Heated Rear Plastic Window! - How to have one.

This mod was inspired by Sheila, who was saying 'What a shame it doesn't have a heated rear screen, as sometimes it mists up.'

Mmmm, thinks I, well I'm not paying for a glass screen + fitting, just so that once in a while we can demist the screen.

I remembered seeing somewhere that a guy was using a little plug-in 12v fan heater on top of the inspection cover to demist/defrost his plastic screen and that set me thinking.


I didn't want wires trailing to the cig lighter as I thought that was a bit naff, but remembered that, of course, there is wiring already in place for the hardtop HRW. Could I make use of that? Course I could, not only that but If I got the switch and the relay it would look really neat.

SO:- I ordered a 12v fan heater (£9.99) and the mk2 HRW switch and relay(£20).
While waiting for these to arrive I studied where I wanted to fit the heater.

Sudden thought, if, rather than mounting it over the inspection cover, I mount it on the Tbar in front of the windstop and between the seats would it also act as a back of neck heater?

Well to cut it short the bits arrived and I stuck the heater temporarily in place and tried it. Hey presto, yes it would give some heat to your neck as well as demist the screen!!!

So I fitted it in permanently by removing the tbar and drilling three holes( scary) two for fixing bolts and one to feed the cable through. Fixed the heater in place and replaced the tbar after feeding the cable across to the HRW wiring. I spliced in a couple of connections (leaving the HRW plug in place - just in case we ever do chicken out and buy a hardtop).

Removing one of the switch blanks reveals the other end of the heated Rear window circuit. I simply plugged the hrw switch in and pushed the new switch into place in the dash, fitted the relay into the socket to the right of the under steering wheel fusebox (see pic below). With ignition on, press switch, ooh warm air!

On a frosty morning, I start the car, switch on the fan heater and after a while the screen starts to clear. The heaters are not exactly super hot, but I could definitely feel an improvement in the neck area whilst driving TOP DOWN today. Don't expect a fast demist, this is no way as good as a proper Heated rear window.

Had another MG badge so finished off the job by sticking it on the heater and here it is:-




The heater isn't volcano hot, but it does blow warmish air onto the window, and it does the job. The advantage of using the HRW circuit is that it also has a built in timer, so that the heater switches off after 20 minutes.
__________________When I bought the heated rear window switch and relay from Ebay, I was surprised that the relay was not a model specific or an MGR item , but just a common 40 amp auto relay, such as available at Maplins or Halfords.

I had bought a relay from Maplins for fitting some spotlights, and when my HRW one arrived they were identical! Only the one from maplins was only about £2.





Fitted in place and working fine.

Very resourceful and looks good in the photo
Does it affect the operation of the volumetric alarm since that is situated right behind the fan you've installed?

Anyway I digress, I stumbled across thread as I was thinking how to make an Air Scarf, like the newer Merc convertibles.

Your idea looks simpler, I was originally thinking of adding ducting to the existing heater and running it to blow warm air between the top of the seat and the head rest for both seats.

Has this ever been attempted?

The Merc system is, I think, an electric heater built in to the head rest which has fans on the back to blow cold air across a heating element.






Actually a pair of those seats would like very nice in a Tahiti Blue, white striped MGF

It didn't affect the volumetric alarm. I have now progressed to a glass window with integrated heating element.

The relay and switch work with the glass heated screen in the same way.

I've been planning an airscarf since i got my first F....would come in handy up here lol.

Never got round to it though.....but was thinking about some small ducting running under carpet under door then appearing at neck height...but I'm lazy lol

Sorry to open an old thread but just came across this in the How To section, one of these heaters that blows hot and cold would be a great addition, and it doesn't look out of place
I can feel a new project coming on

I would say that the heater pictured was not producing a great amount of heat.  More Luke warm.
Perhaps more modern versions are better.

i've been looking most are around 150w but there are some at 500w but obviously cost a lot more

Too hot would probably accelerate deterioration of the plastic window, to demist it shouldn't need a lot of heat, but I would imagine 150w at 12v of warmish air vaguely blowing in the general direction of the window, probably isn't going to be enough to archive much!

there are a few 200 and 250w they should be sufficient i would think

Alec wrote:

i've been looking most are around 150w but there are some at 500w but obviously cost a lot more

 500W is over 40amps!

These will be Chinese watts or What’s ? ? To calculate watts you multiply the value of the supply voltage by the current drawn by the circuit.
I’m not sure whether it’s the volts or the current which are devalued or if there is a different calculation used in the orient; let us settle on the Optimistic Watt or possibly the Over Optimistic Watt.
M