Hi Colin. I have just been out to look at a spare trafficator. On the sample I have, the moving arm has a small protruding stepped steel peg about 3/8 inch from the hinge pin, and this comes to rest on the upper fixed diecast frame (above the solenoid) to limit the travel. Maybe your pin is worn/missing or the diecast part is worn ? Because of the leverage, a little wear can have quite an effect. I don't know if you have done a road test but you might well find that on the road there is enough vibration to make it drop down anyway.

Usually, the problem is getting the wretched things to go up rather than come down (stop smirking at the back !) because of wear or friction, so cleaning and light oiling helps. When bench testing it may be more realistic to use 7 volts rather than 6 volts, as the higher voltage is nearer what it will be getting on the road when the engine is running and the battery is being charged.

Location: New Forest

Thank you John.
I will take it off again and adjust it.