Heated Windscreen

[Mark_Solesbury]

My 90 has a heated windscreen. It never really worked well, but was replaced a month or so ago after a massive chip.

So its now got a brand new one in it.

This morning, it was slightly steamed up on the inside. Turned the heated screen on and it did not clear.

The engine note changed as expected from the extra load.

It has 3 wires to it. Negative on each end, and a positive in the middle, and is fed from one relay behind the speedo.

Id this wired up correctly? The screen was on for a good 5 mins, and nothing happened - by this time the heater had warmed up so i used that to clear it.

Id really like to get this working!!

[L90OOK]

I'd say you have wired it wrong.  Should be +'ve on each end & -'ve in the middle.  8)

[Bush Tucker Man]

Try this article by Ross Floyd

[Darren]

I asked a similar question a couple of weeks ago as mine has one that's neer been wired up. You can read the very helpful responses here including a link to an excellent wiring diagram.

[Mark_Solesbury]

Right.

Its frosty here this morning, so i thought id investigate.

It is wired up correctly, but its only getting 11 volts the terminals. It does clear a bit, but its not very good.

The alternator is kicking out 14 volts, and thats what i get from measuring across the battery terminals.

I am gonna re-wire it later tonight, with a large cable from the battery though a big relay (75A?) and take a switch wire from the existing heated rear window. Ill wang an inline fuse somewhere. Any suggestions on size?

I assume that the poor performance is due to the low voltage getting to the screen??

[Bush Tucker Man]

I assume that the poor performance is due to the low voltage getting to the screen??

Is the cable 'man enough' to handle the current??

[Mark_Solesbury]

Probably not, which is why im gonna get some proper stuff at lunch time.

Any recommendation's on girth?

[L90OOK]

Some decent 27.5 Amp wire should be good enough.
Make sure you have a good crimp tool too.  Don't use the scotch blocks for jumping wires...wire it properly!!
If you can get some heatshrink terminals I'd use them...I know how wet the inside of the windscreen can get!  :shock:
You may well be overloading your switch if you are running your rear & front screen from it...wire in a quality second switch for the front screen.



From CROYTECH

[Litch]

Yep, sounds to me like it has been wired in with whatever was to hand at the time instead of the correct gauge wire and therefore you are suffering quite a lot of volt-drop.
I seem to recall when I did mine that the current draw is something in the region of 30A (can't remember if that is each side or combined) so don't assume that the same stuff you wire a radio or spot-light up with is going to do the job.
The correct sized cable & switchgear are essential to make it work correctly, don't tee into existing circuits unless it is only for the control side of the relay.

[Mark_Solesbury]

Plan is to attack it at the weekend.

Thing is - Whats the best way to split it to the 2 +ve's on the screen?

Run Straight from battery (via fuse) to Relay. Out from Relay with 2 cables to  each terminal on screen using a 12v feed to switch?

Or do 2 runs with 2 relays that can share an earth and a switch.

[Elmo]

Given the price of relays I'd use the second option and then you can wire the lot in 30A cable, otherwise you'll need a 60A feed and relay. Fuse each side and then if the damp pixies get in you may not lose both sides.

If you've already got a big relay and cable.....either :)

[Darren]

The factory arrangement uses one large 70 amp relay :shock:

[Litch]

Personally I used two 45A relays fed from two separate fuses on the aux fusebox and one control switch (VWP sell switches with all the correct symbols on). The cost difference is negligable and I always like to over-engineer.
When working properly you should find it demists within 2-minutes of turning on and a good covering of ice will start to melt soon after.

Unless you are certain you will always remember to turn it off consider using a timer relay. I believe that OE spec is to only allow the relay to operate when the oil-pressure light has gone out (this confirms that the engine is running and you are not going to rapidly drain your battery) but can anyone confirm this is correct?

[L90OOK]

Plan is to attack it at the weekend.

Thing is - Whats the best way to split it to the 2 +ve's on the screen?

Run Straight from battery (via fuse) to Relay. Out from Relay with 2 cables to  each terminal on screen using a 12v feed to switch?

Or do 2 runs with 2 relays that can share an earth and a switch.

You can get all the relays, connectors, wire etc... from Vehicle Wiring Products.
I have used them a few times & always delivered fast & reasonable prices.

[muck_truck]

You can get all the relays, connectors, wire etc... from Vehicle Wiring Products.
I have used them a few times & always delivered fast & reasonable prices.

its a bit like a sweet shop their online store!  i went on today to order some relays and switches for the heated seats i just fitted to my 90 and the order ended up at £124!!!

[L90OOK]

You can get all the relays, connectors, wire etc... from Vehicle Wiring Products.
I have used them a few times & always delivered fast & reasonable prices.

its a bit like a sweet shop their online store!  i went on today to order some relays and switches for the heated seats i just fitted to my 90 and the order ended up at £124!!!

Yup  :roll: ...you need to be real disciplined to use the online store...bit like going to the Devon 4x4 online shop  #-o  ](*,)  :smack:  :lol:

[Elmo]

Heh just been to D44 and been naughty with the plastic.... and I could have been naughtier!

Auto Electric Supplies are good too, smaller range but until recently VWP did not do online ordering and AES did, which at 2AM is an advantage ;)