Ground Problem - Stumped

[jdwilson]

Was getting ready for a weekend trip up the coast. When I went to test the electrical between my GMC truck and Forest River Roo trailer (7-pin), the front running lights on the trailer illuminated, but the rear running lights, turn signals, and brake lights did not. So far, using a voltmeter, I checked the power coming from the truck and found that the left turn signal fuse was blown -- I changed that out. At that point, I had a great signal from turn, running and brake lights coming from the truck. When connected however, no change. Next, I located the ground wires coming from the back end of the trailer. They were bundled and bolted to the trailer frame. I separated those and cleaned them up and bolted them separately to the frame -- again, no change. Next, I located the ground coming from the trailer harness (harness is fairly new). This was bundled with two other grounds headed towards the back of the trailer and was grounded to a screw in the box that was bolted to the frame. To test this connection, I separated the wires and grounded them to a provisional ground that I drilled-out and connected to the frame -- very clean. Still no change. One other thing, when the trailer is connected to the truck and I hit the remote lock, the rear lights faintly illuminate momentarily. I am at a loss of what to do next.
Help.

[da_bees]

Taking your word that;
A.No wireing has been done since lights worked properly.
AND
B.You made good contact between all wire bundels you spoke of.

Ground test method #1
With 7 way pluged in, park lights on,either turn signal on and vom set to dc volt,black probe to tv frame and red to trailer frame. If any voltage is detected,ground is weak between tv and trailer.

Ground test method #2
7 way pluged in,no lights on and vom set to ohm/R,either probe to good ground on tv and other probe to trailer. Anything above fraction of ohm reading is weak ground between tv and trailer.

If either or both tests above show weak ground,test as follows.
No lights on and 7 way unpluged. Test between #1 in tv 7 way and tv frame. Anything above fraction of ohn means #1 has poor contact to tv ground.

Same test as above between trailer 7 way #1 to trailer frame.

If any test above fails and you are unable to find the bad connection,post back and somone will walk you through locating the trouble spot.

[wa8yxm]

I used to have issues with the ground on the tow vehicle side in my trailer days.

NOTE: those testers are good, but often they will NOT detect a bad ground, They draw a very low current (few thousands of an amp) and your tail lights may draw several amps (Several THOUSAND times as much power as those LED testers)

[dougrainer]

IF your other lights function, your GROUND is NOT the problem. Your problem is probably where they wire nut'd the clearance light wires at the a frame area of the trailer. Follow the 7 way trailer wire and where it enters the RV or junction box, verify all the GREEN, wires are in the bundle. Doug

[Bob_Olallawa]

jdwilson wrote:
Thanks. Silly question, how do I check for the ground on the truck side? Yesterday, after I changed the LT signal fuse, I grounded the voltmeter to the truck frame and tested the LT, RT and brake signals and got strong readings. Does this tell me the ground is fine from the truck? Or do I need to do another test?

Use the ground spade in the plug for ground and any hot spade in the plug to see if it is grounded properly

[RoyB]

I take the guess work out of the truck side by using one of these 7-way TEST PLugs. These are available from etrailer where I got mine but I think the local auto parts store will carry them as well...



I carry this in my RV tool box. If it turns on the proper LEDs on the adapter on the truck side when plugged into the 7-wat trailer connector then the problem is on the trailer side.

I also spray WD-40 into the trailer connector everytime I use it. I will squirt some WD40 into the the 7-way connector then plug in the trailer plug and move it around good a few times then lock in place.

My 2010 Ford trailer connector is only active when I have my ignition key turned on. Trying to measure the spade lugs with my multimeter was awkward for me to do so I just picked up one of the adapters to test it. It plugs right in and i can look at all lights modes at the same time.

Roy Ken

[jdwilson]

Thanks. Silly question, how do I check for the ground on the truck side? Yesterday, after I changed the LT signal fuse, I grounded the voltmeter to the truck frame and tested the LT, RT and brake signals and got strong readings. Does this tell me the ground is fine from the truck? Or do I need to do another test?

[sch911]

Check the ground from the seven way to the frame on both sides...