L28 sensors in Open Discussions Posted Sunday at 07:25 PM · Edited Sunday at 07:28 PM by Dave WM water temp switch on my 75 Cali car was for the EGR system. It is disabled during warm up with an electrically controlled vacuum source. I have had a few of both the thermotime as well as the temp switch. Most of the used ones did not function. I presume corrosion was the factor. The temp switch in my case was a NC below 140f IIRC, I ended up making my own with an old housing and a new temp controlled reed style switch, epoxied into place. I think the main problem I had finding a new temp switch was most were NO at below 140f and would close once the engine would warm up. Not what the EGR wanted. I think on others the temp switch had to do with switching the dual coil distributer pickups for different advance one full temp was achieved.