Yes, I'm running an RCCI voltmeter converted from an ammeter on Big Blue. But I didn't wire it the way the instructions say. Instead, I wired it as shown below.
The wiring already runs from near the starter relay to the ammeter. And I wanted battery voltage not in-cab voltage since the latter changes with whatever you have turned on in the cab. So I wanted to continue to use the Red/Orange wire that sends battery voltage to the ammeter.
But, you want to only turn the voltmeter on when the key is on, otherwise it is on all the time and pulling power from the battery when the truck is parked. So I put a relay in the ground side of the wiring, the Yellow/Light Green wire, and pulled it in using key-on power.
Gary, AKA "Gary fellow":
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Dad's: '81 F150 Ranger XLT 4x4: Down for restomod: Full-roller "stroked 351M" w/Trick Flow heads & intake, EEC-V SEFI/E4OD/3.50 gears w/Kevlar clutches
Blue: 2015 F150 Platinum 4x4 SuperCrew wearing Blue Jeans & sporting a 3.5L EB & Max Tow
Big Blue: 1985 F250HD 4x4: 460/ZF5/3.55's, D60 w/Ox locker & 10.25 Sterling/Trutrac, Blue Top & Borgeson, & EEC-V MAF/SEFI