New Tachometer Installation

[Jrg303]

Hey Guys,

I’ve got a ‘79 F100 with the L6 Electronic Ignition system. I recently bought a cheap, Amazon tachometer for it. I installed it per the instructions: 1) red to the ignition switch via the fuse box 2) black grounded to the dash via a self tapping screw 3) green connected to the “tach output” side of the coil via wrapping the wire around the post.

However, when I cranked it, the tach read 9500 rpms at idle.

What did I do wrong? Is it just a cheap tach?

[cep62]

there's settings for 4 ,6 ,and 8 cyl.

[Jrg303]

Yep. I switched it to 8 cylinder, but that didn’t fix the problem.

When I tried switching it to 6 and 4 cylinders, it stayed pegged at 9999.

[cep62]

I D K
double check the ground screw with a test light to make sure it's a good ground
maybe it's a defective tach ?

[Jrg303]

That’s what I thought as well, but I tried another tach and had the same issue.

I thought about the ground screw, but it’s connected to a self-tapping screw drilled directly into the metal dash. I’ll check it today and see.

I also thought that maybe I just hooked it up to the wrong output on the coil, but it’s labeled “tach test”.

I’m stumped.

[zgerbic]

Checking grounds is very good advice.

The signal at the tach test pin might not be the signal you are expecting if the truck has electronic ignition, especially if it is a multispark system. I suspect the tach will work if you hook it up to an older 60's truck with points or a Pertronics type ignition. Temporarily hook it to some older vehicle, if you can, and see if it works. If so hunt a tach compatible with the electronic ignition on the truck, or perhaps get a converter to drive the tach.

[basketcase0302]

Test a 12 volt fuse using the same dash metal to see if you can read voltage there.

[Jrg303]

I bought a (more expensive) Bosch tach that was compatible with the electronic ignition. It worked like a charm!

Thank you for everyone’s help, especially zgerbic! I really appreciate it!

[Raiver]

I bought a (more expensive) Bosch tach that was compatible with the electronic ignition. It worked like a charm!

Thank you for everyone’s help, especially zgerbic! I really appreciate it!

Okay, I will tip my friend about getting a legit tachometer for his new T100 project. The current one is probably a cheapo one as the reading fluctuates on idle. We'll check it when it returns from the installation of the new tires from 4Wheelonline.