One for the electricians

Jamieg285 · December 22, 2006, 04:50:31 AM

What do I need/how can I wire up a heated rear screen?

Make the assumption that all I have is the rear screen, with none of the stock wiring/switches - I want to do this from scratch.

Titsy · December 22, 2006, 05:38:39 AM

Firstly you need to know how much current it is going to pull so that you can select the correct gauge of wire and switch (depending upon this you may also want to fit a relay, and will certainly want to fit a fuse)...

The easiest way to check this is to measure the resistance across the element and then use this to calculate how much current it will draw as follows:

V/R = I

Where:
V is the maximum system voltage (usually around 14.3v for a 12v system),
R is the measured resistance, and
I is the current that will be drawn by the element.

Be careful with your units when measuring the resistance...

Shout when you get this far...

The way in which is it wired from there is largly dependant on how much current you will be drawing, but it is really as simple as providing a permanent chassis ground to one side, and a switched 12v feed to the other...

Jamieg285 · December 22, 2006, 05:45:45 AM

I'm with you on all that stuff (not sure exactly how I'm going to measure the resistance yet, but I'll take a look at my multimeter and see what it can do)

I was thing more about how to wire in relays/timers, and what sort of switch. At the moment is a 3 way - 'trigger on' - 'trigger off' and 'middle'. Not sure if I need to find a similar switch, or if a simple on/off, or single trigger/off will do?

sixpack2639 · December 22, 2006, 10:33:12 AM

Jamie, I know you said assume all you had is the windscreen but my Olds has the same system yours does so what exactly in wrong with yours as I may be able to help you with it. Carl

Jamieg285 · December 22, 2006, 01:23:35 PM

Quoting: sixpack2639

Jamie, I know you said assume all you had is the windscreen but my Olds has the same system yours does so what exactly in wrong with yours as I may be able to help you with it. Carl

The switch is old and grubby and may not clean up very well. I was thinking of replacing it with a totally different switch, but not knowing what is contained within the switch, I thought it better to replace the whole lot.

sixpack2639 · December 22, 2006, 02:23:46 PM

It's a rocker type switch that always returns to the neutral position.

I believe it does have a timer of sorts or possibly a heat sink built in so it won't overheat.

I would try taking it apart just enough to get to the contacts inside and clean them up then it should go back to working just fine.

I actually need to do the same thing with mine as sometimes I have to hit the button several times before it turns on.

I would NOT try to put a toggle switch in to replace it.

If you're not in a big hurry and can give me a day or two, I have a complete set of factory manuals including parts manuals, I can go through them and maybe get some more insight as to how complicated the switch actually is and may even have a diagram or exploded view of the switch I can scan for you.

F Body · December 23, 2006, 02:16:02 PM

Quoting: Jamieg285

all I have is the rear screen, with none of the stock wiring/switches

Hell I love classics but I can't think about a daily driver without a heated rear screen in winter !

Respect Mr G your hardcore

sixpack2639 · December 24, 2006, 01:39:06 AM

Jamie has the whole system Martyn, it's just not in proper working order. Apparently his switch for turning it on and off is daft.

I'll be pulling me books out tomorrow (later today actually) Jamie, as I have actually caught up with Christmas and will have a few moments to spare. Carl

55starchief · December 24, 2006, 08:06:48 AM

If it is just the switch i would look on ebay for a NOS one and replace it, infact its gonna be the same as the one on a pontiac, i can take a look on the T/A as we wont need it or haver a look on http://www.pontiacparts.net\" target=\"_blank\" rel=\"nofollow\">www.pontiacparts.net and see if they have one listed they have one of the largest parts inventories i know of and are real nice guys

sixpack2639 · December 25, 2006, 04:10:22 PM

Jamie, you got mail. Sorry it took me so long mate.

As usual, I thought I was caught up but management told me different!

I emailed the schematic to you rather than post it due to copyrights, don't want to get Admin in hot water and all.

After looking at it i'm thinking there may be a problem with your relay/timer rather than the switch, but also see you could use a rocker type toggle switch to replace the original as the timer is not in the switch.

Hope it helps.

Cheers, Carl.

Jamieg285 · December 29, 2006, 04:40:43 AM

Quoting: F Body

Quoting: Jamieg285
all I have is the rear screen, with none of the stock wiring/switches

Hell I love classics but I can't think about a daily driver without a heated rear screen in winter !

Respect Mr G your hardcore

It does work (of sorts). The switch is tempremental, but does turn the thing on/off with perseverence. When on, the screen causes interference with the radio!. Only half the lines work.

The whole system needs sorting really.

Jamieg285 · December 29, 2006, 04:42:10 AM

Quoting: 55starchief

If it is just the switch i would look on ebay for a NOS one and replace it, infact its gonna be the same as the one on a pontiac, i can take a look on the T/A as we wont need it or haver a look on http://www.pontiacparts.net\" target=\"_blank\" rel=\"nofollow\">www.pontiacparts.net and see if they have one listed they have one of the largest parts inventories i know of and are real nice guys

I've looked for NOS before, but they are very hard to find. Yes, it might be possible, but at what price and how long would I have to wait?

I figured being as I am 'updating' some of the other stuff in the car, why noe this switch?

Jamieg285 · December 29, 2006, 04:44:46 AM

Quoting: sixpack2639

Jamie, you got mail. Sorry it took me so long mate.

As usual, I thought I was caught up but management told me different!

I emailed the schematic to you rather than post it due to copyrights, don't want to get Admin in hot water and all.

After looking at it i'm thinking there may be a problem with your relay/timer rather than the switch, but also see you could use a rocker type toggle switch to replace the original as the timer is not in the switch.

Hope it helps.

Cheers, Carl.

Thanks for that Carl. I think I have seen the relay that it shows, so I think I will trace the wires and see if it is the one.

It's not just the action of the switch that annoys me, its the actual condition. The black has greyed with age (in a non-uniform manner), the white bits have also partially faded. I reckon it could be painted, but won't look as good as a shiny new switch.

sixpack2639 · December 29, 2006, 11:55:48 AM

If you pull out the switch there should be a part number moulded into the plastic on it somewhere. Then try looking here http://www.automobilearchives.com/part_number.asp\" target=\"_blank\" rel=\"nofollow\">http://www.automobilearchives.com/part_number.asp . They may actually have a NOS one.

Cheers, Carl

Jamieg285 · December 29, 2006, 12:04:36 PM

Quoting: sixpack2639

If you pull out the switch there should be a part number moulded into the plastic on it somewhere. Then try looking here http://www.automobilearchives.com/part_number.asp\" target=\"_blank\" rel=\"nofollow\">http://www.automobilearchives.com/part_number.asp . They may actually have a NOS one.

Cheers, Carl

Cool. I'll give that a try.

55starchief · December 29, 2006, 12:12:07 PM

i will have a look and see if the t/a has one if so could do a swap