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CT2/3 wire harness, continuity checking

  • Gr8uncleal
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CT2/3 wire harness, continuity checking was created by Gr8uncleal

I've just been tidying up a CT2/3 harness that came to me with some other parts. I reached the stage where I thought I'd finished and so started to test the various colours for continuity.

With my brain in RD mode, I expected to see continuity between the blue wires and the yellow wires at the front and end of the loom. However, there wasn't, and my first thought was broken wires somewhere.

Having had time for a little cogitation 

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, I'm now thinking that, if the tail light and headlight and clock illumination light are on different circuits, then I shouldn't expect to see continuity - is this correct?

Thanks.
16 Apr 2021 12:06 #1

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Replied by Andy L on topic CT2/3 wire harness, continuity checking

Err Alan, just taking your comment in isolation you are correct to NOT expect continuity between separate circuits..!!   Maybe post some more details and the forum may be able to help.  Best regards Andy.  P.S. was that liquid induced cogitation by any chance

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16 Apr 2021 14:54 #2

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Replied by Gr8uncleal on topic CT2/3 wire harness, continuity checking

Thanks Andy.

Having stripped most of the non original tape off the harness and finding no obvious breaks/damage, I looked more closely at the wires and saw that some of the same colour (ie blue and yellow) had different, independent loops. I then remembered that, on my same era DT and RTs, the headlight and clock lights only work when the engine is running, whereas the tail and brake lights run off the battery. It occurred to me that these matters are directly linked and my post was really to seek confirmation/reassurance of this.

As I said, I'm more used to arsing around with RD electrics, where you should find continuity between all wires of the same colour.
17 Apr 2021 00:22 #3

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Replied by Andy L on topic CT2/3 wire harness, continuity checking

Yep Alan I understand now. I bought an aftermarket new wiring loom for my '75 250B (not the smartest aftermarket purchase I ever made) and it took me a couple of hours testing/head scratching to determine it had two completely separate yellow wire circuits and similarly two brown circuits, so I fully see your situation.  As for your RD circuitry it does seem to make great sense, i.e. one colour for one circuit. Anyway back to your continuity checks, from my experience with the exception of the battery (leave disconnected) plug as much of bikes electrics back together when doing continuity testing. Also re-attach to the bike any fittings that earth through the frame/handlebars. Armed with the appropriate wiring diagram from the Tech library run continuity tests and mark up dia as you go.  It's surprising but gradually it will all start to make sense. The biggest mistake is pre-conceiving the results, instead ALWAYS believe the meters results. Good luck with it all. Andy.
17 Apr 2021 01:51 #4

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Replied by MarkT on topic CT2/3 wire harness, continuity checking

If you get a non-US harness or one for an earlier magneto model (earlier than about 1970), the blue for the taillight will connect to the blue for the gauge lights.

Key switches can go either way too...  sometime in the 1970 model year they made the change to run the taillight off the battery to meet the then-new US saftety law that said taillamp must remain on with engine off.
 
1963 YG1-T, 1965 MG1-T, Allstate 250, 1970 CT1b, 1971 R5, 1973 AT3MX, 1974 TS400L, 1975 RD350, 1976 DT175C, 1976 Husqvarna 250CR, 1981 DT175G, 1988 DT50, 1990 "Super" DT50, 1991 RT180, 2017 XT250
17 Apr 2021 08:20 #5

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