[Elecraft] KX3 and Chinese MX-P50M 45w amp

[MIKE ZANE]

Need a little help. I just bought a KX3 and have it working OK. I also have a 45w amp that I would like to work with the kx3. However, with no info on the keying line coming from the amp, I have no idea if its Ok to use. I see in the Elecraft manual that the "keyline" and tip would be used to connect to key the amp. I can't which of the sections on a TRRS jack to use. Ring 2 or ring 3? Also  don't know how much current is on that amp key line. Measured 15V DC when it is on and off measured 400 ohms, if that is any help. Any one got any ideas on this? Thanks,  Mike