Where can I tap into a “dimmed” instrument cluster power?
 

Hi guys,

Probably a simple question for those who’ve done a lot of wiring.

I want to add a couple of switches in my 86 on the dash for a project I’m planning.

I would like to use illuminated buttons/switches.

Button example: https://www.amazon.com/dp/B01G00GHQ4..._I0Z1BbGGA944Q

I would like to wire the illumination on the buttons/switches separate from the on/off so that they are illuminated regardless of wether the switch is on or off. Basically so that I can find the switch/button in the dark.

Ideally I would like to power the leds in the switches with the dimming power that comes off of the instrument cluster/gauges and factory switches so that the switches illuminate when the headlights are on and dim with the factory instrument dimmer knob. Then I’ll use red led switches for a nice oem look.

My question is, is there a pair of wires that’s easy to tap into for this dimming power signal behind the dash?

Maybe off the back of the radio harness, clock, or the dimmer knob itself?

I will just be powering 3 small leds so I don’t think I need to add a fancy circuit of a fuse or anything, this is just to illuminate the switches themselves.

I did notice that the stereo has a “illumination/dimmer” wire in the 10 pin speaker plug, but I’m unclear if this provides the “dimmed” signal or just provides 12v to tell the radio to do its own dimming.

Can I use common ground with instrument cluster power? Or should I connect my negative back to a ground on the dimmer/instrument cluster circuit?

I’ve read repeatedly that Subaru uses a weird circuit for dimming so I want to make sure I do this right.

Thanks!

The factory "ILL" wire is as you said, a signal wire. Dimming is done with the negative wire, either by the knob or ECU depending on the light you're talking about. The radio dims internally.

It may be possible to use the ground that goes through the dimming knob, but there is an inherent risk to the entire system if you do that. Also, seeing as you're using aftermarket LEDs, you'll want to test it as well to make sure it works properly. Many LEDs need a PWM to dim properly.

If it were me, I'd pull out the dimmer switch, test out the wires, tap into the necessary ground and run an LED off it (with a diode in place to prevent any unwanted frying of stuff). See where that gets you first.

Thanks for the reply.

Subaru’s dimmer system really is an odd one.

Knowing that the factory footwell lighting kit dims with the instruments I looked it up.

It appears that it ties into the hazard lights button and clock circuit.

Looking at pictures of it, the wires don’t make any sense. There appears to be 3 wires going to each led harness.

Too bad it costs so much or I would buy it for the harness.

Image and install instructions below:
https://rover.ebay.com/rover/0/0/0?m...2F192537581660

http://www.ft86speedfactory.com/inst...H701SCA100.pdf

add an arduino to the system, use the ILL wire as a signal and use the PWM from arduino to dim the lights. Also if you do any wire tapping, add in diodes to decrease the risk of back voltage.

Not strange at all. They're tapping into that same ILL wire that everything else uses. Remember, the hazard button lights up at night and the clock dims slightly, so they use that same circuit that everything else does as the signal or source. They just chose to make a harness for that connector to get at it, that's all.

The kit you linked only has 2 wires to each LED, as it should be. Yellow and black. It's doing exactly what I suggested you test, using the ILL circuit as a trigger, and the ground circuit that goes into the dial as the dim setting.

The only thing I don't personally like is that it's using the ILL circuit as the 12v power source, but LEDs have such low draw that it isn't really an issue and it's OEM, so it's engineered to work as is. I like to isolate DIYs from that circuit to their own fuse so if something I do shorts out, it only blows the fuse for the DIY stuff and not anything factory.

Out of curiosity, how many switches are you adding, and where are you placing them?

I want to add 3 momentary button switches. I haven't decided on exact placement yet, but somewhere near the center console. Maybe on a trim piece this is cheap to replace if I ever want/need to return it to stock. like the shifter boot bezel or those silver pieces on the back of the knee pads. Also toying with the radio bezel as a location.

I'm trying to add physical next/back and mode buttons for the stock radio because I hate using the touch screen at speed on bumpy roads.

The buttons don't have to light up, but I thought it would look cool, be oem looking, and make the buttons easy to find in the dark.

The photo on ebay looked like 3.. could be common ground or a bad photo.

I was thinking last night, that I always keep my instrument lights at the same brightness (super dim, almost off) so I could take the easy route and just use some resistors in line to dim the led's to a level I like and just accept them always being one brightness... might be easier.

This seems like a lot of work just to get a physical skip button..

why don't you get one of these Bluetooth kinda things? Stick it wherever you want
https://i.ebayimg.com/images/g/vX0AA...j7/s-l1600.jpg

otherwise have to looked into different HU's with physical buttons?

it is, but seemed like a fun project. I haven't found a bluetooth remote with good reviews, and this would control the suriusmx and stuff as well.

Swapping head units is a much more expensive prospect imo.

Have you verified the radio can even do this? It's usually not just as simple as connecting wires, it requires a module or interface to interpret the signals from the buttons into signals the radio expects, inputting onto probably unused pins on the head unit. Typically this is done the other way, retaining stock buttons to aftermarket radios, and I can tell you those don't just send straight 12v signals, they send pulses corresponding to the different type of button pressed.

Yep. It’s been done.

The stock radio interprets different resistance values on some of the un-used pins (21, 22, & 23) as steering wheel controls. Doesn’t even require power.

Normally this is done with 4 rocker switches but I was just going to leave out the phone controls and volume.

http://www.ft86club.com/forums/showthread.php?t=39244
http://www.ft86club.com/forums/showthread.php?t=44827

Good read, that makes sense!

In that case, just follow what I posted above, make sure you have the proper pin momentary switches (the link you put up earlier looks good), and you'll be good to go. Just keep in mind you'll need to use completely separate grounds for the radio signal common pin and the LED if you integrate it with the dimmer switch, as that switch will change your resistance and would mess with the radio signals if you combined them.

Yep. My thought was 2 pins to do power and ground for the leds. 2 normally open pins do the switching on of the different resistors.

While you might leach 12v off the switch positive to light the led for a powered circuit, you wouldn’t want that in this case.

Seems most illuminated buttons have this ability.

Ie this one:
Quentacy Momentary Push Button Switch 1NO1NC Waterproof Silver Stainless Steel Shell 12V LED Ring Illuminated Switch Wire Socket Plug Suitable 19mm 3/4 Mounting Hole (Red) https://www.amazon.com/dp/B075Q9QSX4..._9yq2Bb0Q442YS

I would just ignore the NC lead I believe.

So I think, find the ground in the dash dimmer switch, and use that as my led negative. Use The radio’s illumination wire as my led positive. That should in theory make the leds light up and hopefully dim with the instruments. Then wire up my separate wires with the required resistors to make the buttons send the commands to the radio pins.

I’ll test it all first but I think this just might work.