Coolant Level Warning Light

[Foxyn 2]

Hi, this is my first post so please be gentle!

 

Earlier this evening I decided to whip off my ignition amp and put some heat sink compound on the back of it. So removed the coil and the plate it bolts to. Quick 5 minute job, or so I thought.

 

After I'd put it all back together, I noticed the coolant level warning light was on permanently. I checked the coolant level and it seemed about right. I tried unplugging the lead to the sensor and the light went out.

 

The weird thing is the light wasn't on when I backed it out of the garage prior to working on it so something makes me think I have disturbed something. Does anyone know if there is anything I could have disturbed when working near the coil that might have caused this? Could it be interference from the king lead perhaps? I suppose the sensor may have just chosen this moment to pack up but seems a bit of a coincidence.

 

Any advice appreciated. It seems everytime I fix something, something else decides to break!

 

(Car is a 1.6 '89 with the round header tank and sensor which slides in from the top).