Gauge install, dash cluster light cable, Tach RPM cable help...

[King Tut]

You are correct.

[Acree]

Originally Posted by Sportsguy83

Thanks, any thoughts on the RPM cable? Preferably the one going to the Cluster?

Also, saw page 8 of the instructions you can change Dimmer max brightness 12V or ground, my uneducated guess is that that means it can be switched to be 0V full brightness.

Exactly. But as it sits, you'll only be able to dim it about 1/3 of the way. Tach signal I'll have to look in to.

-Acree

[xwd]

Originally Posted by Acree

The G/W wire runs at 4.1v no matter if the car is running or stopped.

The yellow wire goes from 0v at full brightness to ~3.8v at full dim. That's right, it's reversed. I'll have to look at this more closely tomorrow to figure out the simplest way to interface this dimming signal with your gauge.

-Acree

There isn't a good way to get a 0-12v with the newer Subarus which are PWM for most dimming. The older models used a 12v hot side (Ill+) and then a floating ground which was 0-12v (Ill-) which controlled the dimming. With the PWM models the Ill- (the B/W wire in your diagram) is a ground while the Ill+ is still +12v all the time. With the old models you could use a simple circuit to output a 0-12v signal for gauges to use.

Probably the easiest way to control dimming is use some kind of potentiometer unfortunately. Or build something to convert the PWM to an analog 0-12v signal...

Those wires you are looking at go to the gauge cluster directly I believe to control lights which are not LEDs? So they use the old method where they are 4.1v hot all the time on one side and reversed 0-3.8v based on the dimmer switch. Just my guess.

[Acree]

Originally Posted by dwx

There isn't a good way to get a 0-12v with the newer Subarus which are PWM for most dimming. The older models used a 12v hot side (Ill+) and then a floating ground which was 0-12v (Ill-) which controlled the dimming. With the PWM models the Ill- (the B/W wire in your diagram) is a ground while the Ill+ is still +12v all the time. With the old models you could use a simple circuit to output a 0-12v signal for gauges to use.

Probably the easiest way to control dimming is use some kind of potentiometer unfortunately. Or build something to convert the PWM to an analog 0-12v signal...

Those wires you are looking at go to the gauge cluster directly I believe to control lights which are not LEDs? So they use the old method where they are 4.1v hot all the time on one side and reversed 0-3.8v based on the dimmer switch. Just my guess.

That's a very good guess, but incorrect. The Ill- side is switched between ground and high with the PWM controller. The Ill+ is constant high. Ill- definitely never floats. They have pull-down resistors internal with the ECU.

And the gauge cluster is definitely LEDs... trust me on this. Check out my avatar. The picture below is the stock speedometer.

-Acree

[Acree]

As far as the RPM is concerned, the Failsafe gauge is looking for a square wave input. It calculates the RPM based on the programmed pulses per revolution in the AEM Failsafe Configuration software. Unfortunately there is no digital tach signal wire going to the combination meter (aka instrument cluster aka gauge cluster). The current RPM value is shared via CANBUS between the combination meter and the engine control module. The only wire with the necessary square wave signal is going directly from the Crankshaft Position Sensor to the ECM.

I do not know enough about the stock CPS to be able to tell you if this will work or not for the Failsafe Gauge. It depends on two things:
1) Find out what the resolution is on the stock crankshaft sensor wheel. This will depend on what type of sensor it is. It's more than likely a hall effect sensor. I would imagine that it has a pretty high resolution, something along the lines of 50-80 pulses per revolution.
2) Download the Failsafe Configuration software from AEM and plug in your failsafe gauge. Check the RPM Pulses per Revolution option and make sure you can select the same Pulses/Rev as the stock sensor.

If all of this checks out, I can figure out where and which wire you should splice into.

I do have to warn, in general as an EE, I would recommend against messing with any of the stock Crankshaft Position Sensor wiring. If you mess up that sensor, the wire, or the ECM, it's going to be pricey and labor intensive to fix it.

-Acree

[King Tut]

I am almost positive I got a PM from someone who hooked up the RPM wire of the failsafe to one of the wires I mentioned and that it worked. I checked my PMs, but I must have deleted it.

[xwd]

Originally Posted by Acree

That's a very good guess, but incorrect. The Ill- side is switched between ground and high with the PWM controller. The Ill+ is constant high. Ill- definitely never floats. They have pull-down resistors internal with the ECU.

And the gauge cluster is definitely LEDs... trust me on this. Check out my avatar. The picture below is the stock speedometer.

-Acree

Yeah I never said the PWM ground/signal floated, that was the old way Subaru controlled the analog dimming. I guess I didn't finish my sentence the PWM signal does switch between ground and high.

What do you suppose the roughly 4v signals are used for? Are those just regulated voltages for the cluster LEDs?

[Acree]

Originally Posted by dwx

Yeah I never said the PWM ground/signal floated, that was the old way Subaru controlled the analog dimming. I guess I didn't finish my sentence the PWM signal does switch between ground and high.

What do you suppose the roughly 4v signals are used for? Are those just regulated voltages for the cluster LEDs?

The voltage level is something that baffles me. In my experience, if a voltage is regulated anywhere between 3v and 5v, it's typically 3.3v. I've never seen 4, much less 4.1v.

What I am fairly certain of is the 4.1v is definitely not providing any power to the LEDs in the cluster. The illumination LEDs are internally regulated and grounded, either through the warning LED driver or the CPU.

King Tut,

I rechecked your post and I have to apologize. I definitely missed your details regarding the two wires. I do believe that the gray wire coming out of D48 would be suitable for the Tach signal. According to the wiring manual, it's coming out of the ECM labeled as "TACH."

-Acree

[Sportsguy83]

Originally Posted by King Tut

I am almost positive I got a PM from someone who hooked up the RPM wire of the failsafe to one of the wires I mentioned and that it worked. I checked my PMs, but I must have deleted it.

Originally Posted by Acree

King Tut,

I rechecked your post and I have to apologize. I definitely missed your details regarding the two wires. I do believe that the gray wire coming out of D48 would be suitable for the Tach signal. According to the wiring manual, it's coming out of the ECM labeled as "TACH."

-Acree

-Acree

I can live without dimming, since King Tut says it is livable. I did read King Tut's post about the cables that work, but I wanted one in the cluster . But also, I have no idea where are those pins... Any time you guys can take a pic or at least some directions and I'll figure it out from there.

I appreciate a LOT all of your help, including @dwx.

[King Tut]

Check pages 41 and 42 of the BRZwiring PDF for the locations of the two connectors that should have the tach signal. I don't know that you will find one behind the cluster. The gauge comes with plenty of wire to get to that side of the car though.

[Sportsguy83]

@Acree, I wonder if you got any more thoughts/ideas on the gauge dimming source. I still don't have my cluster, but just getting ready for it

[xwd]

Hey, as far as hooking up the illumination wire for my Greddy gauge, I used the Ill+ which is just a constant 12v switched on with the headlights. You can use the TAIL or PANEL fuses, they both go to 12v when the headlights are turned on. With that particular gauge, it doesn't use the 12v for powering the LED backlight, it just uses it to trigger the gauge to dim when it senses voltage on the line.

Getting something to dim with the dimmer (if that's your goal) is going to require some custom circuitry just like with the older Subaru models.

[chadstyle]

@Sportsguy83 I know I'm a little bit north of you but I'd be happy to help... If you have ever watched Street Customs then you would know I'm the "car audio guru"
@Acree has posted some very useful and technical information and he def knows what he's talking about. I'm sure I can get the dimmer to work properly in the aftermarket gauges...I've never let one beat me to date and in not about to start now.

[Sportsguy83]

Originally Posted by dwx

Hey, as far as hooking up the illumination wire for my Greddy gauge, I used the Ill+ which is just a constant 12v switched on with the headlights. You can use the TAIL or PANEL fuses, they both go to 12v when the headlights are turned on. With that particular gauge, it doesn't use the 12v for powering the LED backlight, it just uses it to trigger the gauge to dim when it senses voltage on the line.

Getting something to dim with the dimmer (if that's your goal) is going to require some custom circuitry just like with the older Subaru models.

I think I just need a 12V source. I don't care much about precise dimming, I usually just leave the dash lights full on all the time anyway. The Failsafe has an option to either have a 12V or 0V to trigger the gauge light up.

Where is the Ill+ located? I'm sorry for the stupid questions...