So my Jag is almost complete but one problem I'm running into is some wires burning.

The wires burn only when the engine turns over, you can turn the key to the 3rd position and it doesn't burn. It's one particular wire in the cubby where the stereo and the AC & Heat knobs are, none of those units are currently installed yet. Looks like the wire that's the culprit is red. I've got some photos:

The last photo is most clear, and fyi an aftermarket stereo was installed at one point.

 

Pretty weird.

When the key is turned to "start" (as opposed to merely turned "on") there's only one additional wire at play: the white/yellow wire from the ignition switch that energizes the starter relay and powers up the bulb-check unit in the RH component panel below the glovebox.

Has any of the wiring at the ignition switch been tampered with?

I'll do some more mulling

Cheers
DD

 

Looking at an late XJS wiring diagram the starter wire runs out to the starter solenoid where it is coupled to an wire on the diode pack, probably to power up the fuel pump when cranking. As doug said the only other wire off the ignition switch to receive power is the white yellow one that runs to the bulb check unit.
Ide be inclined to take the cover off from under the steering column and cut the smaller white / yellow wire and see if this solves the issue. Cut it with enough length to reconnect it later on if you so desire. If it still burns then the burnt wire may be the wire that runs from the starter relay to the inhibitor switch, although I cant see it having enough current passed through it to do that unless someone had really stuffed up the wiring of the starter relay.
The starter feed from the ignition switch also runs into the diode pack that's next to the starter relay to provide power to the fuel pump and cold start injector under cranking. Otherwise the other possibility is an issue / short in either the cold start injector circuit, the fuel pump circuit or the diode pack its self. The only wire I can imagine running through there from any of that is the fuel pump wiring.

Oddly enough I had an issue with my car where it would constantly provide 8 volts to the starter solenoid regardless of the key position and burnt out a few relays on me before I picked up on it. Someone has also jumped the fuel pump so it runs constantly as soon as the ignition switch is on so who knows what is going on there. Come to think of it its probably an issue with the diode pack feeding power back into the circuit from elsewhere. One day ill sort it out, for now (meaning the past 2 years) all its had is a wire from the back of the ignition switch to an relay sitting behind the brake booster that provides power directly to the starter solenoid, this wont work very well for you unless your fuel pump is rigged on too.

Regards,
Jay

 

I recently replaced the burled wood dash and messed a LOT of wires. I may have messed something up. I'll check to see if cutting the white/yellow wire fixes my problem. I'll do it sometime this week then report back. Thanks guys!

 

Check and replace your ground strap that goes from the starter to the body. The starter could be partially grounding through the light gauge wires because this is the path of least resistance but the wires are over loaded and they burn up while cranking.