What's my goof? No speedometer in S10.

Hi Bob,
Congratulations on your first drive! I remember I was missing the dashboard, hood, license plate (oops!) and a few other items for my first test run down the street. You were wise not to cut anything. I did the same, leaving a huge wire harness on the fender until the time came to finally be brave and remove all the unneeded wires and plugs.

My S-10 is a 1994, which I believe is the first year GM started using an electro-mechanical speedometer in the S-10. Prior years used a mechanical cable linking the transmission to the speedometer.

On my 1994 S-10, the data cable is very easy to spot, as it is the only twisted pair (actually, it's 3 wires if I recall correctly...) data cable I saw on the truck. It's a fine wire cable, similar to an ethernet cable, although with fewer wires. The wire runs from the transmission sensor to a small plastic module mounted on top of the engine computer. Both are located under the dash on the passenger side. From this module, a similar twisted wire goes to the speedometer.

It is my understanding that later model S-10 pickups had the engine computer and the plastic speedometer module combined into a single metal box located on the passenger side fender under the hood. Since I don't have a newer S-10 with this feature, I'm not completely certain of the changes.

Hope this helps, Cornelius

Yes, my '99 has the control box mounted on the right front inner fenderwell.
Is there something I need to do to keep the speedo working?
Bob

Did you pull the transmission at any point? Could be as simple as forgetting to plug the speed sensor back in when you did. *shrug*

Since my S-10 is older, I can't offer a specific suggestion. One thought that comes to mind is that the power or ground needed by the speedometer circuit is connected through one of the many no longer used plugs on the engine wire harness.

If you have a Chilton's or Haynes manual, it may help in tracing the wiring. The best is to use the actual factory manual, but they cost more. The only other thought is don't use a test probe "buzz light" on any of the wires related to the computer module circuit, as these draw too much current. Use a volt ohm meter instead.

Need more info
What year is the S10 and what was the trans/ICE combo?

My S-10 is a 1999, Reg. cab, short bed. It was a standard bed, I took it off (ready to rust through and replaced it with a step-side bed, hinged to expose the eventual location of main battery pack.
I did not remove the transmission, just pulled the ICE, a 2.2l four banger in front of a standard (manual - not automatic) 5 speed transmission.
I did not cut any wires, the only wires unplugged were those on the engine itself as it was pulled from the car. The transmission remained pretty much unmoved/unscathed in the removal process. (I even managed to remove the dreaded engine to transmission bolts with no problem - simple trick - remove the engine mounts completely from the block - things will drop enough to easily access the troublesome bolts with a universal jointed socket on an 18" extension and ratchet wrench.)
I did notice today a couple ground wires not reconnected (they had been bolted to the engine block) - I suspect they might have some effect, but not sure - haven't had any time to work on the truck today.

There are about a big bunch of plugs dangling that were unplugged from the ICE. Only the two grounds, I may ground them out tomorrow and see if that makes a difference. If it activates my speedometer, I will for sure post it here. But as of today, still no speedometer.
Other items I will need to address: there are a few "idiot" lights lit on the dash - "ABS", "Security", "Battery", and a couple others. I suspect I will have to address them one at a time.

I did purchase the Factory Service Manuals - three huge books costing about 90 bucks - WAY too much information.
I also purchased from a web site mentioned elsewhere on this forum the S-10 wiring diagrams for my 1999 truck - still 68 pages!

I did notice today a couple ground wires not reconnected (they had been bolted to the engine block) - I suspect they might have some effect, but not sure - haven't had any time to work on the truck today.

Click to expand...

I think you're on the right track with the grounds. My 97 S-10 conversion had 3 seperate ground leads in the engine compartment. One was toward the right front frame rail near the original battery, another further back on the right frame rail near the rear of the ICE engine, and one was on the left front frame rail near the raidator support. I think all three had multiple wire connections. I wasn't able to get my interior or dash systems working until all three of these were re-attached. I also had to redo the original OEM 12v battery ground lead.

Good luck!