Does anyone have an idea of what exactly was done to modify a W126 when it entered the US to recieve it's DOT approval (besides the lights)?

Vehicle was purchased new in '85 in Germany (380SEL) and shipped over here where it had the alterations done in 1989 in Houston, TX.

I was told by the original owner that this was part of the equipment installed to make it DOT approved:




There was also some exhaust work done, but that's about all I know. We don't have emissions testing here, so I'd like to try to return my euro to factory stock.

Anyone have any ideas what that box is or does? Is it like a modern "tuner" box that intercepts sensor input and outputs it's own to the ECM?

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A.S.E Tech A1,A6,A7,A8 & MVAC 609 + EPA 608

Unless stated otherwise, any question I ask is about my greymarket 1985 380SEL.