Engine won't turn off with keys out.

Hello all, I have a 1983 1.8 Golf GTI and I'm having a few issues I'm struggling with.

I can't turn the engine off when taking the key out, the engine goes to struggle but remains at a stead idle so I have to stall it to cut the engine. This started 12 months ago after I took it out in heavy rain. I took it for an mot and left it with the garage, turned off fine dropping it off but the mechanic said it wouldn't turn off for them moving it into the mot bay. The footwell's were dry when I got it home so wasn't sure if I had a leak, the car ran fine for a few days after that then the issue started again. Roll forward 10 months and I thought Id swap the fuse board, couldn't see any issues with the one I took out but this seemed to solve the problem. Did a few runs over the next week and it the problem returned. With the engine off and keys out I can hear the fuel pump prime also the oil pressure light and charge light on the dash are on. Today I went to change the ignition switch thinking it was faulty, after unplugging it I reconnected the battery to see if the dash lights went out and fuel pump stopped. No, same issue, oil and charge light come on and the fuel pump still primes. I assume the ignition switch is fine but now I don't know where to look next. I fear it's a dash out wire trace job and electrical issues are low in my skill set!. Anyone any suggestions please?  Any help much appreciated!!

Anyone? Fingers crossed someone has some bright ideas!!