FAQ: Installing the AUTO I/C Spray the right way

[mrsaturn7085]

First things first - you need to have a standalone with 1 low-side input and 1 pulsed ground output available. Wiring this to work with a JDM (16-bit) ECU on a 32-bit chassis loom is well beyond the scope of this post.

I'm going to keep this short and sweet, and hope that it will just become a sticky. This is intended for the GD chassis and you will need to reference the FSM. The following image explains it all:



Red highlighted lines are short-length added wires.
Yellow highlighted lines are dash-spanning added wires.
Dots attached to red or yellow highlighted wires are splices.

You only need to interrupt a single wire in the entire factory harness to make this work. You will need to make a few splices elsewhere, but everything will continue to work as OEM if you follow my wiring plan. This is useful to note if you ever choose to replace the standalone ECU with a factory one.

This wiring replicates the OEM wiring in that it will automatically disable the I/C AUTO spray when the water tank is empty. If the AUTO switch is depressed with an empty tank, the orange 'active' light will turn off and the I/C water low warning light on the dash will illuminate.

Part Notes:

A - 1.5A diode (~20VDC or better rating); the OEM part can be sourced from a junkyard rear wiring harness near the OEM I/C spray tank in the trunk. You don't *need* the OEM part, but it has a handy in-line holder. (Located near ECU)

B - Nissan relay; the easiest way to source this is to buy a used DRL relay pack from just about ANY Subaru with DRLs. The following image is one of about 100+ available cheap on eBay. You want the black relay and be sure to buy it with the chopped connector pigtail! (Located on I/C spray timer bracket)



C - Subaru relay (82501AE03A aka 82501FC100) w/Hella HL87125 micro relay holder; can't get much easier than this. (Located near I/C spray timer bracket - just zip-tie it in there somewhere)

D - Auto I/C switch (83001FE030) and connector; the connector is the tough part if you don't find the switch with a pigtail. The generic (non-keyed) connector is a Yazaki 7123-1360 or Sumitomo 6244-5061. Searching for a "Sumitomo 6 Position 090 MT Connector" will likely get you what you need. (Located next to the OEM I/C Spray switch)

I recommend the following splices (they are expensive, but MIL/Aero quality); you will need blue (medium) and yellow (large) sizes, but it doesn't hurt to have some red (small), as well:

650-D-436-38 (D-436-38)
650-D-436-37 (D-436-37)
650-D-436-36 (D-436-36)

You need the proper crimp tool and a heat gun capable of 700 deg F to install these.

Now as far as the ECU signals go, the wire with the inline diode is the input for the AUTO mode. When the AUTO switch is depressed, this wire sends a switched ground signal to the ECU. The ECU must be set to read this pin as an active-low input (and therefore must have an internal pull-up resistor, usually to 5 or 12 VDC).

The other ECU pin is the output pin. When programmed conditions are met, this wire sends a 0.5 sec ground signal which is extended to 2 seconds through the OEM timer. The delay between 0.5 sec pulses should be programmed to be short enough to keep the IAT cool without running out of water too soon. With a 12 liter tank, I have my current 'OFF' time delay set to 5 seconds, but might adjust it as needed.

The JDM ECU has an elaborate algorithm that only allows the AUTO spray to happen when a handful of conditions are met (minimum RPM, minimum boost, minimum IAT, minimum TPS, etc.). MOST aftermarket ECUs will NOT allow this many variables, so I suggest one of two options:

ON above 90% throttle, OFF below 80% throttle

-or-

ON above 40 deg C IAT, OFF below 38 deg C IAT

The hysteresis will prevent hitting points where your AUTO I/C spray will be clicking on and off frequently.

Lastly, for the GR and later folks, here is the OEM wiring for the Spec C; it only differs in a few small ways from the GD wiring, so you should be able to reverse-engineer your own solution without much trouble: