• Hello Guest, welcome to the initial stages of our new platform!
    You can find some additional information about where we are in the process of migrating the board and setting up our new software here

    Thank you for being a part of our community!

Tach issue

1

1978MY

New member
Joined
May 24, 2018
1985 245

I’m replacing my Large clock with a Tach.

Issue: car won’t start with the Tach plugged or would die if I plug it while running. Looks like I think the Coil gets grounded and kills the spark.
HTML:

So far:

*Got the Tach tested and tested shop said no issues there.
*Tried the Tach in 2 different clusters
*Ran a new temporary Tach signal wire from the coil to trouble shoot the wire.

What else can I try to figure out what’s wrong?!
 
Using a small clock as well? Maybe try it without the clock connected. The harness on the clocks sometimes likes to short itself out, causing lots of weird issues.

-J
 
Where are you plugging in the coil wire on the tach? The top 3 spades are for the small clock harness, the bottom 2 spades are coil wire for tach (use either one, they're connected together within the tach).
 
Tried both spades.

Tied another thing.

Plugging the Tach to the other side on the Coil marked 15. The car started, Ran, no reaction from the Tach But the car wouldn’t turn off when I took the Key out.
Turned off when I unplugged the Tach.
 
Sounds like electrical power is backfeeding through the cluster to the ignition system when the tach is connected. Kinda like when the tailgate harnesses are shot and the headlamps are turned on. Causes the ignition system and fuel system to receive power, along with all the warning lights, gauge, etc.

-J
 
John242Ti said:
Sounds like electrical power is backfeeding through the cluster to the ignition system when the tach is connected. Kinda like when the tailgate harnesses are shot and the headlamps are turned on. Causes the ignition system and fuel system to receive power, along with all the warning lights, gauge, etc.

-J
Click to expand...

But it happened with 2 Clusters. So where would the issue be? Any idea how to solve this issue?
 
It sure sounds like the tach is drawing too much power and killing the spark. Normally, the tach is a very small electrical load compared to the several amps of current needed to charge the coil. You could try powering the tach or console out of the car and then connecting to the coil. You'll need to find +12volts and Ground on the tach/console, and then the coil wire is obvious. If the car idles until you connect the tach wire, it must be the tach (or at least I can't think of anything else).

You could also try cleaning up the ignition module to coil connectors. Maybe the extra load of the tach pushes it over the edge, but the tach really should be insignificant compared to the charging current.

Have you noticed if the tach moves at all before it kills the engine?
 
RonJ said:
Just to verify, Tach is connected to the - (negative) terminal on the coil.

RonJ
Click to expand...

It is. I even tried connecting it to the positive. Car ran Tach didn?t react, car wouldn?t turn off till I unplug it 🤷*♂️
 
You must log in or register to reply here.
Back
Top