R12 wiring HELP!

[Bruce Frey]

Here are some things to think about as you wire your bike.

If you look at the schematic in the Bosch manual, there is just a single wire from 51 on the mag to 30/51 on the board. Some harnesses I have seen have another wire from +battery to 30/51 on the board.

The Bosch JN5 tail light should have both hot and ground wires as the schematic shows. The ground wire is used instead grounding to the frame (like the horn) because the JN5 was also designed to be de-mounted and used as a hand light. If you have a later JN7 which is not de-mountable, you could probably ground to the fender and omit that wire.

If you have a brake light, I would take power from the tail light (58) terminal.

Make sure -battery is well grounded to the frame. I also like to have a dedicated ground wire from - battery to the 31 terminal on the board as well as a ground connection from board 31 to the headlight shell (otherwise headlight may depend on a ground connection through the headset bearings).

Good luck!

Bruce

[Bigsieuk]

I've run wires as per the Bosch manual back to the board and labelled as you suggested. I've also been studying the 'original board' pictures that were on the ebay site (thanks for those whoever you are).

I've overlayed the switchable connector at the end of the key barrel onto the ebay pictures to indicate which points are connected when the key is turned, I'll then overlay that onto the new board I've bought to see which connectors align correctly and run the new wires accordingly. If I had the skill set I'd manufacture the boards up as per the ebay picture. Might make things easier for mag R12 owners.

I've found this a great help and I'll post these up when I've completed this exercise.

Regards

John

[Bruce Frey]

As I re-read what I wrote, I should have said to make sure -battery is well grounded to the frame AND THE ENGINE/TRANSMISSION. I run a wire from -battery to a transmission bolt.

The - terminal of the generator is its frame. If you need to shim it to adjust chain tension, you must use metal shims to maintain continuity to the engine case.

Bruce

[Bigsieuk]

Thanks Bruce and Darryl,

I went back to basics on the wiring and ignition.

I put the new loom back in the box and ran my own wires as there are so few. With the board again I went back to basics, I disconnected all the wires that come with the loom and overlaid the (what I believe to be) original layout for the wires. and connected accordingly. I ran an earth from the tail light back to the board and connected it to the earth from the battery/frame/gearbox just in case.

The only issue I can see is that you can remove the key from a non-central position and leave live power to the lights accidentally you could run the battery down.

As often is the case there was a lot of fettling to get things to fit properly. It may have been easier if a mag R12 specific board were available but I can understand the reasons for manufacturing a 'catch all' board and loom.

Regards,

John

[Darryl.Richman]

Congrats, John! That's what I do on these bikes because, as you say, there are so few wires to run. Now you know just how it's all wired and it won't ever be intimidating to you again.