[R-1051] Another R-1051D modification question?

[Nick England]

So this 1051D and several other 1051's I have seen have got a 170-850
toggle switch added to the front panel (center front). I traced the wires
back to pins 4 and 5 of J16 which connects to the A1 Mode Selector module.
Internal to my Mode selector pins 4 & 5 don't connect to anything. So I'm
guessing there was a mod to the Mode Selector to change something (BFO
freq??) for receiving FSK at 170 or 850 Hz shift.

Anyone know more about this?

Cheers,
Nick England K4NYW
www.navy-radio.com