Early Dodge Cummins Tach.

[Mark Nixon]

I may well have solved a question that has been posed numerous times:
"What are the extra plugs near the column on the '89-'91 diesel trucks for?"

I was gallivanting the countryside chasing down some leads on trucks I found on Craigslist and stopped in to pick up an NV4500 transmission core that was reportedly in a "1993" 1 ton.
I get there and see it has this tach on the dash, so I 'm pretty much figuring it's a '92-'93 truck, right?
WRONG!
Got to looking and it has the grid timer under the column, the remains of the shroud also confirm it's pre-intercooled.
A glance at the registration that match the VIN on the dash and the tag on the hood confirmed my suspicion that it indeed a '91 Non-Intercooled truck.
Then it dawns on me what I just found.
A quick check finds the crank sensor wiring harness coming through the firewall with a definitely "Not Chrysler" wiring plug.

We pull the tranny, make a deal on the tach (The sensor was still on the engine, got it, too).

Turns out, it looks like even the wiring on the older trucks acknowledged the intent of a Chrysler supported tachometer as a dealer installed option, as the '92-'93 trucks do.

I'll have pics of this up in the next day or so, as well as 100% verification that the plugs are present on other /89-'91 trucks and that this event wasn't just a fluke.
I doubt that it was.

Mark.

[BobS]

Here's a few pictures & explanations that I posted earlier over on DTR for a 1989 Dodge Cummins truck with a factory tach installed:
FWIW, here are a few pictures of the factory supplied tach wiring harness used in the 1989 Dodge that I have and there is not a PCM installed on the fender. Under the dash there is what looks like an intermediate adapter cable between the under hood tach cable and the cable that leads to the tach head. I believe it may be there to pick up voltage from the 1989 wiring harness to the tach head and probably not much more. Too wet outside to continue any further.

The tach wire comes through the grommet in the firewall (bottom right corner) and into the back side of the plug at the center right in the picture. EDIT: The opposite end of this plug which is facing you is the tach connection. I had assumed this was where the power switched leads were but instead they are attached to the same side where the sensor is connected. Those power switched leads are the red- orange- and black.


EDIT: The red orange & black power leads are fed from the connector plug shown in the center of this picture. The tach leads are just to the right coming out of what looks like a piece of plastic tubing and drop out of view in the lower right corner of the picture. RED-white-orange- gray:


There is no PCM in this truck. NOTE ALSO the sensor has 2 wires running to the harness:

[Mark Nixon]

Bob, Thanks!
You saved me extra time chasing wiring and uploading pics!
Everything I'm seeing says these tachs were NEVER factory installed, just dealer or owner installed.
ALL of the "factory" ones have "JAPAN" molded into them,too.


Case in point, if they were ever FACTORY installed, they'd be called out on the build sticker on the hood, as they "would" be considered a special order.
I have yet to see a hood sticker that calls the tach and I have seen numerous 1992 and 1993 trucks with them, even have one in the yard that has one in it, no info on the build sticker.

Mark.

[Erska]

More info and pics please! where I can get a tach? to the dash?