Wow! I have an issue very similar to yours, I turn on the lights and the turn signals/high beam lights on the cluster come on but I also do not have any dash lights and my tach on my dash stops working. I never paid attention to my temp or battery voltage gauges to see what they do. I figure it's a ground or possibly a short somewhere, I haven't dug into it yet. I'll be interested to see what you find.So I'm having kind of a weird issue maybe someone has seen. Whenever I turn on the light in the car the temp gauge goes all the way up the tach drops and the battery gauge drops. Also the turn signal lights and bright indicator turn on. Not sure why that would happen I've never seen that before. Here's a link to a youtube video I took of it happening. I'm wondering if this is why the temp gauge reads so high right now even when the ECT reads fine and my autometer gauge reads normal.