The 2 coolant temp sensors, one 1-wire, one 2-wire, should both be swapped out. Ignore the extra crap on the S14 motors. If there's a plug on the S13 harness, hook it up. It's that simple. You can leave off 1 or 2 of the emissions dealies on the intake manifold. TPS, dizzy, mafs, ignitor, O2, coolant, injectors. That's all the S13 ECU needs for I/O to the engine. The 2nd coolant sensor will drive the gauge in the cluster.

So I just literally told you everything you need to know about this engine swap from the electrical side. What's next; do you need a vacuum hose tutorial?