After market tach connection

[audijunky]

Allright I have hooked the tach up to one of the negative leads from the coils. The tach jumps around alot up until what it is reading at 3.5 K rpms. After that it is smooth . Any ideas why it is acting this way?

[Pat Kelly]

Do you have the + comming from the coil and the - going to the TCI box (in line)? Or the + 'Tee'd' to the coil wire and the - going to a direct ground (in parallel)?
At about 3500 rpm the voltage reg diverts the charge to ground (if this effects anything in this case). Just mentioning it because that's something that happens around the same RPM.

[audijunky]

No the way it is supposed to work is of the signal to the coil. since our bikes have two, I used oone of the negative leads from the coil as a + lead to the tach, through the tach and then to ground. So when the coil fires it also sends the voltage/signal after the coil to the tach and then to ground so as not to drain any of the voltage before it gets to the coil. So to answer your question now that I have read it again, I have the negative going to the tci Teed and the grounds in parallel.

[randy]

Steve,

Your tach needs 12vdc for the internal electronics. i think what you're seeing jump around is the 8-11 volt swing of the TCI because you're trying to use that lead as the power lead for your tach.


In your original post you wrote that you have four leads, two for power (red/black)? Connect those to battery and ground respectively.

The other two were one for coil, connect that to TCI side of coil, and one for ground, ground it. That should get you working and light the light.

[audijunky]

Hey randy that makes sense, I forgot to mention that the backlight for the tack was not illuminating. Must have it connected wrong. I am trying to use the wires that were going to the old tach so that it can be switched. I thought I connected to the correct ones, I will have to check again obviously.
Gracias my Guru friend

[randy]

Steve,

Inside the tach shell, the brown is +12v, black is ground

[audijunky]

Hey Randy,
I used the clymers diagram but its kinda hard to make out which one to use. I dont know right now which one i used. Does the brown have voltage only after bike is started or when the key is first turned on?

[LoserShoes]

Brown -- switched on with key.

Only thing that is operated with the engine start relay is the headlight.

Steve

[John]

Actually

The headlight has it's own relay that is energized by the alternator. Other than the starter being controlled by the start relay, the only other item recieving voltage from the start relay would be the ballast resistor, in the cranking mode. The headlight won't come on until the alternator is working.

[LoserShoes]

OK maybe I should have said "Engine Started" relay??

Steve