Not hard to do. The beauty of the SPOD is in the switch cluster that looks like it belongs, and the circuit board with the terminal strips and relay sockets. NAPA sells relays that have sockets with pigtail wiring included, so that can really cut down on your solder work, although you may have to drop out specific wires to get appropriate wire sizes.
Follow this simple 10-step process that can be adapted to almost any type of project. Note: I’m a gifted amateur, your project may have as many as 15 steps before achieving the same result...
Step 1 is make a plan:
You’re sure you can do better than them, so only build for what you need
What loads
Where switched
Constant or ignition power?
Low voltage connection
Step 2 make a drawing:
Rough wire diagram from terminal to terminal
Step 3 make a better drawing:
Include wire routing and measure mock ups to get the circuit lengths
Calculate wire sizes from loads and lengths
Step 4 buy all kinds of supplies from Amazon or similar
Step 5-8ish build, f-up, rebuild, f-up, rebuild again, f-up AGAIN!
Step 9 buy the damn SPOD
Step 10 tell everyone how you were going to do your own but you’re just too busy and this seemed like a no-brainer for the price point.