Moto Grand Prix
Main Motorcycle: 1973 Triumph TR7RV
Join Date: Oct 2013
Location: Pleasant Hill, CA USA
Other Motorcycle: 1964 Triumph Mountain Cub
Hi Woodsie, There are different flashers that can be constructed different ways.
For my '73 Tiger I have 2 Emgo flashers 99-1201 on my bench. I have some genuine old Lucas, I can dig them out tomorrow if you want. Until I get the Lucas out & look at it I don't know if Lucas is same as Emgo or not.
On the Emgo if you take the cover off you'll see a sheet metal bimetallic spring unit with a wire wound resistor spot welded to it. This is the heating element. The wire is very thin, like a human hair. It seems common for this wire to be loose in, or dethatched from its crimp. Of course this is open circuit & will test infinity with ohm meter or zero volts. Nichrome wire doesn't take solder well, so to repair you can recrimp it.
In a round about way each end of the resistor is hooked to the spade terminals, so when you power flasher the current flows through resistor into bulbs which heats resistor Bending the bimetallic strip which brings together the contact points. When points come together the resistor is effectively by passed by the points so current flow goes through points & powers bulbs. This cools bimetal & the points open again. This heating/cooling cycle is what causes the flash.
On the bench I find the ohms on these 45-51 ohms. I have no spec that's what I read. So If you put ohm meter across them you get the resistance of the heater coil resistor.
When putting 12v through flasher with volt meter you are passing just volts (only a trace of current) so it basically reads battery voltage. That is what mine read. Reversing polarity doesn't matter, mine read the same.
With one spade on battery & test light with 3w bulb I can feel the resistor warm, but not enough to move bimetal strip.
So the only way to truly test these flashers is under the load of two 21w bulbs & a 3w pilot bulb powered by a good battery. Sometimes flasher my pass ohm & volt tests, yet won't flash. I can help it with my finger & it may work awhile, but not reliably. I don't know why they do this. I've not been able to fix one of these. The bimetal strip has a special bow to it that's in sort of a bind such when it heats it pops over quickly, cooling pops back.
Both these flashers were basically new. Both had the resistor wire loose or completely disconnected at the "L" terminal.
I'll try to dig out my original from new one & see how it's made. You've inspired me to finish my turn signal flasher test board. I'll finish it this week also.