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post #1 of 11 (permalink) Old 09-08-2019, 09:48 PM Thread Starter
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flasher unit testing

Using a multi meter, should I get a resistance reading when testing across the two terminals on a generic flasher unit. Set on ohms. Thanks.
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post #2 of 11 (permalink) Old 09-08-2019, 10:08 PM
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It should be open....so no circuit if its a bi metal type unit and there is no power to it.

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(Where women blow and men chunder).
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post #3 of 11 (permalink) Old 09-08-2019, 11:11 PM Thread Starter
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Thanks for that. So when 12v is applied to one of the terminals what should I expect to see at the other terminal?
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post #4 of 11 (permalink) Old 09-09-2019, 02:45 AM
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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.
Don
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post #5 of 11 (permalink) Old 09-09-2019, 03:59 PM Thread Starter
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Thank you for the explanation Don. Appreciate it.
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post #6 of 11 (permalink) Old 09-09-2019, 06:38 PM
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Hi 79woodsie, I got the bad 1973 Lucas flasher out & took it apart. Very different construction. Mind you it was bad. Looks like points were welded together, but not sure yet. I got same part # new from dealer back in 1975 ish & that flasher is still working today.

Looking at the Lucas, the resistor/heater is a single blade of material. It was stuck to the copper rivet head looking part. I separated it & it might work now??

On this flasher prior to separation it read .4 ohm. After separating it read .8 ohm. Trying to measure the resistor strip itself was odd. 2.3 ohm. I don't think any of these values are actually meaningful.... so put no value to them.

Parts may have broken off & are missing from the lucas. However from what I see.... There is a hardened contact on the tiny flat resistor wire that always contacts the copper rivet head when bimetal is cold. When hot, the contact separates from the rivet end as the bimetal moves away. This breaks the circuit & it cools. Cycle is repeated.

So it looks like all the current to bulbs is carried through the resistor strip. There are no separate contact points I can see like the emgo uses.

Again, this is a bad flasher & parts are missing so take all this with a grain of salt. I'll know more when I make the test board. Of course I could just put on bike, but I don't want to even touch the one in there now.

I'll keep you posted on what happens with the 3 flashers I have on hand using test board.

More importantly what are you getting on your tests? What was your symptoms? What is part # of the relay for 1979? Exactly what relay are you using?

Looking very closely on the Lucas flasher you can see the tiny silver resistor/heater strip that is installed on bimetal. There is a very tiny air gap between resistor & bimetal. Maybe .001-.002". The resistor is on attached at each end so current flow goes both ways from points to bimetal plate, which is ultimately riveted to the spade connector.

Don
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post #7 of 11 (permalink) Old 09-10-2019, 03:27 PM Thread Starter
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Don, I had to install turn signals on a BSA B44 to be street legal. I wired the bike up, bought a 12v flasher unit from the auto parts store. Flashers did not work, they do light up with no flasher unit installed. I think I got a dud flasher unit. I get zero continuity through it, voltage can be applied to one side and no voltage comes out the other side so I will get a different unit. It will be taking a look inside this one. Thanks
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post #8 of 11 (permalink) Old 09-10-2019, 04:31 PM
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Coincidentally, I received my brand new Lucas flasher unit (SBF114) today. Measuring across the two terminals (marked B and L) I get 36.5 ohms.
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post #9 of 11 (permalink) Old 09-11-2019, 11:34 PM Thread Starter
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Opened up my flasher unit and there is an extremely thin wire that is detached at one end. It looks thinner than the emgo unit.
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post #10 of 11 (permalink) Old 09-12-2019, 03:04 AM
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I gave up on Lucas turn signal units...they always end up with water in them and fail. The last one I even smeared silastic around the top and it still failed. And its upside down so I have no idea why water etc would even want to get in there.

I have been using these units:
https://www.ebay.com.au/itm/Motorbik...8AAOSw2idbLTUR

they are a 1/3rd of the price and work fine. I'd never go back to Lucas or any of the other similar versions again, big clunky things on a spring mount...dinosaur stuff.

tridentt150v,
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(Where women blow and men chunder).

Last edited by tridentt150v; 09-12-2019 at 03:07 AM.
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