I bought a 1991 MK1 Eunos in the summer which had a recenbtly new ‘Autohoods’ mohair hood with glass heated screen. The switch is to the right of the steering column but has never worked. I haven’t bothered up to now to investigate the problem, but in the last couple of weeks there have been occasions when a heated rear screen would have been useful so I took a look this afternoon.
I established there was a live supply to the switch with the ignition on and the continuity of the wiring back to the screen is fine. I then lifted the carpet beneath the screen where the two wires disappeared under the hood and found one of the ends bound with insulating tape and not earthed to the body. It would appear a simple matter just to fix this wire to one of the bolts to provide an earth to make the heated rear window operational. However there does not appear to be a relay anywhere in the circuit and I am concerned this may cause the wiring under the dash to overheat.
Can anyone advise if a relay is essential in this case and if so how it is best fitted? I am further concerned that the live supply appears to have been spurred off the rear fog light switch which is next to the heated rear window switch in the dash. I am therefore assuming this does not have a relay either!
Early cars don’t have the HRW wiring fitted from the factory. Do you have the 3 pin plug on the LH seatbelt tower? Assuming you do…
The HRW switch, fuse block & relay were not fitted at the factory for NA. These components were fitted to the vehicles as & when hardtops were installed. The switch you have obviously found, the fuse if fitted is in a small twin fuse bock in the boot mounted near the base of the aerial & the relay should have been mounted to a stud behind the rear internal boot trim near the boot lock mechanism. It should be plugged into a 4 pin black & yellow plug. Have a check & see which of these components you do or don’t have.
edited… just re-read your post. Am I correct in thinking that the wiring for the HRW has been added? In that case, yes you would need a relay.
Had a good look around the boot and tower and cannot find the any signs of a relay or fuses. Although there is wiring to the HRW at present this has been run straight from the switch, where tthere is a live supply, by feeding the a wire under the carpet and up through the centre consol. I am therefore pretty sure there is no relay and the power load would therefore going straight through the switch if I earthed the other end. I assume from what you say this is really unacceptable and the circuit should be controlled by a relay. I this is the case how should I go about wiring this? As I said before it looks as if the supply has taken form the adjacent rear fog light switch so am assuming this may need a relay as well.
Yes you really do need a relay. What do you know already about wiring a relay & relay’s in general? To describe the whole wiring up a HRW in text could go on for ages & get complicated. May I suggest a read though a specialist Haynes manual like the one in the link or doing a quick google search then you could ask more specific questions.
Hi. I’ve just registered as a member since I’m trying to solve a similar problem on my wife’s Mk1 Eunos. We also had a new mohair roof & glass rear window fitted earlier in the year but the heated screen has never worked. I’ve established that there is power at one of the 4 wires on the terminal block at the rear of the switch but theres no power reaching the rear screen. I’ve removed the switch and put a meter across the terminals to test for continuity with the switch in the on position, but there’s none so my first impression is that the switch may be faulty. I was tempted to “short” the live & switch live to see if this confirms it, but I don’t know which one of the 3 remaining wires goes where. I’m assuming that one goes to the dash, but I must admit auto electrics always seem far more complicated than they probably are. Any suggestions would be really appreciated.
Many thanks,
Alan.
Alan, what age car is it? Ideally can you post your VIN? Does your car have the factory wiring for the HRW (a 3 pin black plug on a metal bracket on the passenger side of the parcel shelf)? Are the relay & fuse block in place?
You should be able to establish which wire is connected to the HRW by using your meter with a probe on one of the connectors at the switch and the other on the terminal on the HRW glass, whhich is soldered on mine and testing the continuity.Providing the ignition is switch off none of the wires should be live.
Thanks for both the very quick answers. The testing reply would seem to make sense, not sure why i didn’t think of it myself! As for the other, its an L plate, with the 3 pin connector on the parcel shelf (again, 2 neutrals, both joined together & one live, why is this neccesary?). The fuse is in a small block very close to the battery. I haven’t got as far as the relay yet. Am I correct in thinking that the switch connects directly to the relay, which in turn provides the power to the screen, allowing the heater to draw a higher current than the switch would be able to cope with? Please forgive the novice questions, the last time I looked at car electrics was on a Mk3 Cortina long before cars became complicated. I’m enjoying the fact that this might be a car that I can start getting my hands dirty with!
Regards, Al.
You should have a live at the Blue/Red (L/R) wire at the switch. This live is from the coil side of the defroster relay which is powered from the 20A WIPER fuse (arrives at the relay on a Blue (L) wire. The Violet (V) wire at the switch goes to the plug on the rear shelf and is grounded by the looped black wires when the defroster is plugged in. With the switch closed, the defroster relay puts 12V down the Red/White (R/W) wire to the plug on the shelf. The relay is fed from the Red ® wire from the 10A DEFOG fuse in the boot. The fuse block is directly fed from the battery. The Red/Black (R/B) & the Red ® wires at the switch are for the switch night time illumination (the R/B being live with the side lights on).
Hi. Thanks for the replies. It’s the weekend again so I’m back on the job and it seems that this was down to loose connections the parcel shelf block!! Thanks again, you’ve all been a great help.
Regards, Al.
My 1991 Roadster also had an Autohoods roof with glass heated rear window fitted when I bought it. It also did not work but I traced it to the relay. It is located in the boot,behind the carpet trim by the boot latch/number plate area. This is the part http://www.mx5parts.co.uk/product_info.php/products_id/174
Here is how my plug is wired. As you can see the bottom terminal is linked to one of the top ones.
This has been a lot of help as I am struggling to find any info on the switch wiring for the heated rear window switch anywhere online. I have been fixing the wiring behind the dash as it has been butchered at some point in the past with many wires snipped and spliced. Thanks.
Still have a couple of questions, though, if someone can help. In my tinkering a found a switch dangling which I have since found out is the heated rear window switch. One of the wires was snipped so close (6, in diagram below) I can only guess the colour. My switch has the following pin layout
1 2 3 4
5 _ _ 6
It’s wired as follows:
1 - Violet
2 - Blue/Red
3 - Green/Yellow
4 - Red/Black
5 - Red/Black
6 - Red (I think)
If this is, indeed, the heated rear window switch - which going by your description of colours and location above, it must be - what are the other wires for? Are the two red/blacks different?
Sorry to reopen the debate on Mark 1 HRW but I’ve just acquired a really good Mark 1 (MX5 - UK car) with a glass window that has never been wired up. I’ve scoured the boot and all the suggested places for factory wiring but there is no fuse panel or relay in the boot and no connector adjacent to the seat belt tower. Does this mean that there is no provision in the factory harness at all for an HRW connection? I have obtained the necessary Mazda parts (switch, relay, fuse box) but am now wondering if I will find a connector for the switch under the dash board. If it is there, where do the relevant connectors appear in other parts of the harness as I can see no unused plugs in the boot area?
