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1971 DT1 electrical issues

  • mskobin
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1971 DT1 electrical issues was created by mskobin

Hi All

I've been restoring a 1971 DT1 and I can't figure out what went wrong with the electrical. When I got the bike, most of the lights and electrical components had been disconnected and I've been trying to figure out which wires go to what component. Specifically, the brake light, turn signals, and horn were working for a while and then all of a sudden they weren't... I then found a couple black wires that were still taped up, so I'm guessing those components weren't properly grounded and maybe I blew a fuse? I can see a fuse on the wiring diagram, but also can't seem to find it on the bike.

Any suggestions?

Thanks!
The following user(s) Liked this Post: Sneezles61
27 Jul 2021 08:43 #1

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Replied by Sneezles61 on topic 1971 DT1 electrical issues

Nows a good time to remove the fuel tank and look at ALL connections.... Corrosion happens and contacts loose their connection... My fuse was under the seat, back fender with a big rubber boot over it...
Sneezles61
27 Jul 2021 08:51 #2

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Replied by msavitt on topic 1971 DT1 electrical issues

Hi There -

I am not an expert, but got the same bike and recently got everything working so I will share what I know.  Perhaps good news, the brake light, turn signal, horn and tail light all run on DC from battery, so you might have a single issue knocking them all out.

Before you do anything you should get the electrical schematic off the tech library as it shows not only wiring layout, but also the switch logic for the 3 position switch too.  I would disconnect the large plug at the end of the switch and test the logic at the various positions to eliminate the switch because IMO its the most complicated part aside from the lighting coils which mystified me.

There is, or should be, a fuse between the battery and the harness, so assuming your harness is intact - meaning not hacked up - you should check the fuse and the voltage of the battery by putting a 6V bulb or horn across it.  If battery and fuse are good, then check the red going into the harness from the fuse.  It splits with one side going to the rectifier and the other to the switch. You should check for 6V at the end of both. 

Does bike run?  If bike runs, then headlight and gauge bulbs should light assuming they arent toast when engine is running and switch is in position 3, which is night mode.  If yes and yes, then I would look for 8 to 9 volts across battery with engine running and engine reved up that would indicate that the battery is charging.

If all of this is good, then its time to get the VOM out and check grounds, connections, etc. until you find issue.  It looks and is complicated, but I simplified it in my simple mind by breaking things down into three separate sub-systems - 1. ignition, 2. DC stuff, 3 AC stuff and charging.

I hope this helps, you will def get this all fixed!

good luck
Martin

 
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27 Jul 2021 09:07 #3

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Replied by mskobin on topic 1971 DT1 electrical issues

I appreciate your replies!

I took this bike down to the frame when I was restoring it and have been referring to original photos to see if there was a fuse, but I don't think there was. I'm planning on walking through the wiring diagram and testing continuity between specific components to try and narrow down the issue. The bike starts/runs great, and the headlight does come on when it's running, so I think it's just something in the DC part of the wiring.
27 Jul 2021 10:05 #4

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Replied by Pedalcrazy on topic 1971 DT1 electrical issues

I’ve restored a few now and no longer fear not remembering what wires go to where. Yamaha made the wiring connections so like colors plug into like colors at the connecting points on the bike. On the 71 you’ll have an extra white wire out of the magneto harness that stays under the tank and an extra black wire also out of the magneto that nothing plugs into located about mid-magneto harness. All other wires plug into the same color of wire with no leftover connectors on the bike (unless you don’t have turn signals—then you’ll have two brown and two green leftover).  Keep that in mind if you get stumped or confused.
1978 DT400E
1976 DT400C
1973 RT3
1971 RT1B
1968 DT1 (3)
Last edit: 27 Jul 2021 16:07 by Pedalcrazy.
27 Jul 2021 16:02 #5

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Replied by msavitt on topic 1971 DT1 electrical issues

that extra white wire with a Y connection to green and green/red came in handy when my green wire was putting out nothing!
27 Jul 2021 17:30 #6

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Replied by mskobin on topic 1971 DT1 electrical issues

Thank you everyone for the help! I was able to locate the fuse (also upgraded it to a blade style fuse), and spent 2+ hours diagnosing continuity between wires. Turns out the aftermarket horn I put on has a nut on the back that was barely touching the frame and short-circuiting everything... I feel so dumb, but also so relieved it wasn't anything more time consuming to fix.
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28 Jul 2021 10:27 #7

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Replied by Gr8uncleal on topic 1971 DT1 electrical issues

No need to feel dumb - good detective work and it signposts to other forum members a potential issue to be aware of. 

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28 Jul 2021 10:52 #8

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Replied by noteforjim@gmail.com on topic 1971 DT1 electrical issues

Martin,
Do you have the wiring diagram for a 1971 DT1E? I dont see it on the tech library. Any help would be greatly appreciated.

Thank you
15 Sep 2023 09:46 #9

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Replied by RT325 on topic 1971 DT1 electrical issues

Page 105, bottom page. Manual says "69-"71 so must be the same i guess.
www.yamaha-enduros.com/index.php/service...ctory-service-manual
So going on the theory that nothing change up to "71, here's a color diagram.
www.yamaha-enduros.com/index.php/wiring-...color-wiring-diagram
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15 Sep 2023 20:58 #10

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