The bike didn't have to be electrical to become "possessed". Remember at the baseball game, the kid's bike flipped him off of it before he got ran over by the steamroller.

None of the M16s or UZIs in the gas station turned on them.
Trying to make sense out of Maximum Overdrive is a lost cause.

The M60 is a machine gun. The machines came to life. Why wouldn't that include machine guns?

They really should have sat down and decided what could and couldn't be possessed; the scene with the gun mounted to the Mechanical Mule firing away always bugged me. The vehicle itself I can understand, but the gun should be independent from the possessed vehicle.

When tanker truck drops its fuel load into underground storage tanks, no one opened the manual valve on the tanker to permit this to happen. Valve is seen opening itself.

i dont know what you mean by truck tank gas valve, do you mean the scene where the guy gets sprayed with diesel?..i guess its possible the gas pumps were controlled by the aliens
to answer your question on the goblin truck Turing its mirrors. Yes in 1986, it wasn't unheard of to have electric mirrors in cars/trucks. You clearly see the truck start its battery switch and go into electrical mode, so it can move the mirror

Well, remember, a hammock was seen swinging by itself

Maybe it was a windy day? Or else it was one of those battery-operated hammocks!

Well, remember, a hammock was seen swinging by itself

a bike was safe bc no electricity or batteries- everything else was connected somehow to things that the comet could control