Heated rear window - re-wire

[AlfaJack]

I would like to rewire the heated rear window and get rid of that box of tricks that houses the radio amp too.
I heard it burn out this morning as I think it got damp from where I had left the boot rest resting down rather than shut for the last 5 days

This is about the 3rd box it is on too due to the previous 2 breaking.

How could it be done so I don't need the box?
I think there are two skinny wires that come in from a relay in the fuse box to the amp under the parcel shelf and then 2 fat wires out to the window.

What does the box actually do? Does it ramp up the ampage somehow?

I have a roof aerial too for the radio so not bothered about that.

Cheers,
Jack

[Steve Webb]

If you take the aerial out of the equation, then the box in the boot should just contain a relay for the rear demister.
The rear window will require quite a lot of current, the relay is there so you don't need to run this current through the demister switch.
As the box has died on you, I'd open it up take a look for the relay, and try to read the numbers off the top of it. Should give you an idea as to what size relay you need. Then just go out and get a generic relay and wire it in.

[AlfaJack]

If you take the aerial out of the equation, then the box in the boot should just contain a relay for the rear demister.
The rear window will require quite a lot of current, the relay is there so you don't need to run this current through the demister switch.
As the box has died on you, I'd open it up take a look for the relay, and try to read the numbers off the top of it. Should give you an idea as to what size relay you need. Then just go out and get a generic relay and wire it in.

I don't think there is a relay as there is already one in the normal fuse box..

[Steve Webb]

In which case the only possible reason for the box is to tap into the rear screen circuit to gain access to the radio signals.
You might be able to bypass the box completely and just join the wires entering the box to the ones leaving.
Although before doing that you might want to make sure that the wires do go where you think they go.

When you said you heard it burn out this morning, how loud was it?

[AlfaJack]

In which case the only possible reason for the box is to tap into the rear screen circuit to gain access to the radio signals.
You might be able to bypass the box completely and just join the wires entering the box to the ones leaving.
Although before doing that you might want to make sure that the wires do go where you think they go.

When you said you heard it burn out this morning, how loud was it?

It sounded like an electrical sizzle - not too loud but I am pretty sure I know what it was.

[Steve Webb]

I've just had a look through the manuals, and there is nothing in there past how to remove the box, which seeing as you've had 2 die on you already , is pretty useless.

So after it went 'sizzle' this morning did the rear screen demister stop working?

[AlfaJack]

I've just had a look through the manuals, and there is nothing in there past how to remove the box, which seeing as you've had 2 die on you already , is pretty useless.

So after it went 'sizzle' this morning did the rear screen demister stop working?

I wasn't brave enough to leave it switched on - it happened within moments (I think) of switching it on though.

[Steve Webb]

Just a thought, but have you checked you haven't got a short in one of the wires going up to the screen have you?
Seems odd that you are getting through so many aerial amps.

[AlfaJack]

Just a thought, but have you checked you haven't got a short in one of the wires going up to the screen have you?
Seems odd that you are getting through so many aerial amps.

I don't think so. I will check though.

The first one I had just didn't seem to work and I can't remember why. The next I think I may have damaged it when installing as the wires came away from the circuit board and didn't solder back very well.
The third is the current one and yet to investigate...