I want to install an aftermarket oil pressure gage. Anyone have a step by step how to guide?
Depends on which one you get. Some come with a sender and are mechanical (easiest to install), some are electronic (good luck).
I have an old bosch one rolling around in a drawer in my garage I intend to toss on my car at some point. I'm pretty sure it's as simple as a power, ground, and signal to turn the lights/gauge on, and then a new sender that I would replace the factory oil pressure sensor with.
If the Capri is anything like the Miata, the factory oil pressure gauge is a bit of a joke. Its more of a "if this needle moves, theres probably some oil in your engine" gauge.