Hi Ive got a 306 d turbo and I drove it out the workshop the other day and down the yard and then after a couple mins it just died and I’ve found that there’s no power going to the stop solenoid so I just ran a wire from the battery’s to test it and it started, so I’m not it sure if i can just run a new wire to it cos i don’t know if it’s fused etc
Every power supply should run through a fuse. Tried looking in Haynes n whether it's pre- or post-1997 the solenoid is powered from a circuit shared with other ignition/security components. Don't definitively know how many amps the solenoid will draw on its own but am going to take a guess it's less than 5 amps.
Unless someone with greater knowledge can jump in with some other advice I'd go for 5A fuse. Presumably you'll need to wire your bypass to a 'hot with ignition on' only circuit or your solenoid won't close when the ignition is switched off.