Q: Dashboard lights not working

I was working on fixing some minor problems in my car. I just replaced the gear in the odometer, and now I’m working on the electrical part of the dashboard. The dash lights weren’t working at all, so I pulled out the bulbs and sanded the corroded areas in the plugs while I worked on the odometer. Then I put the dashboard back in, and all the lights came on and worked! But when I turned the turn signal on all the dash lights flashed at the same time the turn signal was flashing and along with the needle for the fuel gauge. The headlight flashed and worked properly though. And when I turned the right signal on the green left arrow on the dash blinked brighter than the green arrow on the right. When I turned the left signal on the green arrow on the right flashed brighter than the green arrow on the left as if they were reversed. I have heard of this happening with a bad ground in one of the headlights. So I took mine apart, and everything was OK. I also found a wire behind the dash not connected to anything. And I can’t figure out where it goes. It’s a small red plug. I checked the dashboard and there are no wires missing from it. Do you know what might be going on? Do you have any ideas?