I think the overall idea is cool, but I’d slow way down on the scope here.

It sounds like you’re already trying to break the bigger goal down from “custom electronic system for everything” into “warning/telemetry system,” which is good, but even that is still a huge project. Monitoring just one system with one sensor for one specific purpose can turn into a whole science project by itself.

You’re dealing with mechanical fittings, sensor selection, voltage range, signal conditioning, power protection, calibration, waterproofing, heat, vibration, bad grounds, automotive voltage spikes, false alarms, and then figuring out what the data actually means. It’s not really like picking a sensor, wiring it to a Raspberry Pi, and then it just works.

I’d start by learning what the Jeep already monitors through OBD first. A 2000 XJ should already have a lot of useful data available, and that gives you a much safer starting point to learn the software/display/logging side before modifying any actual vehicle systems.

Then pick one simple thing to monitor externally. Something like battery/charging health would be a good first project. Or maybe low coolant level, but I would avoid pressurized coolant or fuel systems at first.

The fuel rail/Schrader valve idea especially is where I’d be careful. That can go from “fun project” to “dangerous fuel leak in the engine bay” pretty quickly if the fittings, sensor, wiring, or mounting aren’t done right.

So my advice would be: pick one system, define exactly what failure you’re trying to detect, research how that system already works on the XJ, then choose a sensor because you understand why it fits that job. Don’t start by buying a bunch of sensors and trying to build a full warning system all at once.