I assume if it has 3 contacts you will need 3 relays as it will have 3 zones. I was told on the weekend the ones with 2 contacts have 2 zones that work with separate relays. I assume 3 means each zone draws less current individually??
(This is an assumption though)

I would expect three contacts to be a two zone windscreen as one contact will be a common earth return, therefore you only need two relays.

Information gained so far.

1, early heated screens have 3 contacts which heats 2 zones left and right sides
2, later screens have 2 contacts the heating element covers the whole screen.
3, both use only one relay
4, both use a timer to auto switch off the heater element after aprox 5 minuets
5, both can be switched off prior to the timer completing its cycle or reactivated directly after the cycle
6, too ensure the screen cannot be activated when the alternator is not charging an oil pressure switch is used. This switch connects the relay to earth only when there is sufficient oil pressure e.g. the engine is running
7, the screens are rated at 40 amps
8, the LR fitted relay is rated at 70 amps (giving some safety margin)
9, both 2 and 3 contact screens are available in clear and tinted
10, screen prices vary considerably Pilkington glass is standard fitment and an after marked product is available made by Pilkington's (advised some cheaper options would be a poor choice)
11, sealing rubber prices vary considerably some cheaper options are of a poor shape do not fit correctly from day one potentially it can let in water from day one. The use of a sealing compound stops it but only for a short period of time LR supplied rubber is good quality
12, BE AWARE if you were to supply a LR sourced seal to a fitting company (to ensure you get the good seal fitted) asking them to use it instead of their own it may invalidate any warranty they give

The only questions still not answered,
Q when in use is there a difference between the two options of screen?
Q is one more efficient than the other at removing ICE from a frozen screen?

Tim4x4, thanks for that. That's really useful information. My window seal is cracked and I'd like replace it (with OEM Land Rover seal), but I'd also like a heated windscreen, and sadly I cannot justify that cost at the moment.

Anyway, thanks for the info!

I don't really see a need for a two zone if you have a descent size alternator which can power both sides at the same time. How often would you decide that you only want to defrost the driver side only and leave the passenger side iced up? I can see if you have a piddly little alt (45Amp) then you may want to do one side then the other but I think most of us have higher current ones that could handle it. Personally assuming a good alternator I would opt for the single zone as it would simplify the wiring slightly.

Kwakerman said:

I don't really see a need for a two zone if you have a descent size alternator which can power both sides at the same time. How often would you decide that you only want to defrost the driver side only and leave the passenger side iced up? I can see if you have a piddly little alt (45Amp) then you may want to do one side then the other but I think most of us have higher current ones that could handle it. Personally assuming a good alternator I would opt for the single zone as it would simplify the wiring slightly.

Click to expand...

I see your point Kwakerman but the factory standard switching did not allow for independent use of the two zones one switch one relay both zones on together.
A good point you make with the size of alternator fitted but you would have to wire and switch each zone separately to be able to achieve that set up.

I have not got to the bottom of why two zones this was the earlier factory installations later installations were one zone.

I have decided to purchase the later one zone tinted screen as no one has come up with a valid reason for the two zone option.

Tim4x4 said:

... as no one has come up with a valid reason for the two zone option.

Click to expand...

OK, I'll come up with one!
If you wanted to do a "half-power" you could switch the same draw of power between the two sides. I.e switch between left and right, say every 0.5 seconds or so. To the car the load would seem the same (not the same as "full-power") instead of switching the heater elements on-off-on-off, or to burn off some excess heat in a resistor.

:scratching_chin:

TheJoker said:

OK, I'll come up with one!
If you wanted to do a "half-power" you could switch the same draw of power between the two sides. I.e switch between left and right, say every 0.5 seconds or so. To the car the load would seem the same (not the same as "full-power") instead of switching the heater elements on-off-on-off, or to burn off some excess heat in a resistor.

:scratching_chin:

Click to expand...

Joker yes that would work to reduce the load on a small alternator, it would though take twice as long to clear the screen.
Yes it would get you up and running with a heated screen if you had a small output alternator.
What I am trying to establish is why did Land Rover fit a screen with two zones?
The circuit and switching would only allow the two zones to operate simultaneously so the power saving option you give would not be a factory setup.

Wild guess but possibly made as a two zone early on in production because a single zone was too difficult to manufacture reliably due to size of screen and the equipment available. As technology got more advanced single zone became easier / cost effective?