You hit it on the head. If the circuit acts up again - I will have an ear to the relays to hear if the primary is pulling them on. I get the feeling that the relays have never been touched since 1988 and by simply unplugging them and plugging them back in - better contact was made on the pins. So far all is well. If you could help me understand something - I would be appreciative. I have found out that the temp sensor on the upper rad hose will engage the fan at high speed when the internal resistance goes up because of high engine temp. I have found out that the high pressure sensor on the drier will kick the fan in on high speed when triggered. What sensors kick the fan in on LOW speed and where are they located? According to Mercedes dealer up here - the green sensor on the a/c high pressure will only cut in to turn on the fan if the a/c is on and the outside ambient temp. is above 90F (roughly) Apparently they say that lower outside ambient temps do not cause the a/c to build up enough high side pressure to kick the fan on unless it is working harder from outside higher ambient temps. So far with temps around 77F - a/c set on minimum - car gets cold but engine temp stays below 95C so the fan has no reason to kick on. I guess I will have to wait until I hit Chicago with their 90-95F muggy temps to find out if all is well.