If you have an original K3 rated for 500 mA @ 12V on the +12V jack,
you will need to provide a *separate* 13V @ 500-700mA power supply
directly to the +13.8V (coaxial) power jack on the MK II.

The voltage drop in the unmodified K3 was too much (dropped below
11V on transmit) for reliable operation of the MK II or MK III.

If you have a K3s or *modified* K3 (one that has the sticker that
says +12V @ 1A), the MK II or MK III can receive power via the
RCA plug marked +13.8 *IF* you properly set the jumper inside
the MK II/MK III for "DB37 power".

73,

... Joe, W4TV

Yes

manual say this is for accessorry devices.

on my microham microkeyer II i have a rca connector labeled. +13.8v.  the blue wire.   is this where the  rca connector goes?

this might be why i have no power on the mkii?

tnx Niece