Heated rear window fault

[Zaphod]

Now I have my Excel on the road and m driving it a number of faults have come to light, one or them is that the heated rear window does not work. The light in the button for it comes on as expected but no effect on the rear window. However if I use the horn while the heated rear window is on the horn also does not work but the 20 amp fuse for it blows, Horn woks fine when the heated rear window is not on (and the fuse is not blown). This seems a bit odd as the 20 amp fuse only blowing when he HRW is on would indicate the switch for the HRW is supplying something.
I also have a very unstable fuel gauge, and have read about a mythical 'anti slosh' relay but no mention of it in the service notes, is it a myth or part of the red fuel level relay that looks far to big to be just a relay!

[Zag]

Isn't the anti slosh is for light only not gauge. I swapped my gauge and Found it now swings rather than spikes around.

[Alan_M]

The anti slosh relay is normally next to the fuel tank behind the boot trim panel. I believe it damps the signal for both the needle and light. Most are no longer working, but if it bothers you an alternative is to fit one of these - https://spiyda.com/fuel-gauge-wizard-mk3.html

[Zaphod]

I seem to recall another post mentioning that location, however I can't find it in any of the circuit diagrams? However the diagram does show a low fuel level relay which I have found under the instrument cluster, its a red one with a lotus sticker on it.
Has anyone looked in common causes of failure of the anti slosh relay? I may have to take a look at it if I can find it!

[Zag]

Just checked the wiring diagram and for an 86my the anti slosh relay is only for the light (Section md sheet 4) Don't know about other years .

[Zag]

Section md sheet 30 shows its location to be next to the fuel tank on the near side. Its description is low kevel tell tale relay, further reinforcing that it has nothing to do with the gauge.

[Zag]

I presume it's fuse 24 that blows. Does it blow when the fog lights are on and you press the horn? The hrs circuit it very simple however if the rear screen element has gone bad i don't know what your options would be. Have you checked for 12v at fuse 1? That should tell you if there is a switch / relay issue or an element problem.

[tonypoll]

I fitted the Spiyda anti-slosh circuit some years ago, and it works very well. The fuel gauge no longer leaps around.
However, don't fit it next to, and take the electrical feed from, the fuel pump. If you do this the fuel gauge will jump every time the fuel pump 'ticks'.
I fitted mine (the second time, after my first attempt was next to the fuel pump) behind the instrument cluster. It's now just fine .

[MetBlue]

However, don't fit it next to, and take the electrical feed from, the fuel pump. If you do this the fuel gauge will jump every time the fuel pump 'ticks'.
I fitted mine (the second time, after my first attempt was next to the fuel pump) behind the instrument cluster. It's now just fine .

Thanks interesting and useful to know.
I bought the Spiyda unit a couple of years back but haven't yet fitted. When I have come close to fitting, I'd been tempted by a more accessible location than behind the instruments. Maybe not now.

[Hawaiis0]

The leads to the window are easy enough to access. Pull them off the try the switch toman see if the fuse blows.

[rbgosling]

I've had exactly the same problem with the rear screen demister.

The issue is that there are two fuses involved in the system.

• The first fuse is a low-rated one, 2A I think, which just protects the switch side of the circuit. It also protects the switch side for the horn, and one or two other switches, possibly the heater fan IIRC.
• The second fuse is higher-rated, and protects the circuit that actually supplies power to the rear screen demister.
• These fuses live either side of the relay (in terms of the electrical circuit diagram, not their physical position!)

When you press the demister switch, a short-circuit is being created that blows the 2A fuse, thereby denying power to the horn switch and other switches on that circuit. The problem therefore is not in the demister itself - that's the far side of the relay - it's in the switch circuit.

I'll give you 5:1 odds that, if you track down the relay for the demister, remove it and take off the cover, it'll be rusty inside and quite possibly full of water. Any slight leak from the windscreen tracks down to the relay bank by your right knee, and because they are mounted upside down water can get in and fill up inside the relays. When you press the demister switch, it sends a live to the relay, and the rust/water results in a short-circuit and blows the fuse.

If I'm right, when you replace the relay, I'd suggest drilling a small hole in the cover so if water does get in, at least it can drain out again.

[Tanz]

A bit like this

[hodders]

Or this:

[Zaphod]

I fitted the Spiyda anti-slosh circuit some years ago, and it works very well. The fuel gauge no longer leaps around.
However, don't fit it next to, and take the electrical feed from, the fuel pump. If you do this the fuel gauge will jump every time the fuel pump 'ticks'.
I fitted mine (the second time, after my first attempt was next to the fuel pump) behind the instrument cluster. It's now just fine .

I actually have two of those, one in my MGA and the other in the Midget!

[Zaphod]

Section md sheet 30 shows its location to be next to the fuel tank on the near side. Its description is low kevel tell tale relay, further reinforcing that it has nothing to do with the gauge.

My car is a post 89 car, and is the next section of electrical diagrams