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Old 02-16-2015, 11:46 PM   #1
supremekizzle
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Join Date: Aug 2014
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2005 Saab 92x
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Default Need a wiring wizard, electrical genius for foot well lighting.

So, I've decided to do foot well lighting in a 2005 92x. I know how to do the basic install, but I'm looking for something a bit more custom and was hoping a resident electrical magician could help me with the wiring. Basically, I'm going to tie into the dome light so it will come on with the doors, but I also want to install a switch next to the fogs that will turn them on and want the switch to also turn on the dome light. Every car I've ever had has had a switch near the steering column that would turn on all interior lights and it was very convenient when you wanted to find something to just hit the switch. If I tied into the dome light, would turning the dome light switch turn on the footwells? If so, theoretically all that I should have to do is run a wire parallel down to the steering column to a switch, right? Any help would be appreciated. Especially appreciated would be a drawing showing the circuit I'd have to make. Thanks!
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Old 02-17-2015, 09:21 AM   #2
Cougar4
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If the Saab system is similar to the Subaru design then power is applied to the dome light at all times, the ground return side is switched to turn on the light with switches inside the door frame. You have the right idea to connect things up. Running wires across the dome light to the foot well lights and a switch will work. Pull the fuse to the dome light circuit before you work on it in case something shorts. Run the power side of the dome light to the one side of the new lights then tie the other side of the new lights to one of the switch contacts. Also tie a wire from the return (ground) side of the dome light to that same switch contact. Then tie the other side of the switch contact to ground. Replace the fuse and you should now be able to turn on all the interior lights with your new switch.
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Old 02-19-2015, 12:53 AM   #3
supremekizzle
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Quote:
Originally Posted by Cougar4 View Post
If the Saab system is similar to the Subaru design then power is applied to the dome light at all times, the ground return side is switched to turn on the light with switches inside the door frame. You have the right idea to connect things up. Running wires across the dome light to the foot well lights and a switch will work. Pull the fuse to the dome light circuit before you work on it in case something shorts. Run the power side of the dome light to the one side of the new lights then tie the other side of the new lights to one of the switch contacts. Also tie a wire from the return (ground) side of the dome light to that same switch contact. Then tie the other side of the switch contact to ground. Replace the fuse and you should now be able to turn on all the interior lights with your new switch.
Thanks for the reply. Would the dome light switch still function independently if needed with this set up? Thank you


Edit: Nevermind. It will because the electricity will follow the ground created by the dome light switch to complete the circuit or it will follow the path made by my custom switch. I think that sounds right. Both should work independently of one another. I actually might add in even another switch so I can have just the foot well lights on independently as well. I actually love car wiring...I just wish I knew it better...

Last edited by supremekizzle; 02-19-2015 at 02:17 AM.
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Old 02-19-2015, 12:05 PM   #4
Cougar4
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Your logic is correct. The two switches will work independently because they are in parallel with each other and the load is in series with the two switches. You could use a single ON-OFF-ON switch to do what you want to do with just the foot well lights. Tie ground to the center common contact and the light wires to the other two contacts. To understand your car you would be wise to invest in the factory service manual for it. Ebay is a good place to find copies at a good price. If you don't have a voltmeter that would be a very good investment also.
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Old 02-24-2015, 01:11 AM   #5
supremekizzle
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Quote:
Originally Posted by Cougar4 View Post
Your logic is correct. The two switches will work independently because they are in parallel with each other and the load is in series with the two switches. You could use a single ON-OFF-ON switch to do what you want to do with just the foot well lights. Tie ground to the center common contact and the light wires to the other two contacts. To understand your car you would be wise to invest in the factory service manual for it. Ebay is a good place to find copies at a good price. If you don't have a voltmeter that would be a very good investment also.
Thanks for your help. I do have an FSM, but the wiring sections are difficult to understand. I have decided to do it like this: white LEDs that come on with dome light and go off with dome light. I will tie into an accessory wire for the power and ground at dome. Secondly I will have red LEDs that come on with accessory and are to a normal ground with an on off toggle wire in in case I want them off. One thing I'm having trouble figuring out is how to incorporate my factory dimmer switch into the red circuit. Do you know which wire coming off of the center tree is for the dimmer and where in my circuit would I put this? I think that the purple wire going into my HU is dimmer? Maybe not. Ideally I'd like the red LEDs to come on with my headlights. Maybe tie into the light that illuminates the ashtray? However, I don't know how to incorporate the circuit with the dimmer switch. Would I blow the fuse that lights the ashtray light by tapping into it and drawing the power to run the LEDs? I really appreciate the help and could compensate you via Paypal if you could hook it up with a sketched out diagram of what I need to do. Thanks.

Edit: Maybe I can just tap into these for both illumination and dimming? Plus a toggle switch in between to turn off when needed.

Quote:
Subarus have two pins on the radio connector for illumination:
Pin 1 ("Illumination +") gets +12 volts when the parking or headlights are on; open-circuit otherwise.
Pin 7 ("Dimmer") changes voltage as you adjust the dimmer knob. It varies from about 10 volts (with knob at the dimmest setting) down to 0 volts (with knob at brightest setting). This pin is also called "Illumination - (minus)". Note that this is reverse from many other cars (where 0 volts = dimmest illumination).

Last edited by supremekizzle; 02-24-2015 at 01:53 AM.
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Old 02-24-2015, 12:16 PM   #6
Cougar4
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You're welcome for the help and I'm happy to give you hand with this. The factory wiring diagrams do take a little bit of time to figure out how they lay things out but it is pretty easy and there is a very logical flow to follow them. There is descriptive info at the beginning of the wire section that exlains some things about the service data.

The later model cars use a violet wire to provide power to the interior dash lights. The return side wire for those lights is usually orange I think and they tie to the lighting control module which is controlled by the dimmer control. The module changes resistance as directed by the control pot. The brighter the desired light is the less resistance to ground is provided through the module. The vehicles dimmer circuit is designed to control regular filament bulbs, not LEDs. You are going to need a specially designed controller for LEDs if you want to do that and you can get them from a number of sources.

I suggest you use a fuse tap to add the power provided for the white LEDs using the same fuse position that provides power to the dome light. That fuse may in the panel under the hood since it provides power at all times, not just when the ACC or ignition is on.

I can possibly help you with a drawing sometime after Thursday.
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Old 02-27-2015, 03:12 AM   #7
supremekizzle
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Quote:
Originally Posted by Cougar4 View Post
You're welcome for the help and I'm happy to give you hand with this. The factory wiring diagrams do take a little bit of time to figure out how they lay things out but it is pretty easy and there is a very logical flow to follow them. There is descriptive info at the beginning of the wire section that exlains some things about the service data.

The later model cars use a violet wire to provide power to the interior dash lights. The return side wire for those lights is usually orange I think and they tie to the lighting control module which is controlled by the dimmer control. The module changes resistance as directed by the control pot. The brighter the desired light is the less resistance to ground is provided through the module. The vehicles dimmer circuit is designed to control regular filament bulbs, not LEDs. You are going to need a specially designed controller for LEDs if you want to do that and you can get them from a number of sources.

I suggest you use a fuse tap to add the power provided for the white LEDs using the same fuse position that provides power to the dome light. That fuse may in the panel under the hood since it provides power at all times, not just when the ACC or ignition is on.

I can possibly help you with a drawing sometime after Thursday.
Further research points to dimming LEDs via pwm. However, how are the HVAC controls dimmed? Is there pwm built into that board and those LEDs? If so, possible to tap into that on/off frequency controlled for use in other LEDs? Thanks again for your continued suggestions.
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Old 02-27-2015, 08:07 AM   #8
Cougar4
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If the HVAC lights are LEDs then I would assume that something like a PWM controller is used for them and you might be able to parallel those lights with the new ones you want to install. The caution is that the new lights will require more current that the controller will have to provide to the added lights. If it can't handle the extra load then the controller will become damaged. I don't have any service data for SAAB vehicles so I can't really provide any real data on them.
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Old 02-27-2015, 02:08 PM   #9
supremekizzle
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Exactly the same as a 2005 WRX except for some body panels
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Old 02-27-2015, 06:10 PM   #10
Cougar4
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My guess is that the PWM controller will be able to handle the extra load. If you decide to try it I would go with the expectation you might have to replace it.
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Old 03-07-2015, 02:58 PM   #11
ThatGy
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The LEDs will dim with a standard resistive dimmer. I replaced the bulbs in my dash and the HVAC controls, and they dim quite well. As for pulling too much please by adding LEDs to your dome light circuit, a few really won't make a difference since they are such low power. The easiest thing would probably be to just replace the dome light and anything else inside the car with LEDs. This will lower the power significantly so that you can add more lights on that circuit without problems.
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Old 03-19-2015, 09:23 PM   #12
supremekizzle
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Quote:
Originally Posted by ThatGy View Post
The LEDs will dim with a standard resistive dimmer. I replaced the bulbs in my dash and the HVAC controls, and they dim quite well. As for pulling too much please by adding LEDs to your dome light circuit, a few really won't make a difference since they are such low power. The easiest thing would probably be to just replace the dome light and anything else inside the car with LEDs. This will lower the power significantly so that you can add more lights on that circuit without problems.
Just discovered this today when I put LEDs in the HVAC. They dim fine with the switch. I also put LEDs in my window switches. Quick question. Do you know what the leftmost (looking from the front) two pins on the HVAC are for? This is where I connected pos and neg for HVAC LEDs and would like to do the same for my windows switches and CIG lighter light now that I know LEDs can be dimmed on this circuit. Do you think it's the same as the two dimmer switches going to the radio? Thanks.
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