Electrical schematic handy??

[newmaac]

I loaned my 2 manuals to a buddy, and am watching the mailbox for the CD that I recently ordered.
Could someone take a moment and look at an electrical chart for me?
On a 1981 Midnight Special, there is a wire harness coming from the tach. It has several wires, most being for various lights.
Is it the white wire that actually runs the tach itself.
My son is trying to temporarily mount an XS1100 tach in his VW Bug, LOL , and I want to make sure that he is using the right wire, when connecting to the coil.
thanks

[TopCatGr58]

Hey there NewMaac,

According to the diagram in my Clymer's for an 81SH the yellow is the power, the black ground, and the white one goes to the Reg/Rect/Alternator, not to the black CDI box. So I'm not sure if Yamaha set it up to sense the cyclic surges from the alternator vs. pulses from the pickup coils or neg side of the actual coils like what I think most electronic tachs for cars I've worked with did?!

So...not sure if it will work with the VW bug. Might be better off getting a $25.00 tach from auto store that is designed to work with car engine....you might burn up the Bike Tach??

T.C.

[bgomez]

Years ago I tried the reverse. I tried to place an auto tach on a bike. It was not worth the trouble. By the way, you mention a CD. Is this the tech manual? can you tell me where to order it??

[sidecarKev]

CD ordering info.

CD Manuals

Lots of good stuff. Well worth the money.

[tommystinson]

That's pretty interesting about the alternator output being used for the tach signal. I'd love to hear the engineering justification for doing it that way.

[John]

It senses one of the three phases of alternator output. The faster the engine spins, the faster the pulses happen. The tach just shows how fast the pulses happen, and displays it on a scale (meter face) that represents engine rpm (tach). Kinda like a how a timing light works.