My custom tach won’t work

[832.3ranger]

I took a 1988 2.9 cluster out of a 1988 extended cab 4wd xlt ranger. And then took a tach out of a 2.3 mustang and put it in my housing and then connected the leads to have a 2.3 tach in my truck. It worked for about 4 or so months then it turns on and stays at 2800-3500 rpm and I’m wondering what I did wrong to make it stop working or is it just because it’s old. Thank you in advance.

 

[franklin2]

Take the signal wire off going to the coil. If it still reads more than zero rpm when you power it up, it's broke.

 

[832.3ranger]

Take the signal wire off going to the coil. If it still reads more than zero rpm when you power it up, it's broke.

Okay thank you. Is there any way to fix it? Or is it a total loss?

 

[franklin2]

Okay thank you. Is there any way to fix it? Or is it a total loss?

Try the take it apart and put it back together trick. That fixes a lot of stuff for me. You can't hurt it anymore than it is if it does turn out broken.

If you want to bench test it, put the ground and power to a battery charger, and then take the signal wire, and brush it against the ground. As you brush the signal wire on the ground, it will give you a poor intermittent connection and that is enough to make the tach needle jump. That is all it does, is reads a signal to ground, that is how the coil works. The ignition system grounds the coil and then takes it off ground and that makes spark at the coil. The tach reads this signal to ground.

 

[832.3ranger]

Try the take it apart and put it back together trick. That fixes a lot of stuff for me. You can't hurt it anymore than it is if it does turn out broken.

If you want to bench test it, put the ground and power to a battery charger, and then take the signal wire, and brush it against the ground. As you brush the signal wire on the ground, it will give you a poor intermittent connection and that is enough to make the tach needle jump. That is all it does, is reads a signal to ground, that is how the coil works. The ignition system grounds the coil and then takes it off ground and that makes spark at the coil. The tach reads this signal to ground.

Thank you, I’ll try that when i have a chance to tear it apart. Unfortunately it’s my daily so i can’t afford to have it torn apart for a long time.