After "tidying up " my engine bay , cleaning up wiring , and spraying the inner wings , i put everything back in place , or so i thought. However , being my usual badly organised self , i lost the piece of paper that i had noted down all the wiring on! Unlike the later SL models the 73 450sl has two ballast resistors in the coil circuit , to reduce the throughput to around 9 volts. At present there is no spark at the coil , and i suspect i have replaced something incorrectly.I have tried running an additional earth from the coil to the chassis, but still getting no spark. The car is negative earth , and checking on an American forum it appears the coil should be earthed from the positive terminal? There is a break in the ceramic housing on one of the resistors , but the "element " appears intact. A local motor factor is trying to locate a new coil and resistors. It appears the coil is specific to a few 70s mercs. Any ideas/diagrams would be much appreciated. I had thought that any 12 volt coil could be substituted , but apparently not.