Heavy85

It's an '02 Z28 engine/PCM. I have the white wire from the interior connector tied to the Autometer tach signal wire. Based on searching here I added a pull-up resistor starting at 6xx ohms then trying 480 ohms based on a couple of threads. I get nothing - no needle movement. I know I'm getting power and ground as the gauge light comes on and the power/light are spliced together. I put a voltmeter on the white wire and I also get nothing. Also based on a post here I was expecting ~9V (realize it's a frequency so it's average voltage) but I'm getting no voltage. Is there some fuse or other input to the PCM that needs to be hooked up for it to output a signal to the tach that maybe I'm missing? Any other thoughts? I'm using the f-body wiring harness. Yes I cut both orange and brown wires on the tach (older one before they went to the switches) to make it a 4 cyl.

Thanks
Cameron

Heavy85

Nobody??

ghettocruiser

iTrader: (17)

Ok... It sounds like you are short cutting on your wiring. Splicing guage power and the light wires together??? Just not good practice. Keep your light on its own power/ground source. Then bring a GOOD switched 12volt wire to the tach and a GOOD chassis ground.

Thats all you should need. Assuming your engine wiring is good, you should get a tach signal and tach movement no matter what the tach is set on. Even if it wasnt set on 4cyl, it would still read. Just wrong.

I wouldnt expect to get voltage at the white #10 wire for the tach signal. But Im not an electronic genius...so maybe it does produce voltage. Are you sure the white wire you are connected to is a) the correct white wire, b) has good continuity and not broken, and c) is actually coming from the PCM, and not some other part of the harness that might not be connected to the PCM anymore. Gauges can be finicky with their power/grounds, and sometimes dont like to share those connections with other circuits.

When I set my full gauge set up, I ran each gauge to a small fuse block, each on its own 3amp fuse per Autometer's recommendation. I spent a lot of money on them and wanted them protected. I DID splice the grounds together. But I used a BIGGER main ground wire, and soldered the smaller gauge grounds to it. Its alittle extra work...but its more organized, more protected, and usually works when its done.

J.

Rodder

iTrader: (2)

Interior connector? The TACH signal is on the white wire of C105, the 8-pin black under-hood metripack connector, terminal G. it is a white wire though. I'm using a 99 harness/PCM and didn't have to do anything special to use my AutoMeter UltraLiteII tach with it.

Heavy85

Yeah I'm a putz. Had the wrong white wire. For some reason I had it in my head that it was the white wire on the blue (I think) connector just after the harness comes inside the firewall. It's weird that terminal G doesn't actually go anywhere on the f-body harness it just stops at the black connector. Anyway tach works now.

Thanks
Cameron

Rodder

iTrader: (2)

as far as simple mistakes go, at least that one was pretty harmless!

jannes_z-28

Did the same mistake...

https://ls1tech.com/forums/conversions-swaps/784870-solved-stupid-tachproblem.html


Jan