Tach jumping around after RPM Window Switch install
 

I installed Jegs RPM window switch #40824

This is a digital window switch that also displays RPM.

I used the white tach wire from the pcm and set the switch to 4cyl mode

The tach jumps around like crazy. The Window Switch displays the correct RPM.

I can switch it to 8cyl mode and the tach performs as desired, but the window swich shows half of the correct RPM.

I tried boosting the tach signal as suggested in a search with a 1k Ohm resister to 12v+, but this made no difference.

Any suggestions?

Tach signal
 

What kind of vehicle is this?

Are you saying if you change the RPM switch setting from 4 cylinder to 8 cylinder that fixes the problem with tachometer?

get rpm from a coilpack wire and not the tach signal. its the light green wire

The tach wire is only a couple strands if you used a tap-in style connector it cut the wires.You now do not have a good feed. solder the wires with a good conector and it will fix your issue.

We always pull signal from a coil or an injector.

-Garrett

1998 LS1 Camaro

Yes, it fixes the problem with the tach, but then the rpm window switch reads the wrong.

Any coil? just 1?

I solder and heat shrink every connection.

Ok, I will search how to do that.

What do I then set my Window Switch to? 4cyl still?

The harness where the entire bank of coils plugs into the main harness. Pull from the main harness side, light green wire. Keep it set to 4cyl, since you're pulling spark from one bank.

I was told by Jegs that I need to buy MSD Tach Driver
PN 8913 for it to work.

Thanks for the info.