Homeless Head-Trading Zombie

by Andrew
(Riverside, California, USA)

I'm looking for the name of a 70's or 80's movie that about a homeless man who somehow becomes infected and turns into a zombie.

He travels throughout the city taking various victims' heads and placing them on his own body.

In the end, an ambulance is driving down the road with, presumably, the dead zombie in the back, only to have his arm come around and grab the driver in the final shot.

Any help would be greatly appreciated!