Where do I find the overload relay on a 500 SL 107 ?

My 1982 500 SL won't start (again). I found out it won't fire (no sparks at the plugs).
As I disconnected the battery very often last weeks, maybe the
overload relay has gone. I tried to check for it in the fuse box, but I only see grey fuses, not one with a fuse on the outside (as it should look like, I think).
Any ideas where it could be located on a 500 SL ? Or other items that could make fail ignition ?

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