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1972 Yamaha CT2 blows fuse when using the back break

01 Aug 2020 11:54
brad.lowry@att.net
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1972 Yamaha CT2 blows fuse when using the back break #1
I have a 1972 Yamaha 175CT-2. My only problem is I blow a fuse when I press my back break light. I checked the break light switch and it is hot on the bottom when it is activated. Of course it goes to ground thru the attached spring & linkage bar. Then the fuse blows.
If I disconnect the linkage and pull the switch bar from the bottom to activate it the break light works fine since it is not touching the frame.
Could the problem be a wire fault?

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01 Aug 2020 13:21
Gr8uncleal
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1972 Yamaha CT2 blows fuse when using the back break #2
I don't think that the switch should be earthed anywhere - brown wire is "switched" positive, yellow goes to tail bulb and this picks up its own earth from the black wire.

Maybe buy a replacement switch - they are quite cheap.

Please wait for others to confirm though.

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01 Aug 2020 14:14
MarkT
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1972 Yamaha CT2 blows fuse when using the back break #3
I agree. Sounds like bad switch. Should only connect power wire to bulb wire and not ground anything.

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

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01 Aug 2020 15:30
brad.lowry@att.net
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1972 Yamaha CT2 blows fuse when using the back break #4
I will get another one. My original broke in half so I got another off the internet. It hadn’t worked in a while. I assumed the new one would be good.
I think you are right. The new one has 6 volts on the bottom which I do not think is right. Probably a defective new one from the start. I’ll order now and when I get it I’ll see if that fixes it.

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02 Aug 2020 02:17
Mauser
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1972 Yamaha CT2 blows fuse when using the back break #5
As above really, rear brake light should have power to it all the time, when you press the pedal it takes the return or the negative down to earth, but the switch should just be that a switch 2 wires one from light into the switch and the other side of to the bikes earth points within the loom.....
I'm surprised the switch actually blows a fuse ?, if it shorted out the light would simple be on all the time ?.
If some part of the switches internals or the wiring was shortening out again the light would come on ?.
I would have thought our electrical expert Mark would chip in further :)

Yamaha RT2 360 ~ Honda XR650R ~ Yamaha DT175MX ~ Kawasaki KH400

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07 Aug 2020 16:04
brad.lowry@att.net
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1972 Yamaha CT2 blows fuse when using the back break #6
I just got a replacement brake switch that is an original and it worked. Who would have thought that a new switch was bad . I took the new one apart and the plunger that pulls down was cheap and the brass clip on it was loose so it just slipped to the top of the switch and made the plunger hot, which in turn went to ground down thru the lever to the break.
I’m good to go now. A bike that is restored to original that should pass inspection. It runs well. I do have a hard time finding a 10 amp fuse for it so I had to put a new fuse holder on it to fit the longer 10 amp fuses of today. Wish I could find a 10 amp fuse to fit the original fuse holder? I would swap it back out.

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07 Aug 2020 17:30
Crowvet
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1972 Yamaha CT2 blows fuse when using the back break #7
Do you happen to have the # of the original fuse? I had a an auto repair shop for 43 years and have a pretty good assortment left. They are getting picked through, but I would be happy to look for you.
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07 Aug 2020 19:29
brad.lowry@att.net
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1972 Yamaha CT2 blows fuse when using the back break #8
I looked at it with a magnifying glass and all it say is 10 A on it.
I measured it at 1/4 by 15/16 of an inch. I think it is in MM cause it measure 6 by 25 mm as shown on the attached photo.

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07 Aug 2020 23:24
Gr8uncleal
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1972 Yamaha CT2 blows fuse when using the back break #9

brad.lowry@att.net wrote: I just got a replacement brake switch that is an original and it worked. Who would have thought that a new switch was bad . I took the new one apart and the plunger that pulls down was cheap and the brass clip on it was loose so it just slipped to the top of the switch and made the plunger hot, which in turn went to ground down thru the lever to the break.
I’m good to go now. A bike that is restored to original that should pass inspection. It runs well. I do have a hard time finding a 10 amp fuse for it so I had to put a new fuse holder on it to fit the longer 10 amp fuses of today. Wish I could find a 10 amp fuse to fit the original fuse holder? I would swap it back out.


Glad you got it sorted and that it was a straightforward fix. Not so glad that a new part that you bought was bad though.

I have heard of some folks fitting a more modern type of fuse holder that takes the spade type fuses found on cars. I've not tried it myself and accept that this removes a little of the originality.

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08 Aug 2020 08:03
MarkT
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1972 Yamaha CT2 blows fuse when using the back break #10
Yamaha still sells the fuse holders and fuses. Any dealer should have one.

Cheaper to buy a new fuse holder from Yamaha as it comes with two fuses. (or at least they used to)

Let me check and see if I can find an aftermarket part number... someplace I have a little box of fuses I got at an electronics store that were the same size.

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
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