not hard to switch at all really, only bitch is runnin the wires through the firewall everytime and finding a place for the gauge to sit since it wont be permanantly mounted.....one possible problem, that i just thought of after typing that..... you need to weld another o2 bung into each persons exhaust system somewhere to make it read as accurate as possible. even if you had to do this, plugs are made to screw into the bungs so exhaust gas wont leak out.
