View Full Version : Diffuaculty wiring 7 waytrailer hitch wiring 07 trailblazer

04-28-2018, 09:39 AM
Diffuaculty wiring 7 waytrailer hitch wiring 07 trailblazer

I have a 7 pin round tail/brake/blicker/anti brake reverse all I can manage to get working are the right/left brakelight/blicker canít get the taillights on.

Hereís what Iíve connected all from trailer end plug.

pos1- ground black

pos7 trailer antireverse lockout. black
pos5 green
pos2 yellow

Pos3 tail light brown from yellow/green
I do have continuity on my wiring, and Iíve checked all the fuses under the seat all have continunity.
Not yet checked at the underhood fuse block thereís these associated w/ trailer
4 Back-Up-Trailer Lamps
32 Trailer

Additionally I have removed the radio circuit fuse the NAV unit took a dump and created a major drain 3.3amps on battery I could reinstall the fuse since radio unit is removed maybe the taillights go though the radio circuit.
Thanks for any helpful advice

04-30-2018, 11:03 AM
Brakes lights/blinkers work Can’t get tail-lights to come on

I have a 07 trailblazer it has a 7 pin round trailer plug I have the male end at the trailer.

I’ve managed to get the brake lights and blinkers working however the tails won’t come on.
I have checked all fuses under the hood and under the rear seat all have continunity.

I inspected the wiring under the car and they appear fine I don’t want to rip the carpeting and rear seat out to trace a wire.

Been informed that I can’t tap into the cars taillight wire because it would overload the circuit.

I have wasted way to much time messing w/ the none tail light issue.

I sometime trailer in the dark so it would be good to have sometype of red light back there.
All I can resort to w/ this car is battery operated taillights.unless anyone has usefull advice.

05-01-2018, 08:29 AM
Have you established that when your truck lights are on you have 12 volts at pin 4 on the truck side of the connector? If not, do so.

If you do have 12 volts there, then plug in the trailer and see if you have 12 volts coming out of the back end of the trailer connector. Use a small probe on your voltmeter to do that.

If you have 12 volts coming out of the trailer connector then check for 12 volts at each of the tail lights and running lights. If not, check your grounds. Over 90% of light problems on a boat trailer are due to faulty ground wiring. Usually, boat trailers are wired to use the trailer frame as the ground. That has high potential for problems. It's best to run separate ground wires to each light.

On some trailers, the running lights are daisy-chained, so you need to check each of your running lights for broken wires or disconnection.

If you do not have 12 volts at pin 4 on the truck, pull off the connector and test whether you have 12 volts coming to the back of the connector for pin 4. If so, repair or replace the connector. If not, then you need to track down there that wire is disconnected. It will often be at the fuse box, so you will need to get get out your truck manual and find what fuse controls that circuit. If not at the fuse, then run a separate wire from the fuse to the connector on the back of the truck, bypassing the existing wire.

05-01-2018, 11:40 AM
since each tail light has it's own ground and the fact that the brakes/blinkers work wouldn't that indicate good grounds?

I will crawl under there w/ headlights on will test pin #4 and report back.

05-01-2018, 01:50 PM
It should indicate a good ground to the socket. Are you dealing with bulb lights or LED's? If bulbs, check to make sure one bulb performs all three functions - light, blinker, stop. It's possible that you have two bulbs in there, but haven't seen one of those for a long time. Pull them and use emery cloth on the contacts.

05-01-2018, 02:16 PM
update pin#4 the big blue wire on vehicle no voltage w/ lights on.

I checked the big red and didn't get voltage there either I did get continuity on big white wire to the frame of car.

the big spade part of the second part of the OEM coupler was covered w/ about 50% rust attach image I scraped w/ screwdriver and sparyed soaked in CRC electronic cleaner.

I actually have a combination of LED and just incandescent regular so the possibility of the taillight filament being burned on the regular is slim.
2nd actually I have reversed the lights so I would rule out filament being burned or could the LED possibly have separate taillight lights?

05-03-2018, 02:13 PM
The first diagram scares me to some extent......

first off, you need the tow package to get full functionality out of a 7 pin connector on the truck -

second, I'd suggest you use a battery and a couple jumpers and verify the trailer wiring - for colors and integrity....not everybody uses "the standard"

Then, verify the desired functions on the truck and note their location(s) on the connector pins

Ideally, the "color standard" will have been followed and the pin utilizations as well...if not, one side will have to have wires relocated to match the other.

The benefit to using the 'standards' is knowing the hookup will work the first time you plug things together.

Finally, to remove ambiguity, one typically has to specify the connector orientation on a pin out diagram as things get mirrored when you look "from the other end".

05-03-2018, 04:25 PM
I will inspect trailer fuse #42,w/ lights on/off will check voltage on this circuit.

not giving up but I have inizuated
new plan B glue 12" 12VDC red LEDs stripes on stern for taillights powered w/ boat battery will also get amber LED stripe for side markers.

both glued to hull I think the aft. LEDs will add enough light for night fishing/netting + I have taillights. hope the brake lights are brigther than LED tails.

Bt Doctur
05-07-2018, 10:17 PM

05-08-2018, 06:30 AM
yes the only way I can just get the brakes/blinkers to function is the 7way traidtionale.

there are a few things since initial 7pin trailer end plug was installed. first I restripped the wires exposeing 2" of bare wire then I did the haywire twist around the securing bolt then add the squared washer I certainly have a secure electrical conncetion.

been getting conflicting infor about trailer end pin # 1 O'clock position power I'm not sure if I don't need power on this pin I think I don't because there's nothing on the trailers end to power or am I missing something here?

I don't have power on pin #1 O'clock position car end.

each tail lights grounds come from trailer end pin # 7 O'clock I added a extra ground from the trailers frame the taillights will hopefully function will the extra ground interfer w/ the pin #7 O'clock connection

I wasted way to much time on this so if the improvements don't resolve the no tail lights I procedeed to plan B
glue red LED stripes on stern wired direct to boats battery.

thanks for link stuff appears differnt on bing compared to google. STB

05-08-2018, 09:36 AM
If it was me i would just put a new set of lights on the trailer. As far as the trailer overloading the running light circuit is a crock. At most all you need is a larger fuse in the truck. Your issue sounds to me at the wires on the truck. Trace the connector on the truck to the wire loop how is it connected? Depending on the year and make there should be a tee get a new trailer wire kit and plug it in they are vehicle specific. What is the year and model of your truck?

05-08-2018, 12:03 PM
Why would I just put a new set of lights on the trailer the brake lights and blinkers work fine.would be nice to have taillights.

07 Saab 9-7x 5.3i AWD there are other circuits on the same as taillights if the trailer sucks up all voltage other stuff on car will sease to function correctly.

I have np voltage on pin #4 at car end.