O2 Mileage sensor?

[rumb]

Friend's 1980 450sel, he says there is a mileage counter on the speedo cable that sets off a dash light when the O2 sensor has been used for X miles.

Found this:
https://handbook.w116.org/cd/Engine/107/M117_45/1980/14-050.pdf

weirdly the manual page 15 says just to unplug the device when the mileage reaches 30K miles?

Is there a way to reset the device?

[raueda1]

Sorry I can't help with the actual question, but one question begets others.....

First, very interesting reading.  I'm amazed by this whole setup, which I completely lack.  Seems like a lot to go wrong so I'm amazed that people manage to keep these older cars going at all.  Congratulations to all of you. 
Second, I thought your car was a euro but I guess not?  If not, any chance of pulling all that stuff off and calling it a euro?  I guess CA mandates emissions testing on old cars but UT didn't and neither does CT. Thank god again.  What about CO?  Cheers,

[UTn_boy]

Hopefully this will help. 

[rumb]

"Disconnect plug"   

How utterly unMercedes...

[UTn_boy]

I assume that they mean for us to plug it back in after unplugging it to reset the switch?