Hi, and welcome!

• • cooling fan for retarder
    • Can I use an I/0 to drive this fan?  I suppose I need to check if it will run on the 5V output.   
• No that does not work. You need a much more powerful fan. You can buy a relay board that you can control from YourDyno. They are called KmTronic, this one for example: USB Relay Controller - Eight Channel
  • Speed reference
    • I need to add the speed sensor wheel and actual sensor.   
    • Does this get mounted to retarder or rollers?  
• It must be mounted on the same axle as the retarder. Anywhere on this axle is fine 
  • RPM
    • I plan to add an RPM inductive pickup.   
      • high tension wire inductive pickup is straightforward.   
      • Does anyone have suggestions for one that will work with COP setups?
• Buy the Innovate motorsport inductive pickup: https://www.innovatemotorsports.com/inductive-clamp-kit-for-use-with-lm-2.html. It is recommended to change to a shielded cable.

 Is it possible to upload photos?  Or do I need to link from external site?  

 You can upload one photo per post

Cheers

I spent some time going through the coils today.   They are already wired 2P-2S.   Then I started questioning my electrical math.   Each coil rated 96V.   Connecting in parallel does not change the voltage rating.  It just divides the coil resistance by half.   Then the two sections in series will add voltage to get 196V and meet my target.   The two coils in series then restores the wire resistance back to original.   Is my logic correct?   

Reading through the manual each coil is rated 96V.   In this case I am planning 2 series - 2 parallel connection to give me 192V total.   will plan to pair the coils 180deg across for parallel.   

Any Concerns here with this proposed setup?  

I also found that there is an integral speed sensor.   In this case, I answered a question above about mounting the external speed sensor.  I will just use the existing one.   I will also use the integrated temperature sensor on the eddy current drive as AUX in.   Hoping I can set software limits based on temperatures.   I will just need to figure out calibration factors for each of these sensors.   

FYI.   I just found an online manual for this dyno.   It was also sold under SnapOn brand.   Quick read might answer some of my questions about wiring.   

https://www.snaponequipment.com/common/serviceparts/mahaasmhp.pdf