i have seen that some people have substituted the o2 sensor from a 90 mustang 5.0 for the factory m103 sensor i found the bosch australia website that lists oem and replacement sensors for a zillion cars seemed like australia models go figure there is a cross reference at the end that lists #258 986 504 as the replacement for 0 258 003 146 (the number on the official mb part in my 91 300e) i went to my local autozone store to get the bosch number off the mustang sensor they had 2 different ones 0 258 003 942 and 953 the bosch catalog had neither listed but did list 0 258 003 950 the replacement for this is 258986502 the catalog lists many ford vehicles from around 1990 with 5.0 engine that would use this replacement number the mustang listed did not have the 5.0 the catalog states the 504 number refers to a 18 watt heating circuit the 502 number refers to a 12 watt heating circuit so it seems that the difference between the mb and ford 5.0 sensor is that the mb(504) will heat up quicker than the ford also the ford is slightly larger in diameter one other note the bosch catalog says not to solder the wires but use crimp connectors because the sensor gets reference oxygen(atmospheric) through the wires and solder may impede this