I did this on my 83 (sold) and just did it on my 85 300D and took some pics. It saves a lot of time if you ever have to R&R glow plugs. Takes seconds to get the wires off and back on. No worry of losing the 8 mm nuts since you won't need them anymore.
Take apart a female Mercedes connector and unsolder the wires from the contacts. You will need a soldering iron with a big tip. Mine is a big old one probably around 80 watts. Spread the contact a little with long nose pliers to fit over the glow plug electrode.
Cut the ring spade and spread it a little to insert in the contacts like this.
I have 5/16 o.d. nylon fuel lines which fits over the contact snugly without falling off to keep water and dirt out. Before putting the contact on the glow plug electrode, I smear it with grease to keep moisture out. I use extra long, long nose pliers to insert and remove the contacts. Takes seconds, sure beats fighting those 8 mm nuts, twisting off the glow plug electrodes and dropping the nuts.
