TH350c Vacuum Switch Question

[Boostaddict]

Since I knew nothing about the TH350c before this weekend (didn't even know I had one) I did a bunch of searching/reading the last couple days. Background info on my question/problem I could use feedback on:

On our '80 k25 the original 350 engine blew a few years ago. Since I was in a bind a friend (who lives a few hours away) trailered the truck to his place and he put in a spare 400 he had on hand for me. Since then the truck never shifted quite right… shifted into 3rd really low (big clunk) and the engine bogged. Auto transmissions are about the only thing foreign to me so I never thought much of it until recently when it refused to start shifting into 3rd (or so I thought). A different co-worker that rebuilds transmissions said he'd take a look at it for me (he also lives a few hours away). He currently has the truck on a hoist at his place. He said it has a th350c in it (thats cool) and that it was the torque converter failure that caused the trans to not shift into 3rd and that it was actually the lockup trying to engage too early that was likely the problem.

So here is my question. He asked me if the lockup wiring is good. I had no idea. He said the thinks the lockup for this trans is self contained with only 1 power wire (from brake switch at fuse box) and he said the wiring is there still hooked up at the trans. After doing a bunch of reading it seems that there "should" be a vacuum switch on the firewall that I suspect was disconnected (electrical or vacuum line) when the engine was swapped and maybe that’s the cause of the premature TC failure. Since the truck is on a hoist hours away I can only look at an old engine bay picture I took prior to starting a clean-up/restoration project earlier this year… is that the vacuum switch in this picture below (arrow)? If so then I don't think the vacuum line is hooked up since the only vac lines on the engine go to the modulator on the trans and another to the distributor. Thanks,

Wayne
BTW, the engine bay looks completely different (clean) now