Trailer brake question

[Runningaford]

I know a lot of guys here run a trailers, and would have a trailer brake. I bought all the stuff for an aftermarket installation, but since then, through reading, found that many trucks came with a factory tow option....

I crawled under the rear end just now, and saw two connectors open, one with 4 prongs(female), another with 3 prongs(female). I also found the trailer brake 4-prong female plug under the radio, and at that point in the system, I've got 12 volt constant hot(+), ground(-), brake light signal, and a fourth which I'd presume goes back to the rear for brakes(I'll check the rearend connections tomorrow w/DMM).

In researching this for a while today, I read that you needed an additional 2 relays mounted on the side of the main power box under hood; which would connect to C105, and C149. I don't have the additional two relays.

In the reading I did, most said these additional two relays were needed, but one guy said that diesels(manual I presume) used relays within the main box? I've got two relays in the main box, but both aren't labeled as to what they supply.

I decided to ask, since the four prong female plug under the dash is energized, and working. Does this indicate I'm good to go, or perhaps with the two side relays gone, the P.O. bastardized something?

The thread where I was reading this is: http://www.ford-trucks.com/forums/1371503-factory-trailer-wiring.html

ifrythings
"Your truck is diesel isn't it? On the diesels the relays are in the under hood fuse box"

Thanks In Advance For Any Suggestions!

 

[ironworker40]

That fist the diagram in that other forum post is for gasoline engines.
Diesel engines the relays and fuses are in the under hood fuse box. Your owners manual will have a picture of this fuse box and tell you what they are for.
My 1993 book lists as follows:
relay #1 trans #2 trailer backup lamps #3horn #4 trailer tow /dual wheel running lamps ( i assume these are the ones on the rear fender a dually) #5 trailer battery charge

fuses #4 25amp trailer backup and running lamps #5 15a trailer battery charge relay speed control backup lamps daytime running lamp (canada only) #6 5a RH trailer stop /turn #7 5a LH trailer stop/turn

maxi fuses #18 30a trailer battery charge #21 30a trailer brake feed
the lid on the under hood fuse box should show you the positions of the fuses and relays as well as your owners manual

 

[ironworker40]

4 prong plug under radio wire colors should be as follows:
red power to aftermarket brake controler
black ground
light green brake switch input
dark blue tailer brake feed to rear of truck

 

[ironworker40]

In the rear under the bumper there should be 2- 4 prong plugs for trailer wiring
wire colors are:
dark green right turn
yellow left turn
brown/white running lamps
black ground

other plug wire colors:
dark blue trailer brakes
orange trailer battery charge
red/white trailer back up lamps
4th pin I can't locate, it may be unused

Now you wire in an rv style trailer plug if you don't have one (if you do check it to see if it is wired correctly, some of them have the diagram on the lid that covers the terminals), install your brake controller under dash and your good to pull any trailer that has an rv style plug and you can get a 7pin rv style to 4 pin flat for smaller trailers, assuming no one butchered the trailer wiring.

 

[Runningaford]

Sweet, and thank you. I figured I'd ask, as it all looked complete, funny that from what I found didn't cover diesels; hopefully this will help others

 

[Runningaford]

One last question, since the diesel is different, and all relays originate from the under hood fuse box, does that also mean the wires are contained in the main wiring loom headed to the rear? Or does it still go out through the C105, and C149 auxiliary looms?

The backend doesn't look adulterated, but the plugs according to the local ford dealer, says they're obsolete; no biggie, I'll just splice the wire. The #4, and #5 relays aren't in the box; the #5 doesn't socket doesn't have any metal contacts in it; so it doesn't look like it'll work at all. The correct size fuses are in place.

I'm gonna splice all of this in, and see where I'm at.

 

[ironworker40]

#5 relay is not neeed most of the time anyway. But it does control other options that i assume you dont have.
#4 is for running lamps so you must have that one
As far as the wires all being in one i dont know
This is all from a 1993 ford book so you have a 92 and 94 so they might be slightly different.

 

[Runningaford]

Follow up, the #1 relay slot is the 12v hot for towed battery charging, and my #4 are the lights. I bought two Duralast relays at Autozone, and presto, all works! The rear female adapters were there, but after checking around, I got the word from Ford that the connectors were obsolete; so I cut, and spliced into the wires. The coloring noted above was absolutely correct; minus the grounds; which were white.

I appreciate the help Ironworker

 

[ironworker40]

Happy to help. Like I said my info was from a 1993 book so i guess there are some differences. Glad it all worked out. Did you install brake controller? Have you ever used one? I only used time delayed controllers with digital readout, mine goes from 0-10. There are proportional controllers also. On these trucks and others with marginal brakes, such as my buddies motor home, I like the sys setting on so the brakes come on slow, this way the trailer brakes aren't slamming on trying to stop the truck by themselves, overheating them. Then I take the trailer out empty and do several stopes increasing the power output setting to see if I can get them to lock up or feel them pulling ******* the truck. Then say they lockup on 5 on the readout (arbitrary numbers). I would back off them to say 2 and use this for an empty or lightly loaded trailer. If I had a trailer that was loaded to the max I would run 8 or 9 as long as it is not locking up. If you can't lock them up with an unloaded trailer, the trailer brakes need attention. Another thing I do is if I am in heavy stop and go traffic that is stop and go I will back them down so they don't keep pulling and jerking. If it is the middle of the night and I'm at highway speed I turn them up, this way if I have an emergency stop, such as a deer in the road I have maximum braking.
If your trailer gets a sudden sway from wind or road conditions you can apply just the trailer brakes and it will stop the sway, thats why I only run controllers that have this option of applying just the trailer brakes.
If you are on slippery roads, such as gravel, snow or wet roads, lower the output so they don't lock up. Locked brakes not only destroy tires but it takes way longer to stop.
When I use trailer brakes on a vehicle with really great brakes, such as my buddies super duty with 4 wheel disc I will set the sys so the trailer brakes come on faster. All other adjustment will be the same.
Bottom line is match your braking to the vehicle and trailer weight, and road conditions.

 

[jhenegh]

Happy to help. Like I said my info was from a 1993 book so i guess there are some differences. Glad it all worked out. Did you install brake controller? Have you ever used one? I only used time delayed controllers with digital readout, mine goes from 0-10. There are proportional controllers also. On these trucks and others with marginal brakes, such as my buddies motor home, I like the sys setting on so the brakes come on slow, this way the trailer brakes aren't slamming on trying to stop the truck by themselves, overheating them. Then I take the trailer out empty and do several stopes increasing the power output setting to see if I can get them to lock up or feel them pulling ******* the truck. Then say they lockup on 5 on the readout (arbitrary numbers). I would back off them to say 2 and use this for an empty or lightly loaded trailer. If I had a trailer that was loaded to the max I would run 8 or 9 as long as it is not locking up. If you can't lock them up with an unloaded trailer, the trailer brakes need attention. Another thing I do is if I am in heavy stop and go traffic that is stop and go I will back them down so they don't keep pulling and jerking. If it is the middle of the night and I'm at highway speed I turn them up, this way if I have an emergency stop, such as a deer in the road I have maximum braking.
If your trailer gets a sudden sway from wind or road conditions you can apply just the trailer brakes and it will stop the sway, thats why I only run controllers that have this option of applying just the trailer brakes.
If you are on slippery roads, such as gravel, snow or wet roads, lower the output so they don't lock up. Locked brakes not only destroy tires but it takes way longer to stop.
When I use trailer brakes on a vehicle with really great brakes, such as my buddies super duty with 4 wheel disc I will set the sys so the trailer brakes come on faster. All other adjustment will be the same.
Bottom line is match your braking to the vehicle and trailer weight, and road conditions.

He said it perfectly