SaabCentral Forums banner
1 - 9 of 9 Posts

·
Registered
Joined
·
898 Posts
Discussion Starter · #1 ·
Hey all,

I have an extra dimmer rheostat that I want to use for some extra LED lighting installing that I am doing. There are many pins/wires on the back, and I was wondering if any of you knew how i might wire this, and what pins to use. I assume it's as simple as having the rheostat inline with the power source, with a 12v going in and the current coming out would just be resisted according to the setting? I don't know how they work.

Anyway, some help on this would be great. Thanks!
 

·
Registered
Joined
·
12,793 Posts
Hi Nils,

Hopefully this will help.
Pin 1 (Black Wire) - Ground
Pin 7 (Green/White Wire) +12V (ignition on via Fuse 29)
Pin 2 (Purple/White Wire) - Output Voltage to SID and dash cluster
Pin 3 (Gray/White Wire) - Output Voltage to various illuminated switches
Pin 5 (Gray/Red Wire) - Output Voltage to headlight/fog light switches and light around ignition
Pin 9 (Gray/White Wire) - Output Voltage to MCC/ACC

So basically connect pin 1 to ground, pin 7 to +12V and then use any of the other pins for output voltage.

See also: https://docs.google.com/open?id=0B0NHQc9CqcaXYzRpdk9zNE1qTVU
 

·
Registered
Joined
·
898 Posts
Discussion Starter · #5 ·
Ah, perfect, thank you very much. I had tried this before and it flat out didn't work, perhaps it was because I didn't have a ground wire for the switch. Thanks Jake
 

·
Registered
Joined
·
12,793 Posts
No problem, if like Kei says it is controlled my a micro controller, then you would need both +12V and Ground connected to power the micro controller and then you would connect any of the outputs to the +ve leg of the LED and the -ve leg to any ground point.

You may also want to look into using variable resistors with the LEDs, since the rheostat just controls the voltage (think of it like an adjustable voltage regulator) you will still want to regulate the current (via the resistor) and ohms of the correct resistor is dependent on source voltage (which in this case varies).
 

·
Registered
Joined
·
898 Posts
Discussion Starter · #7 ·
Okay, that makes sense why it wasn't working before then. Why should I also resist the current? Is that because LED's won't respond very dynamically to voltage change?
 

·
Registered
Joined
·
12,793 Posts
LEDs draw a small amount of current, hence one of the reasons why they are preferred over incandescent bulbs, to provide the LED with its correct safe amperage you use a resistor.
Most LED arrays come per-assembled with the correct resistors for the voltage they are meant to be used at, but since in the case of using the rheostat (adjustable voltage regulator) the voltage will vary then the resistance should vary too.
You can use the resistance for the upper end of the voltage the LEDs will see and everything will be safe, they just wont perform to their optimum when the voltage drops.
Anyway not sure if you are building your own arrays or not, but if so just something to consider.
 

·
Registered
Joined
·
898 Posts
Discussion Starter · #9 ·
Okay, well thanks for that info. I am using prebuilt LED modules. If it doesn't work with the saab rheostat I will just wire them without a dimmer, its not a big deal. Thanks!
 
1 - 9 of 9 Posts
Top