Strange trailer wiring problem - Diesel Forum

ncmech · 03-04-2007, 12:52 AM

Awhile back I spliced into the OEM wiring on my 05 super duty to install a 7 way plug in the bed of my truck for the truck camper. That plug has always worked.

Somewhere along the way, the rear 7 way and 4 flat connectors quit working. Picking up a toy hauler Monday, so I need trailer brakes and tried to fix this tonight.

The scenario:
Used the corrosion resistant scotch-lok connectors to splice into the wires along the bed rail. According to the wire color info I found online, I connected to the correct +12v, reverse, left turn, right turn, parking wires on the truck. I ran the ground from the new plug directly to the frame. Added another scotchlok tonight for the brake controller.

At the rear plug, I have +12V and trailer brakes. No signals, reverse, or parking lights. Thought I may have severed the wires using the scotch-loks, so I disassembled one and that does not appear to be the case. Connect a wire to the metal bus on the scotchloks to check continuity at the rear plug. Touching ground at the 7way rear plug shows continuity to ground, the signals, and the parking lights on the scotchlok bus bars. Touching the signal and parking terminals at the 7 way shows open to everything. I cant find any other connections between where I spliced in and the rear plug. The 4 flat plug isnt getting any power either.

I connected my buddy's 5th wheel plug to my in-bed plug to verify function. Everything worked fine, including the OEM brake controller.

Any ideas as to what is going on at the rear?

ch58dr · 03-04-2007, 01:47 AM

some trailers are wired different ,they don't use blue for the brakes ect .ect.. also ford an chevy wiring is different for trailers as far as location of pins. have to check the truck side with a test light make sure the fuses under the hood are not blown also. On the trailer side I usually take a battery charger an put the ground on the trailer then use a small nail or such, an put it in the positive clamp of charger an test the trailer plug wired an mark which wire lights up which lamps. you can then match it to your truck.

ncmech · 03-04-2007, 03:15 AM

The new plug I wired in the bed works fine. It's the OEM plugs at the rear that lost most of their function. The trailer has nothing to do with this- I'm using a meter to verify +12V on the truck and not getting it at the OEM rear plugs, but I am getting power in the bed plug I installed by splicing into these wires.

The connector behind the OEM plug is connected, the wires arent cut at the splice, and I still get +12V at the OEM plug, but no signals, brake lights, or running lights. This is the strange part of the situation...

budman451 · 03-04-2007, 03:24 AM

First, I would say to ditch the scotchloks. I have had so many problems with them here, they can drive you nuts with electrical gremlins. I used to use them, but after redoing so many connections, I found it was better to solder everything the first time. I would solder & heat shrink all of your connections. Otherwise, have you removed the connector at rear of the OEM plug and actually checked available voltage at the connector? I have seen where connections break in the plugs, and could cause your problem, altough small chance especially with no signal, tail, brake signals.

Buddy

STurbo90 · 03-04-2007, 03:42 AM

[ QUOTE ]

The connector behind the OEM plug is connected, the wires arent cut at the splice, and I still get +12V at the OEM plug, but no signals, brake lights, or running lights. This is the strange part of the situation...

[/ QUOTE ]

Not really, what I think happened is,

you spliced into to the "trucks" lighting wires, which is why the bed plug works,

the "oem trailer" plug (as part of the tow package) has its own set of wires, and thus fuses.

have you checked to see if the "trailer" fuses are good?

You say you still get 12V+ and Brake Actuator at the oem, but no turn/brake or running lights,

(the turn signals and brake lights are the same circuit/wire/position on the 7 way, so I'm not sure why you list them separately??)

those three terminals on the 7 way, left/brake, right/brake, running lamps all should have their own fuse in the fuse box,

since you say that they all show no continuity, and the wires are not broken anywhere, there must not be any fuses/or they are blown, otherwise you should show resistance to ground.

firesoutmatt · 03-04-2007, 10:55 AM

[ QUOTE ]
some trailers are wired different ,they don't use blue for the brakes ect .ect.. also ford an chevy wiring is different for trailers as far as location of pins. have to check the truck side with a test light make sure the fuses under the hood are not blown also. On the trailer side I usually take a battery charger an put the ground on the trailer then use a small nail or such, an put it in the positive clamp of charger an test the trailer plug wired an mark which wire lights up which lamps. you can then match it to your truck.

[/ QUOTE ]

Chevy and Ford use the same 7way . You can plug an rv into a chevy or ford and it will work.

ncmech · 03-04-2007, 11:29 AM

We have a winner! Finally figured it out a 3am this morning [hence the fact that I'm finally now dragging my lazy self outta bed at 10am]. Had the #9 20A blown under the hood and #38 20A blown under the dash.

Now I'm concerned about using that bed plug because I dont think it is optimum for the amperage of the truck+coach lighting.

The wires I spliced were colored per the codes listed on the marksrv site. Any idea what the correct ones are?