There are many references to how the T5 and T5.1 mirrors have different wiring. I encountered that today.
The left hand, near side in the UK, mirror on a VW Transporter T5 was damaged. I helped to replace both mirrors with the newer T5.1 style.
When connected without modification the T5.1 left hand mirror has reversed operation when plugged in to the older T5, the up down control moved the mirror in and out and the in out control moves it up and down.
The fix is very easy, simply swap two wires in the connector. On the original connector this is swap the grey wire and the purple wire positions.
To make things as confusing as possible, one of the other wires is grey with a purple stripe. Very difficult to differentiate without looking very closely.
To my surprise the right hand, UK drivers, side worked correctly without modification.
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