Morris Minor Owners Club

Can anyone tell me how to wire up a heated rear screen on a Traveller ? Bought a pair of rear glass for my mothers '1963' (it's her birthday) and I'm not too familiar with wiring that sort of thing. The car's been converted to negative earth but still has a dynamo ! Any advice would be great.

regards
Peter

Where did you get these windows? If it's from a Minor specialist then surely they should have given you all the wiring, switches & instructions to go with these rear screens? I would call them, unless of course you've obtained them from another source in which case using an auto electrician would be my personal choice for peace of mind. However I'm no expert on electrics and hopefully someone on here will be able to give a better answer.

Logically I would guess that the live wire should come from the ignition circuit so that you can't accidentally leave it on when you leave the car. It should also be fused. I'm sure a supplier of electrical components could supply switches with an appropriate time delay. As for the dynamo, they can only just cope with the lights, wipers and heater running in Winter so this new current hungry device might be a problem, especially if the car is used for many short trips.

If you aren't sure then an autoelectrician would be a good idea!

They should be powered via a decent relay to the battery (with a fuse that is the correct size to protect the wiring). The switching circuit should come from the ignition to ensure they can't be left on. The switch on the dash needs a bright light to warn you that they are on.
If you want to keep the dynamo I would recommend some clever device with a timer that turns of the switching circuit after 3 or 4 minutes, but even with that, you are likely to get the occasional flat battery in Winter for the reasons Chris already mentioned. It would be worth having a slightly higher duty battery and topping up with a battery charger every so often. (Really you should consider an Alternator)

Quite a few newer cars have timers on the heated windows. Some will have a separate box, others it will be in a multifunction controller. Unfortunately I don't know any off the top of my head that use a separate box, but my guess would be Mk1 Rover 200s and cars of that age.

Another alternative is to get (or get a friend to make) a voltage sensitive switch. Late 80's early 90's Range Rovers have these, a little yellow box used for exactly this purpose. If the voltage is a bit low they stop the heated rear window making things worse. They can also be used on split charge systems. Maybe you could find one in a scrappy.

Have you actually unpacked them to check for instructions, as most of them are supplied through the Birmingham centre, so spare instructions should be available, and as the others have said an Alternator is probably a must.

I've got the switch,relay,fuse,wire,little light to show it's on and terminals which I bought from a general motor spares, It didn't all come as a kit so there was no instructions.The dynamo is a bit of a worry but my mum wants to keep the car standard (yep I know a heated screen isn't standard) so an alternator is a bit of a no-no. Cheers for all the advice maybe an auto electrician is the answer.
Regards

Peter

ptr3500 wrote:I've got the switch,relay,fuse,wire,little light to show it's on and terminals which I bought from a general motor spares, It didn't all come as a kit so there was no instructions.The dynamo is a bit of a worry but my mum wants to keep the car standard (yep I know a heated screen isn't standard) so an alternator is a bit of a no-no. Cheers for all the advice maybe an auto electrician is the answer.
Regards

Peter

I have a dynamo in a box under my desk ... Should any subsequent owner wish to return mirium to her former glory .. They are welcome ...

I'd have to go with Ray on this one. Alternators are really the best option if you want to put a heated rear window in. Either that, or a way to power the heated window from an external source. I've never measured the output, but I know that heated rear windows draw a lot of current; you'll find a dynamo will really struggle to keep the battery charged...

The heated rear window kit I bought recently came with a wiring diagram which suggested an unfused circuit with a *big* switch (instead of a nice relay). Having uttered something similar to "there's no way on earth I would do that", although possibly less polite, I obtained a heated rear window relay, a nice small switch and indicator light and a fusebox (there's enough in-line fuses on my car now....).

Wiring wise (although I've not finished ) I took the power for the switch side of the circuit from the ignition controlled, fused positive; I just pinched this from somewhere under the dashboard ('cos I'm lazy and I've got my own extra instruments which means I already have a fused, switched +ve feed); this goes through my switch and to the relay (unfortunately, off the top of my head I can't remember which connection, but I think the relay connections are +ve -> 1; 30/51 -> Earth. I'd check that with a multimeter though

Then: A separate, beefy, unswitched unfused positive, to one side of your new shiny (probably 15-20Aish) fuse the other side of which goes to connection 87 (I think; one side of the relay anyway). The other side of the relay (85, I think), goes to one side of the heated rear window (presumably you have to run two big wires down, one for each pane of glass). The other side of the heated rear window(s) goes to earth.

Make sure your cable and connectors can carry a suitable current; there are lucar connections which will take up to about 20 amps; and you could stick an inline fuse in rather than an extra fusebox and put it somewhere nicely hidden. Apart from the actual window, in my saloon the only other changes I had to make were: I had to enlarge one hole (to allow a wire to pass through with a grommit) and will have to drill two holes to mount the relay; but I expect you could find some pre-existing holes to attach the relay to, oh, and I made up a little aluminium panel which hangs down under the dashboard to mount the switches on. At some point I'll make up a steel one now I know what it looks like; and I'll paint it to match the car

With a dynamo your mum is going to have to be a bit careful about when she uses it.....

Kate
Thanks, you've been a great help.

Relays rock... They are your friend. Not like the previous owner of my car, who had seen it fit to fit a heated rear-window which was switched without a relay, and had taken the power from the unfused side of the fuse box!!!

Pyoor_Kate wrote:(to allow a wire to pass through with a grommit)

Is it just me that's picturing "Electronics for Dogs" with those eyebrows above it?

Hello all,
I have been watching this thread and finally got round to doing a current measurement on my wife's Traveller's heated rear screen (Obtained from the Morris Minor Centre, B'ham). It draws 6 amps, so a load of 72 watts nominal.
If a switch of sufficient capacity is fitted then there is no real need for a relay. Switches are commonly rated at 10 amps with many rated for 20 amps. 14\0.30mm (1sqmm) cable is rated at nearly 9 amps but it would be better to use 28\0.30mm (2sqmm) cable to minimise voltage drop and so give more power at the rear screen.

Alec

Alec wrote:Hello all,
I have been watching this thread and finally got round to doing a current measurement on my wife's Traveller's heated rear screen (Obtained from the Morris Minor Centre, B'ham). It draws 6 amps, so a load of 72 watts nominal.
If a switch of sufficient capacity is fitted then there is no real need for a relay. Switches are commonly rated at 10 amps with many rated for 20 amps. 14\0.30mm (1sqmm) cable is rated at nearly 9 amps but it would be better to use 28\0.30mm (2sqmm) cable to minimise voltage drop and so give more power at the rear screen.

Alec

You are correct Alec, BUT For me a Relay is always a good idea. because rightly or wrongly I believe with a large resistive load that the initial current while it is cold is of comedy proportions and could burn out the contacts on a 10amp switch.

Justin

PS:- To the person who mentioned the Voltage sensitive relay. It's PERFECT for this application, I have one in the landrover and it controls all the heated parts and the split charge relay.

Hello Justin,

there is not that much of a surge when switching the rear screen heater, another check gives a reading of just over 2 ohms when cold and with i=v/r comes out at around my 6 amps running load.
I would imagine that the difference when switching headlights would be higher due to the very high difference between on/off filament temperatures but how many Classics have headlight relays as standard?

Alec

PS:- To the person who mentioned the Voltage sensitive relay. It's PERFECT for this application, I have one in the landrover and it controls all the heated parts and the split charge relay.

Does it still have the part number label? Starts with PRCxxxx. That might help if anyones looking in scrappy's or wants a shock when they ask a LR dealer for a price.

I have one on audrey for the split charge circuit and fridge in the 'van, but the part number label is missing.
Alternitavely, I probably still have the circuit diagram somewhere for anyone who can construct electronic circuits.

lowedb wrote: Does it still have the part number label? Starts with PRCxxxx. That might help if anyones looking in scrappy's or wants a shock when they ask a LR dealer for a price.

The landrover Mailing list is presently tearing itself to pieces over what the part number is. With a person claiming it does not exist at all

If it interests anyone here is the circuit diagram from the workshop manual. As soon as I get the part number I will post it.



Ignore the handwritten part that's the added parts for the front heated windscreen.

Oh, it definately exists. I had to modify the design to make it suitable for the 24v military versions so I ought to know.
If I can find a copy of the circuit, I might just have the part number on that.

Any chance of a bit smaller picture

Found it. Part numbere is:

PRC4427