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I spliced into the Rotorway harness for power (red) and common ground (black). You need to take your time and derive from the schematics which wires connect to which function. I found it helpful to write the wire colors on the schematics. The process is simple but frustrating. I also labeled each wire as to function regardless of it's color.
To install as a fully redundant rotor tach you must fabricate a new mount bracket for the sender. It needs to extend lower than the original bracket to clear the original bracelet. On my installation 3" sufficed. The bracket is made from 1" square steel tube available at Home Depot / Lowes. I welded in a 1"X1" square 3/16" thick plug.
The wiring of the harness was straightforward and well documented with the gauge instructions. However, the sensor, cable wire, D15 connector and OEM Rotorway harness use all different color codes! In the picture above note that the two purple shaded wires are only used with a RDAC. I separated the rotor tach wires from the engine tach wires for clarity. The Molex is the rotor tach harness.
This is the rotor tach schematic, to use, which is included with the gauge instruction manual. Note: that I used a different sensor. Al Yard recommended the one that I installed due to ease of installation and adjustments. Also note that the resistor called out in the print is included in the kit. I did the resistor splice at the sensor pigtail and used heat shrink to encapsulate the assembly. Again, keep track of the wire function not the wire color when connecting. None of the wire color codes match!
The bracelet was a challenge. I desired two nodes for the sense to provide more fidelity. This billet collar fit my requirements.
The Hall Effect sender I used was part number GS100502 from Digi-Key. The cost was $32.03. This installs much easier than the one sold with other MGL products.
This chart was developed to program the gauge yellow, red and green operating zones. Follow the instructions that come with the gauge and use these numbers as a starting point. As you gain experience with the unit you may desire to change some of the parameters. For example: you may decide not to have the "alarms"
MGL Dual (Color) Digital Tach
Originally I planned to use Cap Screws for my nodes. Turns out that the sensor actually picked a signal from each edge of the Allen head. I ended up using common AN4 bolts with a short spacer. In the picture above you can see the new billet collar mounted below the original tach bracelet. I used LockTite to secure my AN4 nodes. Rotate the mast slowly, by hand, to ensure proper clearance between the nodes and sender. I used a three pin Molex connector when I fabricated the three wire cable harness to facilitate installation.
This is a picture of my installed gauge. The Piezo horn above sounds whenever an alarm point is met.The gauge fits into a 2 1/4" hole. I replaced my full range engine tach with this unit and now have full redundacy.
I sourced this collar from Ruland (ruland.com) Manufacturing part number SP-26-A for $40.00. My collar was for a 1.5" mast. For the 1.75" mast you would need the larger collar from the web site chart. I allowed an 1/8" for the mast safety sleeve. My chosen ID was 1.625" (1 5/8"). I drilled two matching holes, one centered in each half section (picture). Tapped the holes for 1/4 X 28 bolt. In my case I used a mill to provide a flat surface so the spacer would seat flat. This also could be accomplished with a disc sander.