While I don't have the 124 series, I have a '95 SL500, my engine wiring, upper and lower went really bad. I changed the upper and have made two attempts to change the lower and gave up because it was cold outside (in Cleveland it was 20 degrees in December, slightly warmer in the garage) and I was not able to get enough "clearance" under the car to remove and route the lower wiring harness. While most is accessible, its hard to work on your back with only a foot or so of clearance. Part of the harness routes around the underside of the motor and trans and its also hard to see. I am waiting for the weather to warm and rent a nearby garage and hydraulic lift to have better access and visibility. Cost of the upper harness was $769 and the lower harness was about $200 from Phil @Fastlane. Neither are difficult replacements. I am going to remove and have the ETA checked and possibly rebuilt to complete my wiring overhaul. Good Luck, Steve