On the back of my 1990 t-case right next to the speedometer cable is a electrical connector. What's this for? Thanks.

 

If it's the one that plugs into the cable housing right at the transmission, that is the vehicle speed sensor for the computer. Later trucks moved it to the differential.

 

Yes it plugs in right next to the speedometer cable at the rear of the t case. Reason I ask is I R&R the tcase and now I have a rear abs light on. Any ideas on what I did to cause this?

 

I believe if that sensor is not working properly, it will indeed cause RABS light on that generation of truck. Might want to make sure you didn't damage the sensor or the wires.

 

The RABS sensor is bolted on top of the rear differential housing and sends
a signal to the ABS control module when the rear wheels are moving.

The unit connected to the speedometer cable as mentioned is the VSS and
used for cruise control.

So your work on the transfer case shouldn't cause a problem with the ABS.
Did you unplug any electrical connectors along the frame rail?

 

Thanks for the help. I only R&R the tcase while changing a clutch and swapping a 4sp to a 5sp trans. Cruise control is working fine. I traced the wires from the rabs sensor on the rear diff along the frame rail and saw where I had disconnected it apparently. Swap went fine and now have a low mileage trans behind the 300 six with 255000 miles. Best truck I've ever owned and that includes a few dodge cummins which also are great but very expensive when anything goes south.

 

Can you provide some info. about your swap?

You went from a T18 to a Mazda M5R2?
Did you have to cut a new hole location for the shifter?
What transfer case was used in your 90 1345 or 1356?
Did your drive shaft length change?
Was the rear transmission mount the same?
Was the transmission support cross member the same?

Thanks.