Electric Brake Control for Subaru Forester

[Todd Sleeman]

Hi-
Sorry for all the questions. First post, and this is all somewhat new to me. I'd rather get the correct info upfront than go ahead and do this THEN learn the easy way.


I'm in the process of getting an electronic brake control for my '03 Subaru Forester. A few questions:

Any recommendations on the model to get?
Any reccommendations on where to mount the unit? I've looked at the clearance between my legs and under the dash and there just isn't a lot of room. I assume you want to have easy access to it for adjustments and whatnot.

Any tips on wiring it up? I've got a direct line from the battery to spare tire well that controls our marker lights for the 4-pin trailer hook-up. Is it easier to run this line back up to the front or is there an easy route through the firewall? Also, what is the easiest way to tap into the brake lights? I found the switch by the brake pedal, so I'm assuming this is the spot.

One more question: What is the minimum gauge wire that you need to run from the car battery to the trailer battery, and is it necessary to have some sort of circuit breaker between the two?

Thanks,

Todd

[Frederick L. Simson]

I'd rather get the correct info upfront than go ahead and do this THEN learn the easy way.

Can you get someone else to do it? That would be "the easy way" in my book...

sorry... That's what I did.

In my pigtail with the molded on 7-pin connector, The (White) Ground wire and the (Black) charge line are each 10 gauge. I would take that to be the minimum.

[Per Walthinsen]

Todd:
I've used a couple of different electronic brake controllers, and the Prodigy by Tekonsha has been by far the best, in my experience. Because it is not sensitive to fore and aft leveling it also lends itself to less than permanent mounting.

The charge and ground wires should be at minimum 10 gauge. If you need serious charging 8 gauge and even 6 gauge would be beneficial.

[Bob Cupp]

Todd-Do you have a standard 4-pin trailer connector or an extra one that you are hooking your markers up with? The standard connection should have the markers come on with the tail lights of the car.
White wire=ground
Brown=tail lights/marker lights
Yellow-left turn signal/brake
Green=right turn signal/brake

If your car has seperate turn signa/brake lights you would need to get a converter that combines the turn/brake function. I recently found a great one made by Hoppy (Hopkins) at Wal-Mart for about $14. It looks like a slightly overweight 4 pin connector but has the solid state converter built in. Mine works great without a bunch of rewiring.

[Brian B-P]

I assume you want to have easy access to it for adjustments and whatnot.

Yes, I think that's important. It is an addition to the operator's controls of the car, and should be reachable and visible without difficulty like the rest of them.

I've got a direct line from the battery to spare tire well that controls our marker lights for the 4-pin trailer hook-up. Is it easier to run this line back up to the front or is there an easy route through the firewall?

I can't think of any of the four wires in a 4-pin trailer hook-up which are useful for the brake controller: the combined stop/turn lights are not the brake signal you need, there is no power source, and the ground connection is too indirect and very likely much to small.

Even if there is not an easy route through the firewall, that's where you need to go, with power and ground wires (normally black and white). The brake signal is just under the dash area, and the output (normally blue) can go to the back either inside or outside of the car (I went back out the same firewall hole as used for power, and then to the back underneath).

Also, what is the easiest way to tap into the brake lights? I found the switch by the brake pedal, so I'm assuming this is the spot.

That's the normal approach, and it is what I did.

[Chris C]

I took the easy way out! I bought a Prodigy Brake controller online and saved enough to pay a professional to install it and wire everything for my trailer. I didn't even have to get my hands dirty!!!!! It's done correctly and any problems will be tended to by a professional......................which I'm certainly not when it comes to wiring.

[Marv]

Todd,
Maybe I can summarize, without going into too much detail.

If your Subaru has the factory (or factory-like from third party) trailer wiring, you have everything you need, including the power converter, to control the lights on the trailer.

You need three (or two) more wires: one heavy-guage from the battery, through a circuit breaker, to charge the trailer battery. Another wire from the battery through the brake controller to the trailer to operate the trailer brakes. Finally, a wire from your backup lights to the trailer backup lights. This one is optional.

Thus, seven circuits, four you have now plus these three. You can get a 4-to-7 connector for the car. Plug your four-wire flat connector into the back of it and then run the other three wires in the car. Then, it will be ready to connect to the trailer connector.

Marv

[Brian B-P]

And the two connections which Marv didn't mention, presumably since they don't extend to the trailer: the brake controller needs a good negative (ground) connection, and the brake signal (from the pedal switch).

Finally, the "ground" connection in the four-way lighting connector is inadequate for either battery charging or electric brake operation, so the 4-to-7 converters (such as the one I use), only use three of the wires from the 4-pin socket, and have separate wires for the three additional circuits which Marv listed, plus a separate ground wire, much heavier than the one in the 4-pin socket.

[Byron Kinnaman]

And the two connections which Marv didn't mention, presumably since they don't extend to the trailer: the brake controller needs a good negative (ground) connection, and the brake signal (from the pedal switch).

Finally, the "ground" connection in the four-way lighting connector is inadequate for either battery charging or electric brake operation, so the 4-to-7 converters (such as the one I use), only use three of the wires from the 4-pin socket, and have separate wires for the three additional circuits which Marv listed, plus a separate ground wire, much heavier than the one in the 4-pin socket.

I would think this would be a case by case thing. I wouldn't want to make a generalization about current carry capabilities or needs. You could be right about needing a larger wire, but a larger wire could already be in tow vehicle connection.

[Brian B-P]

... a larger wire could already be in tow vehicle connection.

I assumed (perhaps incorrectly) that we're talking about the common 4-pin flat connector here. Even if huge wire is attached to it, this "bullet" contact is not good for reliably carrying much current, and the brakes need at least several amps in addition to the lighting plus any battery charging current (it all returns through one "ground" connection). I agree that a generalization may be inappropriate, but the 4-to-7 adapters do typically use a separate ground connection for this reason.

I think if the tow vehicle is wired for high current on the negative wire, it is likely to have full charge-and-brake wiring with a 7-pin connector (like a typical modern "prewired" pickup truck or large SUV), not a 4-pin lights-only connection.

[Todd Sleeman]

Hi Guys-
Thanks for all great info! I am definately following the thread.

Does this sound reasonable:

I'll be hooking up the brake controller to the positive (with a breaker) and negative of the battery with 10 gauge wire and tap into the brake switch, then I'll be running 10 guage to 'brake' line on my new 7 pin connector. I didn't get an adaptor, but will tapping into the existing 4-pin connector wires for directional only. I'll also run a 10 guage wire from the battery to the charge line of the 7 pin.

In regards to ground, can I use the heavier wire of the 7-pin and just ground to the car frame or should I run a wire back up to the negative of the battery (or is that a big no-no)?

Also, should I install a breaker between the hot-line of the battery and the 7-pin to isolate the car battery from the trailer battery or is there no reason to do this?

Thanks!

Todd

[Brian B-P]

In regards to ground, can I use the heavier wire of the 7-pin and just ground to the car frame or should I run a wire back up to the negative of the battery (or is that a big no-no)?

The car's body is likely quite capable of handling the current, but the connection to it is less certain. It can be done either way (separate wire or via the body), but I chose the separate wire.

This could start a long debate, as there are strong proponents of each approach.

Also, should I install a breaker between the hot-line of the battery and the 7-pin to isolate the car battery from the trailer battery or is there no reason to do this?

A circuit breaker is definitely called for to protect against excessive current due to a short circuit.

A relay (or solenoid) can also be added to shut off power when the car is not running; I think this is a good idea and I put one in.

[Byron Kinnaman]

I assumed (perhaps incorrectly) that we're talking about the common 4-pin flat connector here. Even if huge wire is attached to it, this "bullet" contact is not good for reliably carrying much current, and the brakes need at least several amps in addition to the lighting plus any battery charging current (it all returns through one "ground" connection). I agree that a generalization may be inappropriate, but the 4-to-7 adapters do typically use a separate ground connection for this reason.

I think if the tow vehicle is wired for high current on the negative wire, it is likely to have full charge-and-brake wiring with a 7-pin connector (like a typical modern "prewired" pickup truck or large SUV), not a 4-pin lights-only connection.

Be careful of assumptions, sometimes they're not correct. I don't know the current carrying limit on bullet connectors, but I can tell you they are designed to accept up to a 10 AWG wire. The biggest problem with any bullet connector, including 4 and 6 circuit flat connectors used in trailer applications is connect and disconnect forces. They take a lot of force to get fulling connected and a lot of force to get disconnected.

I went to Tyco's web site and discovered that maximum wire size of 10 AWG is wrong. The maximum wire size is 8 AWG.



Edited for added information.

[Todd Sleeman]

A circuit breaker is definitely called for to protect against excessive current due to a short circuit.

A relay (or solenoid) can also be added to shut off power when the car is not running; I think this is a good idea and I put one in.

More great info! Would a 30A be an appropriate size for the circuit breaker? Any recomendations on relay/solenoid brands? Any wiring tips that aren't obvious?

Thanks again,

Todd

(figure I should get the car wired right the first time, then work my way back to the trailer...)

[Byron Kinnaman]

Todd,

I have a tendency to get a little worried when somebody asks a lot electrical questions. Wiring is one of those things that appears to be easy to do, kind of like plumbing. However, if not done correctly large problems can ensue. Costly damage can be done to either or both the trailer and the TV. I therefore suggest that you take the TV to an RV or Trailer shop and have at least check it, better yet is let them do it. You might be money ahead in the long run.

I work with electricity stuff for a living, including vehicle electrical components. Even with the knowledge and understanding I still took my TV to an RV shop to get it wired for the trailer. Several reasons for this;

1. If I make a mistake and kill something in the TV or trailer, they have to do the repairs.
2. They know or should know where the best connection spots are.
3. I don't like crawling around under vehicles any more.

If you like crawling around under vehicles then forget number 3.

[Brian B-P]

Would a 30A be an appropriate size for the circuit breaker?

That's what I picked, since it is a generally accepted maximum continuous current rating for the 10 gauge wire which I used. I have no idea how much current actually flows in my setup under driving conditions.

Any recommendations on relay/solenoid brands?

I don't have any brand recommendations, but for the relay/solenoid type...

A common style (usually what you get when you ask for a "solenoid" in a store) is a hefty device which looks like the external (not built onto the starter) solenoid for starting a car. I suggest making sure that it isn't actually a starting solenoid, which is designed to handle very high currents for very brief periods, but rather a "continuous duty" device, designed to take a more modest current but stay on indefinitely. Auto parts stores, should have the starter units readily available, but might not even know about the continuous-duty units; on the other hand, RV supply stores routinely have buckets of the continuous-duty units on the shelf.

Some members have pointed out here that there are much more compact relays which are still good for 30A continuous duty; I would likely consider this type if I had to do it again, and would try industrial or automotive supply stores for them.

[Brian B-P]

I don't actually enjoy crawling under vehicles, and truly dislike contorting my way under dashboards; however, I did find the time spent under my van to do the wiring interesting and informative.

Perhaps more importantly, I have more faith in my ability to understand and properly implement this type of system in my van than I do in some stranger in an RV repair shop. Having seen the work done in vehicles by auto sound and accessory installers, and in RVs by the manufacturers, and having no reason to believe that any RV shop would be any better, I have low expectations of their work.

If you work on your own brakes, you might consider yourself capable of taking on a similar responsibility in the wiring area. On the other hand, most vehicle maintenance work does not involve design decisions, as this wiring does. Everyone need to make their own decisions; in my case, there's almost no part of a vehicle which I have worked on (not all on the same vehicle), and I installed both the trailer wiring and the rear suspension air bags in my otherwise dead stock and nearly new van.

[Byron Kinnaman]

I don't actually enjoy crawling under vehicles, and truly dislike contorting my way under dashboards; however, I did find the time spent under my van to do the wiring interesting and informative.

Perhaps more importantly, I have more faith in my ability to understand and properly implement this type of system in my van than I do in some stranger in an RV repair shop. Having seen the work done in vehicles by auto sound and accessory installers, and in RVs by the manufacturers, and having no reason to believe that any RV shop would be any better, I have low expectations of their work.

If you work on your own brakes, you might consider yourself capable of taking on a similar responsibility in the wiring area. On the other hand, most vehicle maintenance work does not involve design decisions, as this wiring does. Everyone need to make their own decisions; in my case, there's almost no part of a vehicle which I have worked on (not all on the same vehicle), and I installed both the trailer wiring and the rear suspension air bags in my otherwise dead stock and nearly new van.

Brian,

Like I said earlier, when somebody asks a lot of questions about wiring and (which I didn't say) the type of questions asked gives an indicator of their ability and knowledge, it might be time to have somebody that does have the knowledge and insurance to handle it. That's not meant as a negative just the facts.
Whether you have or think you have the knowledge is irrelevant to case at hand. We have a member that is struggling with wiring and wrong advice could cause him a lot of problems. It would be best for him to at a minimum have what ever wiring he does check by somebody that does have the knowledge.

[Brian B-P]

Anyone who is planning on paying someone to wire their vehicle for a trailer, counting on them to know what they're doing, might want to ask a few questions...

• Have they installed this equipment in this model of vehicle before? (if not, they really don't have the knowledge you're counting on; will they acquire it?)
• Where will the brake controller be installed in this specific vehicle? (I have asked this and been given unsafe and unworkable positions)
• Will you accept responsibility for damage to vehicle systems resulting from errors in the installation? (I wouldn't assume this)
• How much current is the system intended to carry to the trailer? (ensure that what they are providing matches your intended use)
• When the tow vehicle is shut off, but the trailer is still connected, can the trailer's refrigerator run down the tow vehicle's battery? (this establishes the capability they are proposing to install, without getting into the details of the design)

These are the sort of questions I essentially asked myself, by considering these (and other) factors in making my choices.

Answers like "don't worry about it... we've done this for hundreds of customers" don't reassure me at all, especially when I realize that not one of those customers had the same type of controller or similar vehicle, and the guy who will be actually doing the installation started last week and has no training.

You could instead, of course, blindly trust... but I wouldn't.

[Marv]

Brian,
That is a really good set of questions to ask. In this case, virtually no shop has done this installation on this vehicle. (There was a poster on one of the Scamp forums who was towing with a Forester; that is the only one I have heard of.) So the honest technician will admit this is virgin territory.