I had modified a few w124 relays to incorporate the vw99 relay. Basically you remove the Mercedes relay from the printed circuit board and graft in the vw circuit board. Careful the vw relay comes in 2 forms the adjustable and the non adjustable relay. The relay with an arrow is the adjustable 99 relay. It's been years since I had done this

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92 e300d2.5t
01 e320
05 cdi
85 chev c10