I have been experiencing a stange issue in my lotus for the past few months. Basically if you go out for a drive the ignition wont go off. The engine dies like normal but the power to the dash stays on. It shows the miles , fuel and backlights but you can take the key out and walk away. I think this is what sapped my battery as the car is solid voltage wise at the minute.
I have fixed it quite by mistake. I bought a MFRU ( multi function relay unit ) for a whole £13.99 and didnt get any further than getting it out of the packet. I bought this as on the schematics it controls the ignition and I thought ( incorrectly ) that it might be the ignition relay sticking on.
It appears that when I have studied the electric schematics that there is a fuse that controls the immobiliser. I hadnt had any issues with it , but I know its part of the loop so to speak.
I removed the fuse and in fact all of the fuses in that cluster and placed them back in again.
Car now illuminated correctly and I heard a clunk when I turned off the ignition along with a light that went out.
Job jobbed.