The round "time switch" was first used in the late fifties and early sixties fuel injected engines prior to the W113 cars. This was referred to as "version I " starting aids. It was used in conjunction with one of the four prong rectangular relays which operated the injection pump enrichment solenoid. In this instance the round time relay activated the IP enrichment solenoid for one second at engine temps above 113 degrees F for one second. Below this temperature the round time switch is inactive, and the IP enrichment solenoid activates via one of the rectangular relays when the starter is activated. Starting Aids "version II" includes the early 230SLs. The round time switch is still used in this version. It is again used in conjunction with a rectangular relay which activates the IP enrichment solenoid also. With this version the round time switch actives the rectangular relay which activates the IP enrichment solenoid as previous. In this case the round time switch operates for one second at engine temperatures above 41 F. Below this temperature, the round time switch is inactive and the IP enrichment solenoid is activated via the rectangular relay only and the TTS. Version III starting aids {later 230SL), used one rectangular relay and one round time relay. Here again the round time relay worked in conjunction with the rectangular relay. In this case the round time relay operated both the IP enrichment solenoid and the intake starting valve for one second at engine temps above 95F. Below these temps, it was operated by the TTS and same rectangular relay. Version IV starting aids, (Aug. 65- 1970) no longer used a round time relay but used two rectangular relays. One for the IP and the other for the intake. With this version an optional upgrade could be added to improve starting at higher engine temperatures. This kit incudes once again a round time switch, and some additional wiring. Here again it is used in conjunction with the one of the rectangular relays. Version V was the simplest. It had only one rectangular relay for the intake starting valve. No round time relay. No enrichment solenoids on the IP at all ! Quite confusing. Start off by identify which version you are working with first.