trailer connector problem

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dtoots1
350 crawler
350 crawler
Posts: 1160
Joined: Fri Nov 30, 2012 8:54 am
Location: akron, ohio

Re: trailer connector problem

Post by dtoots1 » Tue Apr 07, 2020 2:45 pm

does not work..no running lights....

now i checked again with key on and trailer not plugged in i pick up light on tester with turn signal on...only by touching my probe to the five o'clock pin.....and as always am looking into the trk connector from the rear...why is five o'clock working...is that supposed to be the ground....
how the devil do you really check for actual ground by itself???

i need the proper ground.

Jim B
350 crawler
350 crawler
Posts: 2072
Joined: Sun Nov 05, 2017 11:36 am
Location: western Maine

Re: trailer connector problem

Post by Jim B » Tue Apr 07, 2020 4:20 pm

If using a test light there should be no light if you ground the test light lead to bare metal on the trailer hitch frame and touch the probe to the socket blade. A voltmeter should show no voltage between the blade (+ lead) and frame (- lead). If no voltage shows a check with an ohmmeter should ideally show zero resistance between the two points.

You say no running lights. Please clarify for me if by running lights you mean tail and any side or rear marker (running) lights. Or if the tail lights work but not the side and rear markers. Just want to be sure we are calling the lights by the same names.

Turn on the truck 4 way flashers, parking lights, Key in run position but engine not running ( that should make the aux power live), transmission in reverse and see which terminals do not show power. The ground should be the only one dead. The brake power might show a signal as the computer will likely be trying to check the brakes. Use the bare spot on the hitch frame to ground your light or meter for this check.

dtoots1
350 crawler
350 crawler
Posts: 1160
Joined: Fri Nov 30, 2012 8:54 am
Location: akron, ohio

Re: trailer connector problem

Post by dtoots1 » Wed Apr 08, 2020 6:25 am

well guys,
thanks to JimB and his excellent advice, this a.m. was able to find out that the ground on my truck is at the 5 o'clock and the aux is at 7 o'clock. Simply have to hook up wire to positive side of battery to find ground (number 5o'clock blade is only one producing light connected to battery positive side) and negative side to find live blade, which is only 7o'clock. GMC has the truck connectors upside down with door flap opening down and not up.
now if i can determine where all these others get hooked up maybe can get er done. Earlier testing shows me that 3o'clock is my left turn signal and 9 o'clock is the right turn signal, now it is possible that i may have a blown fuse yetl but visual inspection of the trailer brake fuse appears to be ok, since these 30am square fuses do not have any test points, will find out as i progress. Now my test light hooked up to battery ground produces light at the 7 o'clock blade and i have to assume that is aux. Now testing turn signals shows that 3 o'clock is left turn and 9 o'clock is right turn

Now comes a bit of weird. turning the key on to test for running lights output at the truck connect with ground test hooked to battery,
i do not get test light at11 o'clock pin and do at 5 and 7 o'clock....If 5 o'clock is ground with key off how is it getting light with key on??

so here is what we have listed..

3 o'clock is left turn
5 o'clock appears to be ground
7 o'clock is aux
9 o'clock is right turn
center pin is backup

need to determine what feeds are 11 o'clock and 1 o'clock.

it kinda seems it may be wired upside down kinda backwards on the truck connection can anyone figure out if that is true?
Last edited by dtoots1 on Wed Apr 08, 2020 7:02 am, edited 1 time in total.

Jim B
350 crawler
350 crawler
Posts: 2072
Joined: Sun Nov 05, 2017 11:36 am
Location: western Maine

Re: trailer connector problem

Post by Jim B » Wed Apr 08, 2020 7:02 am

Gee, you could have told me it was mounted upside down before this. LOL

dtoots1
350 crawler
350 crawler
Posts: 1160
Joined: Fri Nov 30, 2012 8:54 am
Location: akron, ohio

Re: trailer connector problem

Post by dtoots1 » Wed Apr 08, 2020 8:11 am

well guys...that is exactly what they at gm did....if you draw a clock diagram and place wiring aux at 1 o'clock right turn at 3 o'clock, brake at 5 o'clock,ground at 7 o'clock, left at 9 o'clock and running lights at 11no'clock....now turn the clock to your left placing 12 o'clock at 6 o'clock position and it is correct for gm hookup and campers and goose...

no one on the internet ..not even gm bloggers ..mention that at all!!

gotta b e unique!

and thanks to all for the fun!!! and help!!

by the way i never even thought it mite make a difference in hookup.

Ray III
2010 crawler
2010 crawler
Posts: 609
Joined: Sat Aug 25, 2007 1:39 pm
Location: Troy, NY

Re: trailer connector problem

Post by Ray III » Sun Apr 12, 2020 5:50 am

You are better off plugging in your trailer connector and then noting what colors do what functions on the wires coming out the end of the cord. This cord should be going into a junction box that lets you move an eye terminal to the correct stud with the trailer wiring on it.

I found the brake by holding the trailer brake switch closed with an object. I also did the same as you and ran a separate ground to the brakes to make them reliable (2 wire boat cable from junction box to brakes).

dtoots1
350 crawler
350 crawler
Posts: 1160
Joined: Fri Nov 30, 2012 8:54 am
Location: akron, ohio

Re: trailer connector problem

Post by dtoots1 » Sun Apr 12, 2020 6:42 am

the problem literally is that my GMC reads the connector itself and the biggest issue was finding the actual ground pin...even with 1 or several wires not connected to the trailer plug the truck shows up error on trailer connector circuit. so until i found the actual ground pin and turn signal pins could not see the pattern. once can see pattern it was simply move the clock around. course it makes sense then just what was needed..

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