My 2003 Jaguar (4 height sensor model) has an issue where the front suspension inflates until its at maximum.

I have had a look through the posts of here but cannot work out what the issue is.

Scan tool shows open/short circuit to both front height sensors, both front struts, and the vent solenoid. I have tried to deflate using scan tool to no avail.

'm picking that it maybe a wiring harness issue or a ASM issue. I have checked the vent solenoid by bench testing it and it appears to move correctly. There is a 3rd plug coming from my compressor which has nothing plugged into it and I have found near the radiator a Blue and Black wire in a stand alone harness which have been soldered together, the length of the harness is correct for being able to reach the compressor however have been hesitant to connect these together as the coloured wires coming from the compressor do not match the blue / black harness wires.

The previous owner has attempted to fix the issue by installing a new solenoid block in the back, apparently was doing this before the change so clearly didn't fix it.

 

Have had a look at the wiring diagram for the suspension system and some of the items you describe as showing open circuit on your scan tool (LH front height sensor, LH front strut and compressor vent solenoid) share the same electrical connector EC61. The description/location of this connector in the electrical guide is as follows;
EC61 22-WAY / NATURAL / ENGINE COMPARTMENT HARNESS TO CABIN HARNESS
Maybe your inkling that its and electrical problem is correct. Might be worth tracking EC61 down and checking /cleaning and see if it helps