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Trailer Wiring Harness

Hello. I have a 1998 Ford Explorer and Im looking to start towing with it. Im getting ready to buy a hitch for it but the truck doesn't have the wiring for the trailer to plug in. I probley need the 7 way plug because my trailer will have brakes. I was curious if there was a pig tail or anything I could buy a 7 way and plug into or does it have to be completely wired?

Thanks
 
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gijoecam

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Well, two things: First, for the lighting, there is a plug up under the driver's side taillight you can tap into. Unfortunately, for the brakes, you'll need to wire the truck for a controller.

-Joe
 
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Doug

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There's a 4 pin connector tucked up behind the drivers side tail light, if you look from underneath the truck it should be tucked up near the tail light. If you're towing a trailer with brakes on one axle all you're going to need is a 5 pin trailer connector, or 6 pin for two braking axles. You'll need a brake controller and you'll have to wire it in yourself, but if memory serves me correctly it's only 4 wires and it's not to bad to do.
 
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Nocturnall

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NICE, I figured there was no way ford would run those wires to the back if the vehicle didn't have a tow pkg. I don't think the trailer I'm looking to tow has brakes on either axle.
 
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terminator0723

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Heh. Im sure was a lot easier for Ford to just plug in the connector instead of running the wires when soemone wanted the tow package
 
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terminator0723

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FROADER

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This is what was on mine that has the "tow package"

The plug on the right is the one that connect to the plug on the truck behind the tail light. the left is the 4 pin dealio.

TowingWire.jpg
 
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tekrsq

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If you plan to pull trailers with brakes, then personally, I suggest installing a 7 pin plug. The majority of "bigger" trailers I have seen come with 7 pin wiring. I just think it would be easier to just do the install once instead trying to find a bunch of adaptors to fit a specific need.

I installed this plug www.southwestwheel.com/store/p-1153-multi-tow-74-adapter.aspx It has the 7 pin plug as well as a 4 pin incase you are pulling a smaller, "light duty" trailer. It will plug directly into your factory 4 pin plug, and all you have to do is run the brake contoller wire, aux wire, & battery charge wire. This website tells how to wire them correctly http://www.marksrv.com/wiring.htm
 
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terminator0723

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Oh yeah. Definately converting over to 7 way.. I gotta buy the connector for the 4way then buy a 4 way to a 7way adapter and run the other 3 wires into it..

But Im having a crazy time figuring out which connector i need to plug into the connector behind teh tail light....
 
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terminator0723

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HMM... I finally pulled the drivers side tail light off and pulled the cap off the connector and it had some corrosion in the plug... What can I get that out with?
 
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gijoecam

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Contact Cleaner, compressed air, and a wire brush. :)
 
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RV Wrench

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Your truck is not "factory pre-wired" for a brake controller, so you will need to hardwire the controller.

Here is what you do: buy about 30 feet of 10 guage wire (15 feet of one color and 15 feet of another, preferrably red and blue wires), two 30 amp auto-resetable circuit breakers (little silver boxes with a mount tab on them and two posts for the wiring), a handfull of wiring connectors, a 7-way plug for the back of your truck, and a brake controller. You will need to run one 10g power wire from the battery (+) through one 30amp breaker (which I usually mount to the firewall) and run that wire all the way back to the rear of the vehicle. This will be the charge line for the trailer's 7-way plug. I would use the red wire for that. Second, you will need to run another 10g wire (red again) from the battery (+) through another 30amp breaker, this time going through the firewall to the main power feed of the brake controller (usually a thick red wire on the controller). Last, you will need to run your 10g blue wire from the same brake controller location, all the way to the rear of the vehicle where you will install the 7-way (I usually go back through the firewall in the same location the power feed was routed). Now you have all your wires for hooking up the brake controller.

Dont actually connect your red wires to the battery (+) until all other wiring is absolutely completed. This will prevent shorts while you are working on the wiring.

The brake controller should have four wires. The first is a large red wire. Connect this to your power feed from the battery (+). The second is a large, usually white wire; this is the ground and should be connected to the chassis ground. There is usually a ground junction just under the dash somewhere that you can use. Third is the large brake wire which is usually blue. Connect this with your blue wire that you ran to the rear of the vehicle. Last, there should be a wire that is thinner than the other three that is marked as the signal wire. This will need to be connected to the brake pedal signal. In your vehicle, there are multiple wires coming from/to the switch at the brake pedal. Use a 12v test light and find the wire that energizes only when the pedal is depressed. I usually connect the brake control signal wire into this wire using a Scotch Lock connector. That should do it for your brake controller!

Now for the 7-way plug. I would advise you buy the 4-way plug in the picture above, plug it into your truck as recommended, and tap into those wires. This way you will not be cutting the factory Ford wiring, just the added harness wires. I would also advise you use heat-shrink butt connectors to prevent corrosion, or better yet, solder the connections and use heat shrink and electrical tape over the soldered connections. Last, I would advise you get a 7-way for your truck that has the wires already connected to it, not just the plug.

7-way wiring if you buy the one with wires already connected:
1) blue brake wire (connect to blue from brake controller)
2) black charge line (connect to red from the battery +)
3) white ground wire-run this from the plug straight to a ground point on the chassis

wires to connect to your 4-way harness pictured above:
4) right turn signal
5) left turn signal
6) marker lights

Other:
7) yellow wire for reverse lights - connects to the center pin of the 7-way, but is not needed if your trailer does not have reverse lights.

Check out this page if you need help with wire color codes: http://www.marksrv.com/wiring.htm
 
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terminator0723

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Great How- To! Thanks man... I bought the plug that plugs into the drivers tail light (for the 4 way) yesterday but i got home and realized they got me a plug for an older F-150.. So I took it back and he goes ' Oh I thought it work work...' So He ordered me the correct one and it's suspoed to be in today but they were closed when I got off work soooo...........
 
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