Toyota Repair: 1992 Landcruiser engine code 21, o2 sensors, oem type

Question
My cruiser just had a new exhaust, dual inlet cat, and O2 sensors (Delphi,)all aftermarket, installed and I can't get rid of my code 21.  One O2 sensor is for left and one for right installed ahead of cat on the downtubes.  My shop manual says "main" and "sub" O2 sensors, which is which?  I took the vehicle out for the recalibration after pulling the EFI fuse and re-installing and as soon as I started it the "Check Engine" light came on.  I did the recalibration three times and no luck.  The vehicle has 207,000 miles on it with the original engine, no white smoke out of exhaust, no rough idle, and oil changes every 3000 since I bought it at 99,000 miles.  Any suggestions Ted?  Thanx!

Answer
The main O2 sensors are the ones in front of the converter, the sub sensors are always located after the cat. The check engine light turning on as soon as the engine is started indicates an open circuit in the wiring or possibly the wires not connected correctly if the sensors were of the wire in type instead of the OEM type which have connectors that plug into the wiring harness.