Tach

[Lenard]

ok i know i'm asking a lot a of questions here, but i'm young and don't anything... :oops: anyway trying to hook a tach up in my truck it's mounted and wired up and has power but isn't showing anything, we only found one wire that came from the coil on the inside of the firewall. hooked it to that but as i said, nothing, then we thought maybe there was break in that wire somewhere so we got a long piece of wire and hooked it direct but still nothing. any idea's??

[Eagle]

Okay, it's an '86 2.5L so that means it has the same coil pack and ignition (RENIX) as the 4.0L models from 87 thru 90. First off, are you wiring a factory tach, or aftermarket? A factory tach should work when plugged in, there shouldn't need to be any wiring.

 

So, assuming it's aftermarket, the instructions for the Sun Supertach I put in my '88 said to connect the black wire to ground (duh!), the red wire to battery voltage (preferebly a fuse that's switched by the ignition), and the green wire to the NEGATIVE terminal on the coil.

 

Perhaps you are connected to the wrong side of the coil?

[Joe Jeep]

I put an aftermarket tach on my '87 2.5L and connected the signal line from the tach to the tach line in the wiring harness. I think it was under the black cover on the passenger side of the engine compartment.

[Renegade]

Man I love this website. Found an old aftermarket tach today & want to put it in the MJ. Had an idea which wire was which but wanted to be sure so I was gonna post up to ask, when VIOLA! here it already is :D

 

I got a blue wire as well. I assume that would be for the light in the tach.....

[Lenard]

Got it!! We looked closer at the book and there was 2 wires coming through the firewall that was green w/ white stripe, well apparently somebody switched wire colors so we run a new wire and got here going. I got it on the HWY to see what she was running at 70mph, 3400rpms, does that sound right? 68mph and under the truck runs smooth, but 70 and over it vibrates to bad, may have something to do with mud tires 8)

[Eagle]

I got it on the HWY to see what she was running at 70mph, 3400rpms, does that sound right?

Yup, that sounds right on the money for a 4-speed.

[Lenard]

now i got another problem, whenever i hit the horn the needle goes down between the 1 and the 0 and just flops around, and it takes it all night just sitting there before it will quit doing that. whats the deal?