I purchased 18 used units from Alaska. There was an extra red wire added, and I eventually confirmed that it had been put in as an ignition sense. It's soldered to pin 4 of J8, the one that is connected to Q44 (on page 31 of the F510 Service Manual). The tech who added them had a .47 capacitor to ground near the soldered connection. Don't know if that's necessary.
From an IC-F610 Transceiver Technical Report, item 5 Ignition SW function, they have the following:
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This function turn ON and turn OFF the transceiver, via condition of car’s switch key.
Usually to supply the power of transceiver, directly connecting to the car’s battery is recommended,
but in case that driver forget to turn OFF the transceiver after leaving the car the battery will be
discharged, so this function is designed to work with car’s ignition key.
Setting requirements
Cut the following coffee beans: On main unit, cut the pin #4 of J8
and connect the ACC SW of car’s switch on this line.
Operation
FRONT SW “ON “condition:
IGSW : H -> Power ON condition ->ON
IGSW : L -> Power OFF condition ->OFF
FRONT SW “OFF “condition:
IGSW : H -> Power OFF condition ->OFF
IGSW : L -> Power OFF condition ->OFF
Setting
Set the following items in cloning software:
On COMMON window -> Expert window -> etc item
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As indicated above, there's no mention in this about the bypass capacitor.