Here is a link to Kent's kits - mercedessource.com Kent explains the advantages of parallel wired pencil glow plugs first introduced in the 1978 US model 300SD and then later in the 1980 123 chassis diesels. The automatic relay can often be the weak link in the system. Mercedessource offers a kit you can install yourself that will allow you to bypass or "override" the factory wiring and relay and allow you to control lighting the glow plugs yourself with a push button mounted on the dash. Can be adapted to the 1978 to 1985 300 SD, the 1980 to 1985 240D 300D 300CD and 300TD, and to later 201, 124 and 126 diesels as well. Highly recommended for very cold climates and if you are running waste vegetable oil.