M151A2 was 2nd military wheeled vehicle I drove. I recall both the RT-524/MT-1029 as VRC-12 and PRC-77/AM-2060 VRC-64 systems in use on the M113A2 based tracks, the MX-7777 right over the Driver's left shoulder, to switch off before starting the track, the big yellow and black decal on the instrument panel being an easy reminder.
But I don't recall seeing an MX-7777 on the M151A2, stateside. It is not a big effort to reach back to flip the power switch on the radio mounted on the curb side rear fender top. I think when dealing with forward deployed units the KY57 TSEC VINSON encryption device comes into play, the KY57 would be nearly impossible to reach the tiny rotary power switch, it doesn't shut off when you power off the radio, it draws power direct from the MT-1029 through the "J Box". Incorporating the MX-7777 Suppressor would allow the drive to shut commo down prior to starting without having to crawl all the way to the back corner of the rear fender to shut off the KY57.
TM 11-5820-498-12-HR is the Hand Receipt covering AN/VRC-64, it does not list an MX-7777 as an accountable item on the inventory list on Page 13.
MX-1244/VRC-46 would be the installation kit for the VRC-64, does not list an MX-7777 as a component on Page 14.
The secondary PRC-77 vehicular installation is the GRC-160 the difference being the inclusion of the Manpack-specific components(ST-138 Radio Carrier[or ALICE Radio Ruck later], AB-591 Antenna Base, AT-271 Whip Antenna, AT-892 tape antenna with spring adapter base, and accessories bag) to allow the crew to continue to utilize the radio when the track was disabled. Or in our case, when we humped the 81mm mortar attached to the dismounted Rifle Platoons.
Slightly different utilization, in Berlin Brigade Feb 89-Dec 90, we had 3 Humvees assigned to the M125A2 track mounted 81mm Mortar Plt in the Rifle Company, 1each 4 door for the Plt Leader, 1each 2 door for the Plt Sergeant, and another 2 door for a Fire Direction Center FDC vehicle, which had several modifications, a map board on the wall and wooden benches with storage for the FDC guys to sit on while operating the M23 Mortar Ballistic Computer. And there were 2 of the VIC-1 Crew Boxes installed in the rear to allow the FDC to monitor and transmit over the VRC-64 radio system with headsets. And I seem to recall an MX-7777 behind the B Pillar curtain to shut down the PRC-77 radio and KY57 VINSON from the back.
2nd tour back in Berlin, Oct 1992-June1994, there was a new MTO&E, there were no longer track mounted 81mm M29A1 Mortars in the Rifle Companies or 106mm/4.2in M30 in the HHC, it was all HMMWV transported, ground mounted M252 81mm and M120 120mm Mortars, still no SINCGARS yet, I didn't see my first RT-1439 SINCGARS until my last 9 months at Ft Carson before I ETSed in 1996.
So officially, there are examples of the MX-7777 being used in some cases on wheeled vehicles employing PRC77 or RT524/246 radio systems in vehicular power adapter mounts and power amplifiers.
After posting, I googled the actual VRC-64 TM 11-5820-498-12, on Page 43 second column near the bottom, it states "The Electrical Transient Suppressors MX-7778/GRC or MX-7778A/GRC is provided in tracked vehicles to protect the radio equipment from electrical transient voltages that may be in the vehicular electrical system. Instructions for installing the installation kit for the MX-7778/GRC and MX-7778A/GRC are provided in TB 11-2300-457-30"
