l had a heated windscreen fitted (to my 110 TD5) last November
And just got to installing the wiring yesterday.
Does anyone know if it matters which side of the screen is positive and which is negative?
lt's a two wire screen and looks like it doesn't matter, there's no markings on the screen to identify positive and negative.
l connected positive to the RHS as it worked better with the wiring harness and there was a handy earth on the LHS (one of the wiper motor mounting bolts)
Then, after l had finished the installation, l read the instructions (!) with the harness and it said "positive normally on the same side as the battery box"
Which is the opposite side to what l have done.

Hopefully on the two wire screen it doesn't matter, as l don't fancy taking it all apart again.
Pressing the button does provide power to the screen, so in that respect it appears to be working.

I wouldnt have thought it maters. Same as a light bulb?

Hopefully yes

As @mick the builder , normally they're just a bi-directional element but some car screens/older screens have either a load resistor or zenner diode built in for current regulation :. there's an input and an output = current flow. May be worth checking with the supplier just in case...or measuring across the contacts for current flow off the Landy by hooking up a 12v battery.

Well, l had condensation on the screen today and the heated screen appears to work fine.