1982 70HP Johnson J70TLCNB Tach and Controls

Couple of questions concerning the controls and adding a tach.

The pic of the controls show a knob labeled Throttle/Friction/Accelerateur...what does this actually do?

The harness below has a purple wire I believe is sending information to my trim Guage. There appears to be two empty ports on this harness. Can I utilize this to add a Tach? Which port to use or do I need to open the controls to verify? Any Tach recommendations?

The Tach guage is always in the UP position as seen in the pic? The previous owner said you can recalibrate the sensor but why bother when you can just turn your head....is it difficult to recalibrate? What stops it from working properly? Are these guages original? What is the purpose of the toggle switch below?



Thanks!

Throttle friction controls how much effort it takes to move the throttle handle.-----And holds the throttle handle in position should it want to move by itself.-----That plug in is meant for the tachometer.----Purple wire supplies 12 volts for light in the tachometer and other gauges.

Thanks!
Does anyone have a wiring schematic that would show the purpose of the other two plug spots next to the purple(power). Must be one for ground and one for Tachometer?
I looked at the control and it does not look as simple as a couple of screws to open it up.

Is there a process to recalibrate the Trim/tilt at motor so guage reads correctly? I have read some that say this feature is not reliable and not worth any effort. Correct?

That plug in location is for a tachometer !----Just 3 screws and the control splits.----Not sure why you say it is not simple !-----Find ----mastertechmarine----or----maxrules--------Just click away to find the wiruing diagram for your control box.----Bonus for you , as it indicates clearly that the plug there is for the tachometer !!

Tachometer plug should have wires for 12V power when key is turned on (purple), tachometer signal (grey) and ground (black).