They are an accessory item in most countries. You would see a cord that would plug in to the house, the cord usually is behind one of the headlights. I want to say it would be installed in the right side of the block.
Easy way to test is to use it and see if the block is warm in the area of the heater. Unless you have a easy way to test the current comsumption of the heater.
To replace them you unscrew them from the block and install a new one, sort of like replacing a spark plug but way more mess. It will be tighter than hell.
There is no wiring to the car for this at all, just the cord which plugs in to household current.
You can check the wiring to the heater and make sure it is plugged in to the heater on case of no continuity. The circuit should be close to 0 ohms.

__________________
Click here to see the items I have up for auction at EBay

Click here to see a photo album of my '62 Sprite Project Moneypit (Now Sold)