fasteddy is right. The stock O2 sensor(s) need to be shielded as they are from the factory. The MS really needs a wideband O2 sensor. Sharing O2 sensors between a stock ECM and MS isn't recommended. Trying to tune without a WB is going to make your life extremely miserable (or so I've read ).

For parallel installs the stock O2 sensors remain on the ECM, the WB goes on the MS. The stock sensors are retained to keep the ECU happy (emissions stuff) but that's all.

On stand-alone MS installs, the stock O2s are dumped along with the factory ECM and the MS is installed along with WB sensor(s) to take their place.

Not sure which one you're doing but that's how it's supposed to work. Had my head buried in this stuff for weeks - toying with putting a MS3 in my Sport for fuel and spark.

Edward

[edit]

DIY's shielded wire page

Sorry if this is a stupid question, but why did you go with the MS1 rather than a MS2?