Heated rear window wiring

[mgcjag]

Hi All.....there has been some confusion on the HRW circuit. I have linked it here for interest viewtopic.php?t=7447

[vikla]

Hi Steve

My comments in the original thread were based on the Forum thread you referenced which showed a wiring diagram which I believe is the so called S1.5 version in the Knowledge Base.
Here is the HRW detail:

This would appear to be the conventional use of a 6RA relay as I described. C2 and C1 are normally open and close when W1 is energised.

The other S1 diagrams are different from the above, one of them is:


These show a different version of the relay where C3 and C2 are normally closed contacts and will open when W1 is energised.
I can now see how it would operate as you suggest in the previous post if there was an internal resistor in the relay from W1 to C3.

In the two wiring versions the main feed to the HRW comes from different sources.

Some questions for anyone to answer:

- it still does not address the issue that started the previous thread, that in the guy's S2 his HRW does not come on unless the lights are switched on. This would appear to be as per the S1.5 scenario. BTW, I couldn't find a S2 wiring diagram with the HRW on it.

- What is the resistance or wattage of the HRW, which can tell us how much current it draws? The inline fuse is only 15A which seems rather low to me, certainly for a modern HRW.

- Did Jaguar modify the circuit some time so that both different circuits were used over a period.

[mgcjag]

Hi Steve your second diagram is the same as the jaguar diagram in my S2 operation and maintenance handbook.....the small buff colour one.....it also has the inline fuse rated as 15amp.....however with modern fuses this value is altered...see link for fuse ratings viewtopic.php?t=3102&highlight=fuse+blow+rating
tried to get a diagram of the internal Cct of the relay but no luck (6ra 33265 or C26651) Although i refered to it I cannot find the first diagram as above in the jaguar manual, all the Ccts are as per the 2nd diagram above I cannot see the first being correct as you would need the light switch on the operate the HRW which cannot be right...... Steve

[chrisvine]

I think Christopher's point in the top link is good advice and the diagrams are probably suspect. The W terminals are for the control circuit which switches the power circuit, connected to the C terminals.

Therefore the dash switch should be controlling the supply to W1 as in the first diagram. I agree taking the C1 supply from the Red fuse 5 is wrong, since it introduces a second switch into the equation.

Wiring to the supply (White) controlled by the ignition switch as suggested ought to provide the result you're probably looking for?

[jcarey]

Hi Steve your second diagram is the same as the jaguar diagram in my S2 operation and maintenance handbook.....the small buff colour one.....it also has the inline fuse rated as 15amp.....however with modern fuses this value is altered...see link for fuse ratings http://forum.etypeuk.com/viewtopic.php? ... low+rating
tried to get a diagram of the internal Cct of the relay but no luck (6ra 33265 or C26651) Although i refered to it I cannot find the first diagram as above in the jaguar manual, all the Ccts are as per the 2nd diagram above I cannot see the first being correct as you would need the light switch on the operate the HRW which cannot be right...... Steve

Steve,
I know this is a while ago, but I found the internal relay circuit in Service Bulletin # P.49 which announced the "Incorporation of Control Switch In Electrical Circuit for Heated Back Lights." See the attached diagram.

[mgcjag]

Hi John....yes the diagram shows that when the heated rear window is switched on the warning lamp glows....the relay is there for one function...to dim the warning lamp when the side lights are on....thanks for posting.. Steve

[MT2+2]

Hello all,

Can any of you advice me on how to fix my HRW, which is very feeble at the moment?

Thanks to this and the original posts, I have established that all seems to be well with the HRW switch, relay, and wiring up to the rear door, where I get a healthy 12.3v.

However the resistance from the bullet connectors onward through the element is about 95 ohms. So my school physics tells me that its only providing about 2watts of heat!

Prime suspect is the connection of the wires to the element at the edge of the screen, the question is how best to get at them? Will I have to have a professional to remove the screen, or can I cut or peel back the seal in some way to gain access? The seals are only a couple of years old and Im wondering if the connctions were damaged at that time by the fitter.

My car is a 1966 Series 1, 2+2 which has the original vertical heating element fitted.

I would also like to thank all the contributors to this and the origanl post, which saved me many hours of frutless work, and enlightened me on how the 6RA is used in this unusual case. Mine actualy dims the warning light!

Best regards
Martin Thomas

[MarekH]

It sounds as though very few of the strips are connected and damage during fitting sounds like the obvious cause. If you turn it on now, you may deduce which ones are broken as they will contribute no useful heating effect.

Conductive paint can be used as a fix. As the strips are all in parallel, the resistance will plummet as they get reconnected.

The relay arrangement is most bizarre - I was most surprised that it simply connects the warning light with a lower voltage than 12v. It is a truly expensive and stupid way of achieving very little of value.

kind regards
Marek

[MT2+2]

Hi Marek and thanks for your reply.
I persuaded a local windscreen fitter to take a look at the HRW today, and they tested it with a bowl of hot water under the window. This showed that some of the elements are working, and many not, and their conclusion was that the elements themselves have deteriorated over the 50m years rather then the wire connections at the screen edge. They may be right, so I have decided against having the screen removed at the moment, due to possible wasted cost and effort. I think the best thing to do is to sit tight until I can find more definitiave evidence one way or the other.
One beneift of fiddling around with the rubber seals was that the resistance of the element has now dropped to about 30 ohms, so its working better that it was!
Best regards
Martin

[Gfhug]

Martin

My heating wires run across not vertically in the window. It was not working due to a disconnect on the earth side of the element at the window. Instead of the hassle of removing the window to make good where it was faulty I ran a new wire which is both glued and held in place by the seal. Crude, but it has done the job and means I have a working HRW.
The photo will show both the elements and the new (white) wire to earth tucked under the seal. It will also show how the elements run.
Don't know if it can help for your setup:


Geoff

[MT2+2]

Thanks for photo Geoff. I attach a couple of similar shots of my window although Im not sure if it will help much! The white strands on the screen are just dust.
Having tried the HRW again today and found it wanting, Im inclined to get the window out for a thorough nspection as a winter job.
Best regards
Martin

[Gfhug]

Martin, I'm guessing and only guessing. But if they are fine wire elements sandwiched in the screen is there a copper strip pressing against the edge of the screen to give the circuit? If so, when you come to take the screen out it may be a case of having to get that to make good contact with the wire elements.
Without seeing it up close then it is only a guess as to how the circuit is made. Poor contacts giving high resistance and open circuit?

Keep us posted when you get to do the work.

Geoff

[mgcjag]

Hi Martin....please try to put your name and car model in the signature line........have you tried opening up the rubber seal on the inside...use some wooden pegs to seperate the rubber from the glass...you will get a better view and accses to test whats going on......i have taken out and put back in a rear screen it wasnt that difficult but takes two.....Steve..

[Reno001]

Hello,

I hope it is OK that I post in this topic because I have a similar problem and I did not want open e new topic. One of my winter jobs is to repair the wiring of my heated rear window. I read in the Workshop Book that it gave two methods to connect the window.

Method 1: window with vertical heating coils over the lower hinge and the cavity of the door to the connectors on the bottom of the window
Method 2: window with horizontal heating coils over the upper hinge directly to the connectors on the side of the window.

In my case I found the wire disconected in the cavity from the rear door but I have a window with horizontal heating coils. So I changed the position of the wire from the lower hinge to the upper hinge. Now I have no idea how to bring the wire to the connectors. Perhaps somebody drives a Series 3 Coupé with a heated rear window and horizontal coils to send me a photo of the wiring from this area?

Thank you very much for help.

best regards

Reno