Electrical germlins

My 86 Porsche 944 has some electrical gremlins. Whenever I turn on a switch like the headlights, fog lights, rear defrost (etc etc..) it causes my temperature gauge to quickly jolt up a little bit. Turn them off and it jolts back down. Its just a small amount, but enough to be noticed. This just makes me wonder because the car runs warm, up around 3/4. Runs warm on the highway and cools down when driving around town. Maybe the electrics are connected to this. What's the problem here?