Here are parts in current and recent use.

Part Part Number Image Recent Source
Air charger unit, single output. PK-D12F
Drok DC voltage converter/regulator, wide range of input, 5 VDC output.
Note the waterproof packaging, rather nice for the engine environment. Drok and other makes also have similar units with screw-adjustable voltage output.
Fuse tap for any size fuse.
Many on the market are rated at 10A max, which limits which OEM fuse socket you can safely use.
Car Add-A-Circuit
3M Dual Lock fastening material.
I laid a small bed of this in the air filter compartment, then cut sections to size to hold each item.
These things are great. They keep wires very securely connected, protected enough, and nicely removable too. They come in lots of shapes and sizes. This is the kind I’m using so far. The link is to a two-conductor version. One can buy an assortment at astonishingly low prices. The only catch is, you’ll need to put them where rain doesn’t go.
Temperature-controlled switch.
This is an excellent component of standard part number, made by quite a few different manufacturers in different locations, and the prices have been going down, not up.