I'd like to convert my 1980 280TE 4 spd manual trans with Mechanical Speedo over to a Getrag 717.402 5 Spd manual from an 84 280SL with a electronic cable output. I have the electronic speedo from the 280SL. Should I just need the original speedo to trans wiring from the 280SL, or is their more components needed? It also might be easier if I obtained an instrument cluster from one the years that the W123 cars had a electronic speedo, then trying to adapt the 107 electronic speedo into my existing cluster.
Can anyone be of further help?

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83 280TE- 5 spd, 16.5mm rear sway
85 280SL- 15" Bundts, 5 spd