I am a happy owner of FLHTC 1990, and since the bike was bought from the 2nd owner it has always been that whenever the left or right turn lights are engaged then voltmeter also flashes. I just got a new original battery from the dealer here in Copenhagen but the problem is still there.

Is that how it should be or what is wrong and how can it be fixed. Any suggestions are heartilly welcomed.

 

check your ground that it is clean and tight both on the battery on the chassis that's the 1st thing

 

Thanks It has been checked and cleaned but the problem is still there. Any more inputs???

 

You have a high resistance connection somewhere in the circuit, a partially broken wire, under sized wire or a weak battery/charging system.

You could temporarily connect the voltmeter across the battery and convince yourself that the meters reads a steady voltage when the turn sighals flash. If the meter is steady, start looking for a high resistance connection between the battery and the original voltmeter connection.

 

Your voltmeter is telling you that the ignition switch is getting weak on the accessory side.

I bet it jumps bad when you hit the brakes and probably dances even when the radio hits a loud bass note.... Those switches are no longer avaliable and if you find an NOS switch - they are expensive!!! A used one will likely have the same problem.

Install a relay (under the seat) that will be triggered by the ignition switch and fed at the main breaker. I won't try to explain the details of this procedure unless asked, but I've done many like that....