Well yes...I have to agree that it would make a lot of sense to install the wire anyway. On my 300D, the cluster pops out easily. On my 560SL, I have to remove the steering wheel -- which means disconnecting the air bag. Not really so hard either, but it is extra steps. I would assume the W129 chassis is more involved too.
Before installing the wire, I would do some more research and make sure this is applicable to you set-up.
