[R-390] R-392 but really PRC-47 question

[James Green]

This may be a bit off topic, but I can't seem to find a PRC-47 forum. Also, the GRC-19 R-392 also uses the same audio connector so maybe someone here can answer my question

I just got a advertised as unmolested and working PRC-47 transceiver. It came with almost none of the accessories. The only extra I have is the DC power cord. This beast operates off 28VDC 20 Amps or 120VAC 400Hz. It’s Vietnam era and manufactured by Collins.

I have a LS-166U speaker that has the same U-77 connector on it that I use for my R-392. I connected it to the PRC-47 figuring the pin-outs would be standardized. In fact it seems to work fine on SSB but as soon as I switch to CW it goes into Tune mode. I suspect the LS-166 or the U-77 connector has a jumper across two pins that are used for the CW key on the PRC-47.

I have paged through the manual and can find no mention of the pinouts for this connector. Does anyone out there know what they are?