You will blow a 1.5 V bulb! It's the output of the bulb that matters, use the wrong one and you can end up damaging the drivers in the ECU, there are special 'NOID' lights designed for just this purpose.

Matt, you are correct re the overheating strategy, 1600 is between the plugs and 1800 is on the right hand end of the head, it is used for the temperature gauge as well, it is worth checking though, as you say.

Don't assume this is caused by the cover, it may well be removing the battery has caused it, bad PCM's have been known to cause this issue before.

Martin