A tale of two 3S-GEs

Code 21 Diagnosis / Starting issues

I couldn't get the car to start from the ignition after installing the oem MT starter relay (driver's side fuse box) and hooking up the clutch switch. Once my NSW from the original auto harness was bypassed, it fired right up. I don't see a need for any additional relays, which I thought was strange since the car had an extra ignition wire added and was very weak on starting. The battery terminals and battery -> starter wire are all new, so there's the difference I suppose.

Ox Sensor (code 21)
I realized I left the Ox ground unhooked with only the signal wire soldered. I grounded it to the alternator bracket, and confirmed voltage at the diagnostic port:



After clearing the codes, the 21 remains, so it seems it is for the o2 heater which I haven't connected yet.