Mercedes 450SLC

Wiring harness issue. Reseat any and all connectors from the battery to the distribution box (there may be two of those depending on the model year) and reseat all of your fuses, if any of them go in too easy then use a small screwdriver to force the contacts to be closer together (or slightly twist the fuse tab, not the most elegant solution but sometimes those contacts in the fuse box are so far recessed that you can't get at them). Good luck!