Kenwood TK-706D is a two-channel 25 Watt VHF radio. The Programming Cable for Kenwood TK-706D is KPG-4. This post is about how to build Programming Cable for Kenwood Tk-706D or KPG-4.
Kenwood KPG-4 Compatible Programmer by Kyle Yoksh, K0KN, is the schematic used as a reference to build programming cable.

Kenwood Tk-706D (2 CH) VHF Radio
DB9 and MAX3232 chip used (RS232 To TTL)Make sure to join DB9 pins on RS232 To TTL converter are connected; otherwise, programming will not work.

DB9 Pin 4 and 6
DB9 Pin 7 and 8
Temporary setup while conducting a test. A 9V battery supplied power to the MAX3232 chip.
Pinout on MAX 232 TTL CONVERTER
VCC: to 9V battery +
GND: to 9V battery – and ground pin on RJ12 Kenwood Pin 2
RXD: to RJ12 Kenwood Pin 6
TXD: to RJ12 Kenwood Pin 3
The temporary setup worked, and I was able to program the Kenwood VHF Radio Tk-706D using Kenwood Programming KPG-6D. I thought about making this cable more organized. I worked with my friend John VE7CUU to make a small enclosure for the chip. Then we found one bare metal contained that was the appropriate size to hold the chip and 9V battery.