1988 Chevrolet Truck • 21,700 miles

Grandsons truck has no speedometer or milage movement on his dash. Trans tail assembly has the sensor/fitting for the cable assm. His wire harness for the sensor plug is the pulse type. Looking up in the dash area I can not find the plug in for the cable assembly. Getting back to the tail assembly can I get a short tail transmission assembly/with the pulse sensor in it and will it work?I am stuck on what I can change and not change.I went to a local pull-a-part and got the pulse sensor and plugged it in nothing works yet.
May 13, 2012.

1988 is a little old for it to be a pulse sender. You would be able to and would have to find the connector on the wiring harness which would be hanging near or around the transmission tail. Otherwise it has to be a cable and if it has a cable fitting thaat is what it is for. An electronic fitting near it on the tail would be a sensor for load on the engine and transmission shifting.
So, you can't change them out as the wiriing has to be there and if it is not hanging from the harness, it probably is just lost. It goes throught the firewall into the interior rear of the gauges.

Ok doing some homework and will replace the original tail assembly speedo driven gear thing. Have a cable coming to fit on the tail to the cluster with the pin. I see no(hole) thru the firewall to go to the transmission rear. Do I drill thru the firewall. Another thing I can not find the hole in the back of the cluster to insert the pin-type cable into. Is it easier to disassemble the cluster to locate the pin area? Thank you, kenny

May 15, 2012.
It will probably help you find the speedometer cable and its route through the firewall, it has to go through the body of the cab somewhere, by removing the instrument cluster first.
I am giving you an exploded diagram of the instrument cluster, it does not show cable hookup but may come in handy. I also am giving you an exterior diagram of the transmission showing parts #30&31, in top right box, as the speed sensor and the speedometer cable drive.
The service manual I have is somewhat ambigusous as the same tranmission is in the "S" series and is cable, but the "K" series alludes to the cable running from the tranmission to posssibly a hookup outside the cab that converts the signal there and sends an electronic signal to the instruments. I am really not sure about that as the wording in the service manual we sue can be very mis-leading. I just wanted to give you the information as I could best translate it. Without supporting diagrams showing the entire path of the speedometer cable I really cannot give you a definitive answer. I think between the diagrams AI am giving you and information, it should be easy to figure out how the setup works with the truck in front of you.
Let me know if there is anything else you need.

I now have to wait for the cable ordered from J.C. Whitney Co. My grandson is using the truck so probably this weekend I will start to tear the cluster apart and see what is what. Thank you DrCranknWrench for your info and input. Will post what I did and found.

May 15, 2012.
Your very welcome.

I would appreciate the outcome as I always like to know if a customer is taken care of or not. Not only that but mechanics is a constant learning experience and I never pass up the opportunity for more information.

Take care and good luck.