in the tail light cowling the now function of the indicators on activation is a rapid flash. This is for both left and right. If the indicator switch is set to of and then switched back to the said indicator it then blinks normally.
Fitted is the original blue (can we call it relay?) can on the spring.
I see AN sell a capacitor as replacement for this item, but my problem is I am planning to do a three day tour as of Friday.
Any indication to how to solve this problem would be gratefully accepted.

L.A.B. · Tuesday at 1:18 AM

Woody850 said:
Fitted is the original blue (can we call it relay?) can on the spring.

What is generally referred to as the blue can is the 2MC emergency starting capacitor not the flasher relay.

Woody850 · Tuesday at 1:30 AM

I see now and in the book 'Flasher Unit Lucas Type 8FL' could eventually be the culprit, but where is it located?

L.A.B. · Tuesday at 1:34 AM

Usually on the back plate of the frame or the plate attached to it depending on the model (not 850 Mk3).

Woody850 · Tuesday at 1:51 AM

Thank you, it is a 1973 850 Roadster. I will have a look as soon as a supplier has called back.

L.A.B. · Tuesday at 2:16 AM

Switch the indicators on and follow the clicks. It should have a double white and a light green/brown wire attached.

concours · Tuesday at 3:17 AM

Rapid flashing is caused by excessive Current draw, so a partial short circuit could cause that,. Because it displays intermittent symptom I would look to the handlebar switch, or, the flasher itself as you have suspected.

Also, be sure you didn't accidentally create an intermittent Short while affecting the repair in the tail light CowL.

Woody850 · 2026-06-18T06:24:45-0600

Thank you all for your help! Swapping the flasher relay to one I had in my toolbox proved fruitless, but once recieving the original from a dealer in Austria the problem was solved. You can imagine how happy I was.

concours · 2026-06-18T07:28:59-0600

Woody850 said:
Thank you all for your help! Swapping the flasher relay to one I had in my toolbox proved fruitless, but once recieving the original from a dealer in Austria the problem was solved. You can imagine how happy I was.

Thank you for closing that loop. This thread can help others in the future…

Tornado · 2026-06-18T10:39:27-0600

Woody850 said:
Thank you all for your help! Swapping the flasher relay to one I had in my toolbox proved fruitless, but once recieving the original from a dealer in Austria the problem was solved. You can imagine how happy I was.

Not sure why a modern flasher would not solve issue when a new old type did? Modern two conection types shouldand do perform well on these bikes.

nortonmargie · 2026-06-18T22:19:31-0600

Tornado said:
Not sure why a modern flasher would not solve issue when a new old type did? Modern two conection types shouldand do perform well on these bikes.

Nortons work in mysterious ways...

concours · 2026-06-19T04:34:30-0600

Tornado said:
Not sure why a modern flasher would not solve issue when a new old type did? Modern two conection types shouldand do perform well on these bikes.

He never said modern.

Could have been a duff one, or of incorrect rating that was lying in state toolbox

kommando · 2026-06-19T04:48:32-0600

Modern ones work on voltage rather than the heated bimetallic strip in the old Lucas originals which needed amps, so an improvement. But modern ones are negative earth so you either buy a modern one for positive earth or do some fancy wiring to fool the modern one.

But sometimes clockwork is best

414: Mechanical clockwork flasher unit - Self cancelling for Classic & Vintage Cars | Vintage Supplies | Classic Bulbs

Clockwork panel mounted flasher unit/indicator switch (suitable for 6, 12 or 24 volt systems), makes and breaks contacts for approximately 20-25

www.classicbulbs.co.uk

Tornado · 2026-06-19T12:37:48-0600

kommando said:
Modern ones work on voltage rather than the heated bimetallic strip in the old Lucas originals which needed amps, so an improvement. But modern ones are negative earth so you either buy a modern one for positive earth or do some fancy wiring to fool the modern one.

But sometimes clockwork is best

414: Mechanical clockwork flasher unit - Self cancelling for Classic & Vintage Cars | Vintage Supplies | Classic Bulbs

Clockwork panel mounted flasher unit/indicator switch (suitable for 6, 12 or 24 volt systems), makes and breaks contacts for approximately 20-25

www.classicbulbs.co.uk

No thats not true. Modern two connector flashers work just fine on positive or neg earth...there are modern ones that still use a bi-metallic strip that heats up. There are also full electronic ones that function as you describe but will operate fine with either polarity...just switch the two connections if needed. LED compatible types also are fine on positive earth.

Strange turn signal/indicator behavior

Woody850

L.A.B.

Moderator

Woody850

L.A.B.

Moderator

Woody850

L.A.B.

Moderator

concours

Woody850

concours

Tornado

nortonmargie

concours

kommando

414: Mechanical clockwork flasher unit - Self cancelling for Classic & Vintage Cars | Vintage Supplies | Classic Bulbs

Tornado

414: Mechanical clockwork flasher unit - Self cancelling for Classic & Vintage Cars | Vintage Supplies | Classic Bulbs

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