TH400 connection issues

[former520]

Hi everyone, I am new to this site and to these trucks.  I just picked up a 87 R20 regular cab long bed 2 wheel drive.  It is rough, but going to be my new driver and fix up toy.

First thing I am doing is trying to get a good baseline to evaluate the condition of all the parts and what can be done to make them work the best.  Currently I am looking at the transmission.  According to the ID page on this site it is a TH400.  The motor it is behind is a TBI 350. 

I do not believe this to be the original trans for this truck.  There is a spade connector on the driver side of the trans about halfway back on the trans body.  It is not connected to anything.  The speedo cable is also just a little short to reach the connector point at the rear of the transmission.  It does have a vacuum port plugged in on the passenger side of the body and it is hooked up (poorly).

My question are, what do you think the original trans would have been?

Can I just pick up a speedo cable from a TH400 truck and it will be long enough?

What does the spade connector need to go to?

The trans feels strong, it will bark the tires going into 2nd under very little throttle, but then goes to the 3rd very quickly. 

Thanks for the help!

[VileZambonie]

That is the connector for the detent solenoid. The Th400 (3L80) was available in your truck. If it's not factory you'll need the switch that mounts near the accelerator pedal and to run an ignition switched fused 12v wire to and from the switch to the solenoid. Is the spid label still in the glove box?

[former520]

The label is in and legible.  Let me know what to look for.

I looked around the pedal and I can see where a switch assembly could have mounted.  I did not see any signs (paint scratches from bolts, etc) that makes it look like anything was ever mounted there.  There is a 16ga non-factory wire hanging on the frame near the dentent.  I will try follow it back and see what it was attached to.