1971 Volkswagen Beetle smoke

If its a plastic smell burn you have a direct short to ground, you need to find it otherwise the car can catch on fire

I had the same problem after I had a radio installed into my 73. What happened was the plug behind the steering wheel came loose and was just barely on. I just had to push it back in further. I wouldn't do anything with the electrical until the positive and negative terminal wires get disconnected, otherwise you run the risk of being shocked if you touch a live wire. Once you think you've fixed the problem, tighten the wires down tightly and then try it out.