OK. Look at Peteski's photos of the 73199 in his post. (here:
https://www.therailwire.net/forum/index.php?topic=44324.0).
The negative wire from the KA-3 (the black striped wire) can be soldered to any place where there is a green dot or rectangle. On the top of the decoder (the first of the two photos of the 73199 in Peteski's post), you will see two green dots on the RH side of the photo; you can solder the negative wire to the large board traces where these dots are, but you will need to scrape off the insulating paint to do so (use a #11 hobby knife blade and scrape until you see bare copper; scrape away just enough area to solder the wire to). Alternatively, you can solder the negative wire to the green-marked pads where the capacitors (the rectangular yellow things] at the top of the photo are attached. You won't have to scrape away any insulating paint to do this, but make your soldering journey quick: strip and tin about a 1/16" end of the negative KA-3 wire, then hold the wire on the pad where the capacitor is soldered and touch your hot, tinned iron to the wire so that it solders to the pad and edge of the cap.
Now for the blue wire. If you want your keep alive to power the motor, which I assume you do since you're using a KA-3, you must solder the blue wire of the KA-3 to one of the two red spots marked on Pete's photo. I'd use the far right side of the black diode on the right side of the decoder that Pete has marked with a red rectangle, since that is easiest to get to. Again, make it quick - strip and pre-tin the blue wire, touch it to the pad where the black cap is with a hot, tinned iron. No more than a second (it should take only a half-second if you are doing it correctly).
Done.
John C.
