Tekonsha P3 Brake Control,
Charge Circuit and Aux Fuse Panel
Update 09/22/08: A while back, RAV4World member Jeremy Lauer sent me a very nice wiring schematic he drew for the Tekonsha controller. Sorry it took me a while to get it posted - I sort of forgot about it ;(
Docs\RAV4 brake controller wiring schematic - Jeremiah Lauer.pdf
Update 03/26/08: It appears that many owners are receiving parts with no instructions, and it is sometimes difficult to find the instructions online, so here is a Toyota installation document in pdf format:
Docs\RAV4_Trailer_Wire_Harness.pdf
CAUTION: Disconnect the battery ground cable until all electrical work has been completed!
There has been a lot of pissing and moaning online at RAV4World about how Toyota delivers your "Tow Prep Equipped" RAV4 V6 with upgraded cooling and charging systems, but you still have to spend a small fortune to install the receiver and a complicated wiring harness to get the trailer lights to function. The Mother Ship requires (on page 344 of the Owner's Manual) that the trailer have functioning brakes if its weight exceeds 600 pounds. So now we have to figure out how to install the necessary brake controller, wiring and an RV-standard 7 pin trailer connector. Since we are ripping out much of the interior and dash, we might as well install a Trailer Battery Charge circuit, in case the trailer has either a "house" or an emergency break-away battery. Oh yeah, where do we pick up power for all that? Time for an Aux Fuse Panel!
I decided to install the OEM trailer wiring harness to get the trailer lights working. It's plug and play, but requires removing much of the left side of the interior to run the harness up front to the relay box over the driver's left knee. That installation went relatively smoothly (other than the hair-pulling hunt for the A5 connector under the dash) - there is a great illustrated report here that you should read first if you plan on installing this harness: Tow Hitch Wiring Guide. If you want more information or need to ask a question, here is the thread on that subject: RAV4World - Tow Hitch Wiring Guide
For the brake and charge wires, we need heavy gauge primary wire to eliminate unnecessary voltage drop on the long run back to the trailer connector. I chose 12 AWG blue for the brake and 12 AWG red for the charge wire. Important: regular blue crimp terminals and splices will "just barely" fit on this size wire. For the main feed cable to the new fuse box, I chose 10 AWG white, and used yellow self-soldering insulated ring terminals.
Dexter 7 inch brake magnet "full load" current is about 5.0 amps per axle (a pair of brakes), but the big 10x2 inch brakes on my trailer's 3500 pound axle draw a total of 6 amps, so that is probably the most you would normally see on any trailer the RAV4 could safely pull. A discharged house battery on a pop-up trailer will draw some serious current at first, so we need good sized conductors with circuit breaker protection against shorts. Dexter recommends a minimum wire size of 14 AWG to be safe. Link: Dexter Axle - Trailer Axles and Running Gear Components - FAQ'S
Most of the parts needed - this particular 7 Pin "RV standard" connector also
has a built in 4 pin connector on the left side. It has a pigtail with 4 pin
connector which will tie into the factory lighting harness. The other circuits
have short pigtails with pre-installed yellow butt splices. The steel mounting
bracket came in the kit. The split loom is 1/4 inch ID, just large enough to
hold both 12AWG wires. Going larger would just make it harder to route the
wires. Not shown is the white 10 AWG main supply wire or MaxiFuse fuse block -
I'll show more of them later. I also bought a couple of assortment packs of
steel and rubber "Adel" clamps to secure the cabling if needed. All
these parts came from NAPA Auto Parts, with the exception of the Maxi Fuse stuff,
which is from a marine supply on eBay.
UPDATE 06/09/08: The 7 pin socket is a Hopkins (AKA Hoppy) 47185 "Multi-Tow 7:4" - Amazon.com: Hopkins Plug-In Simple 47185 Multitow 7:4 Adapter: Automotive.
Here is a great FAQ on trailer wiring. How to Wire Your Car or Truck for Trailer Lights. It discusses uses for the "extra" pin in the 7 pin round RV connector. The only improvement I can suggest is to NOT rely on trailer frame ground for the trailer lights! It is much more satisfactory in the long term to add additional white ground wires from each light to a common terminal strip mounted near the coupler, and connect the white front harness ground wire to that point. This mod may save you countless hours of troubleshooting and swearing on some dark back road, when your lights quit because of faulty frame grounds.
I also strongly recommend that you buy a US$12 LED tester that you can use to quickly verify that the vehicle wiring is correct. This can save hours of probing (and swearing) with a meter:
Plug in LED tester to check vehicle wiring integrity.
This plastic Buss fuse panel is compact and inexpensive (about US$10). It
accepts regular (large) bladed ATC fuses or similar plug-in circuit breakers.
I chose a couple of 20 amp self-resetting C/Bs which will open to protect the
wiring if there is a short circuit, but will automatically close again after a
few seconds. The legs are too long and have to be trimmed at the first notch to
let the housing go down flush against the panel.
The Hoppy 7 pin connector, with the spring loaded weather cover held open. The 4
pin connector is to the left. I chose a plastic connector because I have had
corrosion problems with the plated steel connectors in the past - the inside
rusts and shorts out the wires, causing severe electrical hassles! MSRP
with steel mounting bracket is US$30. It was on sale for $20.
CAUTION: Disconnect the battery ground cable until all electrical work has been completed!
The left cargo floor with the side trim panel removed. Discard the large blank
rubber grommet near the top - the factory lighting harness and the two extra
wires go through the hole.
A poor pic of the factory wire harness with the two extra 12AWG wires pushed
through the center hole.
The split loom is in place and the connection to the grommet is re-sealed with
electrical tape. Another few turns of the tape secures the extra wires to the
white plastic cable clip.
The factory harness and extra wires in place through the hole in the side
structure. The square black plate is the newly installed left inner backing
plate for the OEM receiver. The gray foam tape is part of the light harness kit.
The extra wires follow the Toyota light harness along the door sills and up to
the dashboard.
I mounted the trailer connector under the cargo compartment at the far left, in
the cavity between the side of the under-floor bin and the wheel well. It's out
of the way but easy to access from the back of the trucklet when plugging in the
trailer. This can be a REALLY wet environment - it's important to angle the
connector down to let it drain, and to make sure the connections are weather
tight. I used silicone sealant on the butt splices before covering with half
inch split loom, and also a dab of sealer on each mounting screw to keep water
out of the cargo bin. I also used silicone dielectric grease on the 4-pin
connection on the right (rear) to keep out water and reduce the chance of
corrosion.
The arrows point to the two 8-32 screws for the the 7 Pin connector bracket. I
cut away the sound insulation so the upper screw head would pull tight against
the sheet metal. The Toyota 4 pin connector, which is at the end of the OEM
trailer lighting harness, is screwed to the panel to the rear (left) and
out of sight in this pic. The screws are covered by the black carpet liner of
the cargo bin.
This pic shows how the trailer's harness plugs into the 7 pin socket. The cable
runs along the bottom of the left main tube of the receiver, and is held up by
the OEM mounting plate for the Toyota 4-pin connector (which got relocated in
the previous step.)
Now it was time to move up front - the 12 AWG wires are routed and secured
alongside the Toyota trailer harness. This area (forward of the main glove box)
was the best spot I found for a fuse panel - it's easy to access with no tools,
protected from the elements, and most important, there's a real easy way to get
a fat 10 AWG wire through the firewall a few inches away! There are two Black
Boxes attached to the curved steel bracket. Remove the two 6 mm bolts and let
the boxes hang. Remove the upper bracket nut and lower bolt, unclip the plastic
wire harness clip, and pull out the bracket.
I felt that the fuse panel needed some support, so I cut a short length of 1/8th
inch aluminum plate and drilled two mounting holes as shown in the plate and the
bracket, so the top of the fuse panel was parallel with the bend line, near the
top of the pic.
The panel installed with two 8-32 screws and nuts. I used lock washers AND blue
Loctite, since I really didn't want this thing to come loose and short out!
The modified curved bracket and the Black Boxes bolted back in place.
Up and to the right is a large rubber grommet with a wire harness and clear
windshield washer hose coming through. Unfortunately it's a double firewall and
a double grommet, and because I couldn't really see where the drill bit was
going to end up I decided to use a length of aluminum tubing as a "fid" to feed
the wire through the double grommet. I drilled a small hole at about the 8
o'clock position in the rear-most grommet only. I lubed the tubing with liquid
dish soap, placed the wire part way inside and pushed the tubing into the hole.
The front side of the front grommet is easily seen from the engine bay, just
behind the strut tower. By pushing hard on the tube I could see the "bulge" and
reposition it as needed to get it to emerge in the correct spot, near the
center, but not jammed up against the other wires. Once I was satisfied with the
position I slit the grommet with an Exacto knife and pushed the tube the rest of
the way through, as shown here. EDIT 06/09/08: Then
I pulled the tube and about 6 feet of wire through the grommet, and discarded
the tube.
The nearly finished fuse panel, with the 10AWG wire connected to the bottom lug
and covered with a red plastic boot to prevent unpleasant surprises for the
Toyota mechanic. The red Charge wire and blue Brake wire are connected using
crimp-type insulated 1/4 inch wide spade terminals. The two breakers' flat
terminals are trimmed with a set of side cutters and plugged into two of the
positions.
EDIT 06/09/08: The boot is a marine alternator terminal boot, for 10 through 6 AWG wire.
NOTE: I used the same blue wire to feed the brake controller, and also to carry the modulated current back to the rear of the trucklet. I just left a 12 inch loop of extra wire under the steering column so I could cut and splice it into the controller harness later - I used an ohm meter to verify which blue cut end came from the breaker panel. Notice that there are 4 extra circuits on the panel available for powering driving lights or other stuff.
This angle shows the new harness looping up and over to the firewall grommet.
The arrow points to the spot where the white wire goes through the rubber into
the engine compartment.
I discovered that the C/B covers rattled, so I put a strip of electrical tape
across them to keep them quiet and also labeled the panel so a stranger would
have an idea what it is. 50 amps is the main fuse rating, not the safe working
load. I also covered the un-used slots to keep them clean. The 4 exposed flat
terminals are safe - without fuses or C/Bs installed they are not Hot.
The white cable, protected by split loom, runs across the top of the firewall
along an existing wire bundle. I took this pic before cutting off the wire ties
so it would be more visible.
Route the wire across the top of the brake reservoir and secure it to the empty
threaded stud using a metal and rubber clamp, and a 6 mm self-locking nut.
Here's the Blue Sea Maxi Fuse Block mounted on a
fabricated steel bracket. The 50 amp fuse is available from NAPA or other auto
parts stores for about US$3.00 - I bought a spare for the glove box. The fuse
block is a marine part, and can be found at West Marine stores and also online.
Mine came from eBay for about US$20 plus shipping.
MAXI Fuse
Block - Blue Sea Systems
The fuse is installed with Dow Corning DC4 silicone dielectric grease, and the
24 inch short battery cable is attached to one terminal. The screws clamp down
hard on the fuse tabs, making a tight connection. Here's one source for DC4:
Dow Corning DC4 Electrical Insulating
Compound (5.3 oz. tube) - SkyGeek.com
I used these new Belden self-soldering terminals - they are quick and easy, but
I'm not sure I would rely on them for a high current load like a starter. Two
pieces of heat shrink tubing is pre-loaded on to the cable, then the terminal
sleeve is shrunk using a propane torch with diffuser. Extra heat is added to the
ring to melt the solder. (Caution: If you melt the
solder before shrinking the sleeve, the solder can run out the bottom.) Slide
the pieces of heat shrink over the terminal and shrink them one at a time.
The finished cable, with lots of "stress relief" to
protect the joint. Next slide the split loom into place and tape it securely.
I installed a small strip of wide black electrical tape to act as a splash/ dust
guard - the DC4 takes care of moisture issues. The bracket fits nicely under the
ECU front bracket. The left fuse box cover is removed here for clarity.
CAUTION!: make sure when building the new bracket,
that the front tab of the left fuse box cover clears it, or you may not be able
to install or remove the cover.
Modify the battery positive cover as shown here, to make room for the extra
cable to exit the rear corner. Don't cut away the small internal clip that
latches over the terminal!
Install the battery cable onto the positive post, and
install the modified cover. Clip and cut away the Toyota wire ties at the two
battery cable supports, thread in new nylon ties, and secure both cables
tightly.
The finished cable and Maxi Fuse installation.
The Tekonsha P3 controller mounted on top of the center switch panel. It angles
down steeply but you can still easily reach the manual control lever underneath,
using your index finger. The slot on top is for the other Quick Release bracket,
which I chose not to use. 90% of the control, including most of the bracket, is
out of sight when installed in the center console.
It's a very simple mount using the "classic" fixed mount bracket and a couple of
8-32 screws. The unit should be aligned parallel with the centerline of the
vehicle - which means you should use the forward (inside) edge of the panel as a
guide, not the exposed curved edge.
This shot shows the required angle - tighten the side screws pretty tight, so
that the box won't move, but so that you can still force it a little as needed.
The pink clip in the foreground is one of the securing clips that hold the
switch panel in place - just snap the panel back into the holes. Removal is
really easy with the P3 installed - just grab and pull. I left a loop of extra
cable inside the console opening so it would be easy to plug the connector into
the P3.
Section of the factory wiring diagram showing the brake light switch. The wire
marked "L" is the blue wire that we are after - it supplies the brake signal
that triggers the P3.
EDIT 06/09/08: the wire is in the lower left corner of the diagram, at the stop lamp switch.
Here's the brake light switch harness with the split loom pulled back, showing
the red trigger wire spliced and soldered (using rosin core electrical solder!)
to the Toyota blue wire. Access is super easy with the steel cross piece removed
(2 bolts).
The finished brake control connections with the cross brace reinstalled. The fat
black wire on the right supplies 12 volts direct from the circuit breaker into the P3. The fat blue wire on the right is the
trailer brake supply wire coming
back out of the P3 and then back to the trailer. The white wire is a ground that attaches at the brake pedal pivot
bolt using a 3/8 inch ring terminal. The wire had a prominent warning saying
that the unit might not work right if the ground wasn't attached direct to the
battery, but that is Lawyer Speak - as long as the steel bracket is attached
solidly to the structure it will be fine.
Reconnect the battery negative cable, with fingers crossed!
The finished P3 installation, ignition turned off.
The display lights up whenever any activity is noted by the brake control - such
as stepping on the brake or turning the key. It goes out after a few minutes if
nothing else happens to prevent battery drain.
When the trailer harness is plugged in, the display
shows the brake circuit voltage. "0.0" shows when the brake pedal is released.
The color is user selectable - I chose orange to match the RAV4's radio display.
Here is some other stuff you may see. Step on the
brake pedal when parked, and after a few seconds the voltage will slowly ramp up
to a level about 30% of the max value set. It also varies according to inertial
braking forces when towing. Press one of the arrows and you can adjust the max
voltage to any level up to full battery voltage. This is how you fine tune the
brake behavior when driving with different loads or on loose surfaces. My little
trailer only weight 450 pounds empty, so the voltage is set way low normally.
Move the Manual Override lever below the P3 and you
anything up to get full (user set) voltage).
"Boost Level" (3 levels) determines how aggressively
the braking voltage ramps up. I left it set at "No Boost" for my little trailer.
When you step on the brake pedal with no trailer
cable attached, the display flashes a very annoying alternating red symbol and warning.
After a few seconds it reverts to the Tekonsha logo.
The "Help" mode provides several different useful
troubleshooting aids. This is the default blue display color.
Note: the P3 I won at a motorcycle ride had small scuffs on the display - they look far worse in the above pics due to the flash.
Tow Report: To follow, after I use the P3 a while over the 2008 Summer.
Update 06/09/08: The P3 is the "Next Generation" Prodigy, which many experienced RVers feel is the Gold Standard for this type of inertial controller. While it does a really decent job on smooth surfaces, it can't begin to compare to the hard-to-get Jordan Ultima 2020 for rough road or off road use: Jordan Brake Controller. I'm using one of these in my LX450 and it's the greatest! Unfortunately the new replacement "Plus" version with remote display has been under development forever.....
Price Alert!!: the P3 is sold everywhere for US$180+ but it CAN be found for less than US$120 with some Googling. Shop smart!
|
Updated June 09, 2008 |