How do you install a replacement seat belt on a 1973 MB 450 SL?

Depending on which part of the seat belt you need to replace..... The inboard part of the seat belt...the female receptacle...you need to first disconnect the electrical connection underneath the seat (thick black wire with a connector) then unbolt the receptacle...done. The outboard side of the seat belt...the long part....you'll need to remove the left side panel, where the hardware is to lock down the roof. There's a small, plastic cover over the handle that lifts and slides back. The handle and small lever will slide off. There are about 5-6 small screws that hold the cover on. You'll have to lift up the bottom panel to gain access to some screws and have more room to work with. The seat belt unit is bolted down with a large bolt on the floor. Remove the bolt and the unit will come out. There's also a bolt on the top . You'll have to remove the chrome cover...2 screws in the fron. And, be careful not to scratch the paint. You should be able to remove the entire assembly. Replace the assembly with the new unit, and make sure that you have the belt right side up, otherwise you'll have a messy looking seat belt. Before you bolt everything back together, sit in the car and test the belt set up out...making sure its moving freely. Once all of that's done, and you're happy with the installation...put all the pieces back together. I hope this does it for you. DM