New Mem, 1993 yota 4wd pu- hear click then motor stops

[gwt500]

Hi Removed dash and everything else necessary to replace the heater core. Got it mostly back together. But now

1. Engine nearly quits when the clutch is pushed in.
2. Hear a click and motor just stops. Can't tell where the click is coming from. But probably under the dash?
3. Check engine light comes on then goes out.

Still have a few wires disconnected. Waiting for a part before finishing up. Just the A.C button, heater control switch, radio. Did I miss something? Battery was disconnected whole time I was working on it.

Thanks, looking forward to answering questions here.