Installing the EATC Unit - Phase 1

First, I have to say I'm tremendously impressed with some of you! I've barely had this how-to started and I've gotten emails from people who have all the parts. One (Bob) has already done the bench test and verified his hardware and is ready to install!!! Bob also did some "proofreading" and found an error in the Ford documentation that I missed. You folks are on the ball!

So, with that in mind I'm starting the install document, though it will get better and have more pictures over time as I refine it. I feel like I need to get something there for the intrepid people who are ready and almost ready to install already.

The way it's going to work is that this page can be used to either do some preliminary work BEFORE the final install, or you can consider it the first page of the full installation. Phase 1 can be done without disabling your existing climate controls. However, once you start Phase 2, there is no going back -- at least, not easily.

A choice you may need to make

First of all, Between 1995 and at least 2003 (the last year I have any kind of tech data for), the Ranger used two different methods of engaging power for the blower motor. In addition, there are two different variants of the head unit, and the result is that you may have to make a choice about how to wire your blower power relay. I will cover ALL methods of wiring in this how-to.

1995 to 2000 Rangers -- no choice

From 1995 to 2000 the fan relay control works just like an Explorer! That is to say, we ground the relay to engage it. For 1995 to 2000 Rangers, no relay is required and we can put the EATC in with just a few wiring tricks and no additional relays.

So, for those of you with 1995 to 2000 trucks, and a 1998 or later EATC head unit (green display), your wiring is easy, and you have no choice to make.

However, 1995 to 1997 EATC head units (blue display) have NO main blower control output. This means that if you have a 1995 to 2000 truck and a 1995 to 1997 head unit, you will need an extra relay. You have no choice either. You need two relays total.

2001+ Rangers -- choose a method

If you have a 2001+ truck, and a 1995 to 1997 head unit as I have, you also have only one choice and no additional relay is required.

Finally, if you have a 2001+ truck and a 1998+ head unit, then you can choose to control the fan with or without a relay.

There are two ways to wire the fan power relay if you have a 1998 or later console and a 2001+ truck. You can control the relay with the EATC head unit, or you can just have it energize whenever the key is on.

The advantage of having the EATC control it is that you can turn off the fan even if the fan speed controller fails to "full on". Other than that there is no particular advantage.

The disadvantage of EATC control is that the Ranger and Explorer fan power relays work differently. The Explorer needs a ground to activate and that's how the EATC unit is wired. The Ranger needs +12 volts to activate the relay. So an ADDITIONAL relay is required to make it work this way.

On the other hand, the key-on fan power activation is simple, and requires no additional relay in the Ranger. I have mine wired this way; but the first two I did I put in a relay.

The disadvantage of the key-on method is if the fan speed controller fails, the fan will run at full speed every time you turn on the truck until you replace the speed controller. Not a big deal -- but it's your call.

What you need besides the EATC pieces

First, you need normal hand tools, a drill, etc. "End nippers" are nice for trimming the excess plastic tabs off the fan housing -- but you can always do something.

You will need a BUNCH of butt splices in all three sizes: yellow, blue and red. I never counted how many, but have at least a dozen of each of the red and blue, and a half dozen or so of the yellow ones on hand to be on the safe side. Also about a dozen "blue" insulated female spade connectors. Get the kind that have the insulation all the way down, not just on the crimp area. In the picture at the right are examples of all these things. The spade connectors are on the left side, butt splices in the middle, and tap splices on the right. For the spade lugs, get the type like on the top, not the ones with bare metal like the bottom. They will be used to connecto to the relays.

You will also need some of the "tap connectors" of the blue variety to tap the vehicle network and unswitched power from the radio.

You will need at least 1 automotive relay. Just an SPST 20 or 30 amp relay will be fine. If it has a mounting tab, remove it. We're going to stick it to the back of the controller with double sided adhesive and the tab will interfere when we mount the controller. This first relay is for the air conditioning compressor override. We will use the "rear fan off" control to let us switch off the A/C compressor when we want something like defrost without running the compressor. What we want is those small, plastic encased relays that are a cube about an inch on a side. Anything much bigger is hard to fit on the back of the head unit. Fortunately, this is the most common type. Here you can see two of them stuck to the back of the head unit. These particular ones have are "SPDT" types with an extra terminal called "87a" in the very center of the relay. You do NOT need this type, I just happened to have some around. Both are the same size/shape but the SPST type lacks the 87a terminal.

"SPST" and "SPDT" refer to the configuration of the relay -- "Single Pole Single Throw" and "Single Pole Double Throw". It's not a brand name or anything. I thought I'd throw that in for those of you who don't do a lot of this stuff.

The second relay will be required if you need to control the fan power relay with the EATC head unit. This relay will turn on and off when you turn the EATC unit on or off. Use the same kind of relay as the first one I mentioned. Radio Shack sells one, and they are available at most auto parts stores. Prices run from $5 to $15 generally.

In addition you need about 20 feet or so of 18 or 20 gauge twisted pair wire (shielded or unshielded doesn't matter). We'll use this wire to run to the sensors and the vehicle network. You don't want someting with real thick insulation on the individual wires in the pair though. With the sensors we will be combining 3 wires into one side of a splice and if they are too thick it makes it difficult. You will also need probably a foot or so of 10 gauge wire to ground the blower speed controller in the engine compartment.

A 3/4" "spade" boring bit (wood bit) to make the hole in the ductwork for the aspirator fitting.

Cable ties are a must to get the wiring under control and can be used to mount the outside temperature sensor as well.

Some silicone adhesive/sealant type stuff or gasketing of some sort to make sure the fan speed controller seals to the housing. If you're truly ambitious, you can cut your own gasket from sheets of gasket material.

Some prep work you can do

The following items can be done in advance of the full installation to save some time, or on the day of the installation, as you wish.

Aspirator connection

We need a place to tie in a tube for the aspirator that will draw air through our internal air sensor. If you slide your passenger seat back a bit, and get down in the footwell and look up under the dashboard, you'll see this view. This is towards the right side of the vehicle, looking up at the ductwork. In the Rangers I've seen, this area is generally the same. You won't see the green square I'm showing here as a highlight, but you will see that round "dimple" in the middle of it embossed on your ductwork. This is where you will drill a 3/4" hole using a spade wood boring bit. Take your time and don't heat up the plastic -- it doesn't take long to get through. If you are doing this in advance of the full install, just put a piece of duct tape over it to seal it until final installation.

If you recovered some stock tubing with the "elbow" it attached to, the tapered end of the elbow friction fits PERFECTLY into a 3/4" hole. You can use a little PVC pipe cement if you're not satisfied with the friction fit -- but it's pretty tight and none have fallen out yet. If you don't have the factory tubing, you should be able to cram some 3/4" I.D. bilge tubing in there and get it to stay, or improvise some kind of fitting. However, this location for the tap is important because it's on the suction side of the fan.

Below you can see two views contributed by the mysterious "Bob" (who doesn't want his full name used). I didn't get pictures of the aspirator connection and he took these of his. He's completed his installation now. Way to go, Bob! To the left you see the tubing run along the back behind the glove compartment hole. Note also that you can see the vacuum connection in the lower left, and his old actuator harness secured in the upper right. In the right hand picture you can see the salvaged factory "elbow" fitting used in the hole bored in the ductwork.

Fan housing modification to accept the speed controller

This is the fan housing which you can get to pretty easily once you remove the cruise control servo (which is one bolt). Here, the two screws which hold in the stock resistor in your truck have been removed and the resistor taken out of the way. Notice beneath the hole are two "tabs" that stick out. They are molded with right angles in them, and they are just below the hole to the left and right ends. These must be removed which can be done with cutters and then you can use a razor blade or whatever to shave them flat. These "rejection bosses" keep the wrong resistor from being mounted. Since we WANT to mount the wrong unit, it's necessary for us to get them out of the way.

Once you've removed them, you can test fit your speed controller. As you look at it in the picture, the left screw of the new speed controller will not line up with the old hole and you'll have to drill a suitable "pilot" hole in the housing. A 1/16 or 3/32 drill bit is usually good for this.

If you're not doing the whole install, then put the original hardware back in place when the prep work is completed.

If you are going to continue the install, you can mount the unit with the two original screws from your stock unit. Put a gasket on the unit or run a bead of sealant around the outer flange of the mount to seal the unit tight. We don't want water sucked in that will accelerate corrosion of the speed controller.

External (ambient) temperature sensor wiring

Run a pair of wires about 10 feet long from inside the cab to the front of the truck around the headlight area. The end in the cab should be run up into the center console where the EATC head unit will be installed. There should be about 6" of slack (at least) at that location so the wires will come out far enough to be spliced during the final install.

I bring the wires through a tiny slit cut in the periphery of the rubber grommet the parking brake cable comes through. You can get it through the firewall however you please; but whatever you do take care how you route it in the cab. You don't want it getting hung up in moving parts under the dash, or dangling down and catching your foot as you go for the brake. I run it DOWN from the hole and under the mat over to the center and then up to dash to prevent problems.

The other end should end up around the front headlight area. This end will be tied into the ambient sensor. Here we see the ambient sensor clipped into the body work below the headlight on the drivers side. This view is looking up from under the truck. There are some extra wires here because this guys truck had extra lighting, etc. If you can, get the little white nylon clip that holds the sensor in place on the donor vehicle. There are spots on the body sheet metal up front under the headlight where it can simply be clipped in place. This location is fairly well out of the engine heat, which is desirable. No matter where you choose to mount it, keep that in mind. There are several possible spots, but stay away from radiated engine heat and wash from the engine cooling fan.

If you don't have the original mounting piece, just tie wrap it or tape it to something. Keep the little tip clear and don't have it laying against anything so that it measures the temperature of the air and not the thing it's touching.

Go ahead and splice the sensors wires to the wire pair using red butt splices. The sensor has no "polarity" so it matters not which wire on the sensor you connect to which on the pair you ran. You can use a product called "liquid electrical tape" to seal the splices when you're done. It's not absolutely necessary, but it will make the connections last longer and prevent signal errors if you get road salt and water or sea water (both conductive) on the connections. You can do all this whether you're going to finish the install that day or not.

Interior (cab) sensor

Before you begin, extend the wiring harness of the interior sensor using red butt splices. You need about a foot or so. You don't need to seal these splices. Like the exterior sensor, this one has no polarity and it doesn't matter which wire is which. Usually these sensors come with VERY short harness stubs on them.

Remove the radio and the center bezel from the dash, exposing the area above your current heater controls. Just to the right of this area is the little oval vent on the soft part of the dashboard.

This sensor mounts to existing posts on the back of the dash right behind that vent. The hose can be removed to make it easier, but it's not necessary. If you can't get the sensor to stay on the posts, remove it and squeeze the spring clips on the sensor that go over the posts a little tighter. Not too tight though or it's hard to slide the sensor over the post. The sensor mounts with the hose connection facing DOWN.

If you like, you can route the hose up along the metal bracket above the glove compartment and over to the far right side of the truck and down to the hole you drilled in the ductwork. The picture to the right shows a typical installation. You will need either two pieces of the original white hose, or some of the 3/4" plastic bilge hose. You need about 4 feet or so of hose altogether, but buy 5 or 6 feet, at least. You can connect the end of the hose to the hole in the ductwork using a factory style angle fitting as discussed previously, or make something of your own.

Note that to run the tubing you will have to drop the glove compartment by squeezing the ends in and pulling it out and down. In the picture above, Bob removed the glove compartment completely, but it's not required. Depending on how you route it, you may need to remove the airbag also. There are two bolts over the glove compartment area that hold it in, then one connector to pull off.

IMPORTANT SAFETY CONSIDERATION: Airbags are explosive devices. There is a danger in handling and connecting them. Proceed at your own risk. When disconnecting and connecting it, hold it so it's at a right angle to your face. Then if it blows, it will blow to the side and cause you less injury. I do not know of any ever blowing -- but it's better to be safe.

Sunload sensor

If you haven't already done so to run the aspirator tube, drop the glove compartment door and remove the airbag, paying attention to the warning above.

Like the interior sensor, you need to extend the wires. Make these extensions about 2 feet long and splice them with red butt splices.

This sensor also has little spring clips that attach it to existing posts on the underside of the dashboard -- more specifically the black plastic piece that surrounds the defroster vents at the base of the windshield. Here you can see it clipped in place. You can remove the CSM (central security module), the white box dominating the left hand side of the picture. You don't have one if you don't have power locks. It comes out with two screws so if it's in the way it's easy to move. Once the sensor is snapped in place, route the harness down and into the central dash area.

Wiring the relays

As previously discussed, you will be sticking either one or two relays to the back of the EATC head unit with double sided adhesive as shown here. I have the relays aligned differently relative to the way the diagrams are drawn below, but for no particular reason. It doesn't matter which way you have them on there as long as you get the numbering correct! Don't worry, it's marked on the relay. I didn't show it as different in my diagram, but terminal 30 is the terminal that is rotated relative to the others in the middle row, the left hand terminal on each relay, as shown here. If you are good with wiring, then you know you can rearrange even the terminals to some extent and you're welcome to do so. If you're not savvy, it's probably best to just set it up to match the diagrams below.

One note: all the diagrams contain a reference to "switched 12 volts" and what that means is that the wire on that terminal will be connected to either of two wires in your existing vehicle harness. Those wires are GY/YE and BK/LG. You will also be using one of those wires from your truck to supply switched (that is, hot when the key is on) power to the EATC head.

Here's how they will be wired.

This diagram applies ONLY to 2001+ Rangers with '98+ EATC head units. In this phase, you will not be connecting the purple or red/orange wires from the vehicle harness. Crimp female spade lugs on each of the PU, and RD/OR wires (from the "Miscellaneous" group); and YE/BK wires (from the "Fan relay and speed control" group) coming from the EATC harness and slide them onto the correct terminal on each relay. Check first to make sure the wires can REACH the terminals of the relays and extend them if you have to. Then cut 2 pieces of wire 2" long, and one piece a foot long. Strip the ends of all three pieces about 1/4" to 3/8". Place one end of each of the 2" wires in a single spade lug and crimp them in place. Crimp a spade lug onto the other end of one of the 2" wires. Now take the remaining 2" wire end, and one end of the foot long wire and crimp them into a single spade lug. Now put this assembly on the relay terminals as shown so that 86 is connected on the left relay, and 85 and 30 on the right one. The foot long wire should dangle free.

Here is what you will be doing if your vehicle requires only one relay (the one for the A/C compressor override). If you require only one relay, that means we are using another method to control the fan power relay. This diagram applies to any truck from 1995 on with a 1998+ EATC head. With 2001+ trucks it may be you've chosen not to use a relay. In older trucks, we can control the truck directly without a relay. In both these cases, you will be using this diagram, and we'll cover the fan control final wiring in the second part of the how-to. Simply put female spade connectors on the PU wire and the RD/OR wire (from the "Miscellaneous" group) and place them on the correct terminals on the relay. Make a 1 foot 18 to 22 gauge jumper and put a female spade connector on one end and attach it. The other end remains unterminated until we do the final install.

And finally, here is what you do if you are using the older style pre-1998 EATC with a '95-'00 truck. Like the other diagrams, you won't be terminating the wires which go to the truck. Cut 1 piece of black 18 to 22 ga wire about 2" long, and another about a foot long. Strip all of them about 1/4" to 3/8". Put one end of each of the wires into a female spade connector and crimp them tightly. Now crimp another on the end of the 2" wire. Now slide the spade lugs over the appropriate ground terminals (86 and 87) of the fan power relay (the one on the right). Make an identical wire and lug assemble from a different color wire and put it on terminal 86 of the compressor relay (left relay here), and the fan control relay (right). Put lugs on the PU wire coming from the EATC, and the RD/OR wire (from the "Miscellaneous" wire group) and put them on the correct terminals on the fan control relay.

Tapping the vehicle OBD-II network

In this view, we are crouched down, looking up at the area under the dash directly below the steering column. At the very top center, is the OBD-II connector used for scan tools and the wires we want attach to it. We need to tap the TN/OR and PK/LB wires in this bundle and you can see here that I've done that using red tap splices. You can use blue also (I was out of blue). I'm not sure which is SUPPOSED to be used, but they both work. Besides the position you have to work in, you have to separate these two twisted-together wires enough to tap them both and it's a pain -- literally -- to do. What you need to do is make a connection using a 2 foot pair of wires to these, keeping track of which wire is which. The pair wire like we used for the sensors is good for this. If your wire is 20 or 22 gauge use red taps, but for 18 you can really use either.

One thing: when you are done, route the wire up into the center dash area near the existing heater controls and MAKE SURE THE ENDS ARE TAPED OFF AND CANNOT SHORT TOGETHER OR TO OTHER THINGS. The reason is that this network can be important to vehicle operation and you don't want it shorted out.

Also, write down somewhere which wire goes to which color on the wires under the steering wheel. It's important to get them hooked up correctly when you do the final install.

Last, if you have a 1995 EATC unit it doesn't have the vehicle network connection so don't bother!

This concludes Phase 1 of the installation.