jjdiesel1990

Does anybody have a picture of the infamous 4 prong tach plug on the 92-93 trucks? I got a skinny 4 prong plug down by the brake release, but don't know what it is.

jjdiesel1990

hmmmmmmmm...

rbrettctd

nonintercooled trucks dont have it.

stwcowboy

I bought a tach from O'Reilly's on Saturday and put it in. I located the factory plug under the dash, and wired the tach in per the instructions, but it doesn't work. I have the backlight and keyed 12V. The input source (I'm assuming this is coming off the Crank Sensor) is getting voltage that changes as the RPM of the engine changes, but there is no movement of the needle on the tach. I'm going to try and call the tech support line, but I was wondering if anyone else has had this problem.

gomerpile

well the tach you installed might be a sunpro like mine you might want to check you have it in the 4 cyl mode. and make sure you got the ingnition plugged up, check all connections. and also over at thedieselgarage i heard that some wont work because the pcm doesnt put off as much voltage as required.

bigragu

Isspro has the harness made to attach onto the zOEM tach provision socket. And, unless I'm mistaken, the harness, unfortunately, works with their tach only.

stwcowboy

I had my switch in the 6 cyl mode. Should it really be in the 4 cyl mode??? I called the company and they said that tach wouldn't work on a diesel, and they didn't make one that did. Back to the drawing board. Thanks for all your help.

wannadiesel

Yes, the PCM sends out 2 pulses per revolution.

dpuckett

Get an ISSPRO from Geno's Garage, PDR, et al, and be done with it. You will need the install kit for the 89-91 trucks.