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1972 Yamaha LT2 - Restoring the Original Wiring

  • Zyamaha
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Hello Everyone,

I am new to this forum and have never posted here before, so forgive me if this topic has been covered before (I couldn't find anything that relates to the issue I am having).

I bought the bike about 6 months ago and it ran great, but it didn't have any turn signals or a horn. The person who owned the bike before me decided to make it a "cafe racer" style bike so they removed anything that wasn't absolutely necessary, such as what I mentioned previously. They also swapped some other parts and wiring with some more simplistic alternatives. They removed the original main ignition switch and replaced it with a generic Amazon one and also swapped the headlight to a 12v floodlight and the taillight to a 12v bulb. This bike uses a 6v system and I noticed that these did not get bright enough during the normal cruising speed, so I decided that I would convert the bike back to where it would be when it was stock.

I got everything I needed (as far as I know) which included the blinkers, headlight, taillight bulb, horn, flasher relay, battery, wiring harness, fuse, ignition switch, blinker, headlight, and horn switch. I also bought some basic 6V LEDs that I could wire up to act as a flasher indicator, neutral light, and high beam indicator. I also may have not listed all the parts I bought, since there were quite a few things it needed.

So, I used my DMM to check the wiring harness and compared it to the diagram in the manual for the bike, where I found that all of the points worked properly and did not need anything replaced. I then checked the main ignition switch to make sure that every position was connecting the proper pins so that it would be able to distribute the power properly, which it did (although it was somewhat touchy). I got the battery set up and ready to go and then connected it to the bike with the proper plugs in the harness. I connected the main ignition switch and then connected all of the rest of the components using the diagram as a guide.

Once it was all wired up, I was able to see that everything worked except for the headlight and the custom high beam indicator that I put in. I thought this was strange so I worked on troubleshooting any possible point of failure I could think of. I checked the headlight itself, which was fine. I checked to make sure that it wasn't just shorting out to the indicator, which it wasn't. I rechecked the harness to make sure that it was still getting power while the bike was running, which it was. I thought the issue could have been a bad ground, but I was unable to get the headlight to work even with a proven ground. I noticed that the taillight was working while only connected to the battery and also while the bike was running, which I did not think it was supposed to do since the diagram shows that it should only have power from the magneto and not the battery. I tried running a wire from the taillight wire in the harness to the headlight and it finally worked, proving that it is not the headlight itself.

I read through the service manual to try and find any information that could lead me to where the problem could possibly be and I landed on the magneto itself, since the yellow wire from it is supposed to power the line that goes to the headlight. I removed the magneto cover and inspected the wiring where I found that it was in semi-rough shape and thought that maybe where the wiring connected was the problem point and it needed to be reconnected. I fiddled with the wires again and found that I lost my neutral light, which was interesting. I also made new connector ends for the main ignition switch in case it was a bad connection, but I did not notice any differences besides a snugger fit.

Anyways, my main questions are:
A: Is the wiring in the magneto bad and will it need to be redone?
B: Are there any other spots that could be the issue that I haven't thought of?
C: Why would the taillight be able to power itself from the battery?
D: Could the main switch be causing any issues if it is touchy?

I know that some of these questions will need to have actions performed myself in order to be answered, but I figured I would ask them anyway to see if there's anything that I haven't thought of as being the problem or if anyone else had similar issues when wiring up their bikes. I really appreciate any replies and will keep providing updates as I work through the issue so that it could be used as a reference for others should they run into any similar issues.

Thanks!!!
11 Jan 2022 14:33 #1

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I will reply more later… just a quick question… is this a US model?
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
11 Jan 2022 16:44 #2

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Thanks for the reply! I believe it is a US model... I bought it in Oregon, but I don't exactly know where it is from prior to that.
Last edit: 11 Jan 2022 16:48 by Zyamaha.
11 Jan 2022 16:48 #3

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Okay...  US models starting in about 1970 were required to have the taillight powered from the battery.  I see the wiring diagram doesn't reflect that.  How many wires do you have to the ignition switch and what are their colors?

 
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
11 Jan 2022 18:06 #4

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That's really good to know! So, I guess that part is working properly then. I've got 10 wires going to the ignition switch. The colors in the 6-Pin connector are: Blue/White, Brown, Black/White, Yellow, Green, and Green/Red. The colors in the 4-Pin connector are Red, White, Blue, and Black. I've tested all of the connections for the ignition switch using the attached image and found that it was connecting all of the proper points.

I did find that when I put the switch in place, it was being pulled on a bit when turning. I changed the location and had the wires go through the top of the frame instead of the bottom, which seemed to relieve the stress that was being placed on the wires.

I took off the rubber covering for the ignition switch and inspected the points to see if there was anything obvious. After being attacked by a spider that was hiding in it, I cleaned out the webs inside and found that all of the points look good. This makes me think that the issue could be on the other side of the switch where it may be corroded or something. Not sure how to take it apart without ruining it though.

From my understanding, the Blue/White wire on the ignition switch is what directs power to the headlights and taillight. The taillight shuts off if I tug at the wires on the ignition switch, but it confuses me how it would be getting power at all when the headlight gets none of it. Are the taillight and the headlight both powered through that Blue/White wire or is the taillight powered by a separate wire? (I now know that the taillight is powered by the battery and also the magneto, so I'm referring to when the magneto powers it on for whether they both use the Blue/White wire)

Thanks for your help! I really appreciate it.

 
Last edit: 12 Jan 2022 09:36 by Zyamaha.
12 Jan 2022 09:32 #5

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Replied by Sneezles61 on topic 1972 Yamaha LT2 - Restoring the Original Wiring

Try some contact cleaner... Be careful, it could harm the painted surface... Spay into the key slot.. put in the key and turn it... repeat.. 
It may help to do this with the key in a horizontal position.. This stuff works well with alot of low voltage electrical contact stuff.. 
Sneezles61
12 Jan 2022 11:19 #6

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  • Zyamaha
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Great idea! I'm pretty sure I have some of that lying around in my shop, so I'll give it a shot tonight. I'll let you know if it solved the problem. I appreciate the help!
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12 Jan 2022 11:31 #7

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Blue/white means you have battery powered taillight as expected… wiring diagrams are wrong. I will answer more tonight. 
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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12 Jan 2022 11:42 #8

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Okay so what you can do is look at a CT2 diagram and it will be better than what you have...

The big difference is that Blue connects to Red with key in "lights on" position.  Red comes from battery (DC power) which is why taillight works off battery.  This is how a US model should be wired...  unless they had some sort of exception for a smaller displacement bike I never heard of the tail has to stay on with engine off after about 1970 to be street legal. 

Yellow is AC power directly from engine.  It connects to the blue/white with key in "lights on" position.  Blue/White powers the headlight switch on the handlebar and the gauge illumination light in the speedo.  Again, this is AC, not DC and engine must be running to get power to the headlight and gauge lights. 

LED might not like being fed AC...  and the systems have lighting load "balanced" against output to keep voltage in check.  If the headlight blows or isn't connect voltage can spike and other bulbs can blow.  You can add an AC regulator to keep from blowing bulbs...  service bulletin is in Tech Library or DEET sells one from a scooter that also works. 

Hope this helps...  again, look at CT2 diagram and it might make more sense.
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
12 Jan 2022 19:05 #9

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Also you could post pictures of your switch but most are very easy to take apart and clean.  Check for wires broken off back of switch as that happens sometimes too. 
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
12 Jan 2022 19:07 #10

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