Airhead Tach not working...

[browncycle]

I have a 1982 R100 that started life as an RT and the tachometer has never worked. It is electric.

Anybody have some suggestions on how to fix it, or at least make it work.

It has already made a trip to the speedo repair shop and and came back with a clean bill of health. It must be in the wire or at the source. I think.

Any help would be appreciated.

Thanks.

[boxerboy81]

Do you know if it works in another bike? If so, it's a problem somewhere else.

Have you tried another tacho in it's place? If it works, then it's your tacho not working. If it doesn't it a problem somewhere else.

Clean all connections from the coils and ICU maybe?

[browncycle]

Thanks. As I said, it came back from the gauge shop with a clean bill of health, "even when violently shaken." that's really what they said.

I was hoping someone had run across this and solved it. And then impart to me that knowledge.

[Grider Pirate]

I don't have a wiring diagram handy for the bikes with an electric tach, but I would bet money there are three wires that go to it. 1) +12v, 2) Ground, and 3) signal. The signal wire will go to somewhere in the ignition circuit. Sorry I can't be of much more help. I did (just now) look at a Clymer manual, and it is of little or no help. I have used a variety of tachometers on BMW's, and all the Japanese tachs (that I've tried) just take the signal from one of the connections on the primary side of the coil.

[boxerboy81]

Yeah, good point...maybe those wires aren't in the correct spots? There are three wires, at least on the earlier electronic tacho. Maybe the circuit board is the problem?

[batoutoflahonda]

here is a link to a wire diagram. maybe it will help.

http://www.bmwr65.org/cgi-bin/yabb2/...num=1276724607

[Wirespokes]

I'd suspect either the connection at the large black plug to the instruments, or the light board inside the instrument housing. It's not uncommon to find 20 ohms and up between the light board pins and copper traces.

And the large bundle of wires hanging underneath the steering head that terminates in the large black instruments plug takes a bit of abuse down there - it's quite possible a wire has broken, especially if the sheath is compromised.

[boxerboy81]

The three wires on the left, to the tacho...are yours like that? otherwise, I'm also thinking a wire in the harness, though if one is gone, there may be more and other symptoms???