No Start Issue

Assuming the Transmission linkage is grounding the TSS, as per post #2; then;
I always start at the battery cables too, lol, but then I move to the relay, sending battery voltage, from the battery to it, and grounding the transmission side, back to the battery negative, or the block. If it cranks, it's good.
And next would be the bulkhead connectors followed by the connections on the back of the Amp gauge, but, since it cranks by shorting the relay, that last one's a stretch. .