Trailer lights not working
10-20-2014, 05:17 PM
#1
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Trailer lights not working
Hello everyone,
I've got a 1998 5.4L F150 with a towing package, 7 pin connector in the back. My open trailer has just a couple generic tail lights that aren't working.
I'm mechanically inclined and have a ton of tools, including a multimeter which I've used to check continuity and voltages coming out of the 7 pin connector, the 7-to-4 pin adapter I have, and even at the ends of the wires where the lights plug in. Looked at the bulbs, they seem to have no problems. Here's where I'm confused:
The 4 pin adapter shows LEDs for each of the 3 functions: LT, RT, and TM for left turn, right turn, and tail markers. The respective LED lights up when each of those functions are engaged inside the truck. Spiffy. Now, the 4 pin connector itself has a green wire coming from the RT, a yellow wire coming from the LT, a brown wire coming from the TM, and a white wire leading up to the 4th odd-ball pin...which I assume is a ground?
The problem is, using my multimeter, the only way I can get a voltage reading at the end of the wires (at the lights where I cut the wires to check voltage) while the right turn signal is engaged is with a configuration of the red lead attached to the green wire (RT) and the black lead attached to the brown wire (TM). I've traced the wires from the lights to the 4 pin connector and I don't see any obvious problems. I hooked up the red lead to the green (RT) and the black lead to the ground (white) and nothing happened.
Can anyone...enlighten...me? I gave up in frustration from what appeared to be an easy problem to fix...
I've got a 1998 5.4L F150 with a towing package, 7 pin connector in the back. My open trailer has just a couple generic tail lights that aren't working.
I'm mechanically inclined and have a ton of tools, including a multimeter which I've used to check continuity and voltages coming out of the 7 pin connector, the 7-to-4 pin adapter I have, and even at the ends of the wires where the lights plug in. Looked at the bulbs, they seem to have no problems. Here's where I'm confused:
The 4 pin adapter shows LEDs for each of the 3 functions: LT, RT, and TM for left turn, right turn, and tail markers. The respective LED lights up when each of those functions are engaged inside the truck. Spiffy. Now, the 4 pin connector itself has a green wire coming from the RT, a yellow wire coming from the LT, a brown wire coming from the TM, and a white wire leading up to the 4th odd-ball pin...which I assume is a ground?
The problem is, using my multimeter, the only way I can get a voltage reading at the end of the wires (at the lights where I cut the wires to check voltage) while the right turn signal is engaged is with a configuration of the red lead attached to the green wire (RT) and the black lead attached to the brown wire (TM). I've traced the wires from the lights to the 4 pin connector and I don't see any obvious problems. I hooked up the red lead to the green (RT) and the black lead to the ground (white) and nothing happened.
Can anyone...enlighten...me? I gave up in frustration from what appeared to be an easy problem to fix...
10-20-2014, 06:57 PM
#2
Senior Member
Make sure that white wire (grd) female pin is shorted to trailer frame. Taillights are grounded thru the frame of lights to trailer frame mostly. That white wire breaks off frame often.
When you check between green and brown you are getting a backcircuit ground thru wiring of truck so you may have missing ground.
I'd use meter ohm setting at X1. Put screw in each conn hole and using long spare wire measure from that to end of trailer wire at lights. Do that for green, brown and yellow. If good you have bad ground.
Its common for light bulb body to corrode in its socket.
From 40y elect teck who has trouble putting it into words, lol.
When you check between green and brown you are getting a backcircuit ground thru wiring of truck so you may have missing ground.
I'd use meter ohm setting at X1. Put screw in each conn hole and using long spare wire measure from that to end of trailer wire at lights. Do that for green, brown and yellow. If good you have bad ground.
Its common for light bulb body to corrode in its socket.
From 40y elect teck who has trouble putting it into words, lol.
10-20-2014, 07:21 PM
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I went back out and used jumper cables to attach the truck frame to the trailer frame and I managed to get voltage with the red lead on the green wire (RT) and the black lead on the trailer frame. Therefore I cut into the white wire at the 4 pin connector and tested continuity and yahtzee...infinite ohms. I replaced the white ground wire with some spare wire I had and managed to get the right turn signal working along with the tail lights, but then the LEFT turn signal wasn't working. I checked continuity in the yellow wire and had a fault there somewhere too. No more spare wire so I guess I'll just go buy a new 4 pin harness and hope for the best. I'll be back if that doesn't work! Thanks!
10-20-2014, 07:45 PM
#4
Senior Member
as stated, bad ground which you found.. the other possible problem for the left side...those 4 pin plugs will break wires at the plug.. all the use of plugging and unplugging... how many times do you grab the plug to unplug and just yank/pull the wires to unplug...lol...
10-21-2014, 10:33 AM
#6
Member
Troubleshooting Tricks
I put a new 7 Pin Connector on my '83 Camp Trailer yesterday. All is now well, and the intermittent LT Light now works. Lotsa Trailer Wiring is done with the smallest Gauge Wire that will get the job done. First thing I did on my Utility Trailer - where I could access the Wiring - was replace it all with Contractor-grade Extension Cord Wire.
1. Remove all Bulbs when Troubleshooting. Then, you don't have the path to Ground, or a deceptive path to other Wires, of a couple of Ohms.
2. I stick an ordinary Dress/Sewing Pin right through a Wire under test. I put a Clip Lead on one end of a Wire run near the Bulb, or at 'the other end' of whatever I'm trying to Troubleshoot.
3. This Clip Lead can be clipped onto one end of an unplugged Extension Cord. The other Extension Cord end can then be moved to the other end of the Wire/Circuit under test. A bent Paper Clip makes a handy 'Pin' to plug into a Female Extension Cord slot.
4. Note that Camp Trailer Running/Clearing Lights Wiring often goes into a sort of toothed compression bit piece of Metal, and back out to the next Running/Clearance Light. So, there can be a ~dozen Connections to become intermittent on that Lamp Circuit.
5. I use non-conductive 'Scotchbrite' Abrasive Cloth to shine and clean up various Connections. A little wad of it, held in the Jaws of Long Nose Pliers, is good for getting into tight spots - like Bulb Sockets - to ensure those 'Pads' are clean and conductive. I clean up every Connection/Lamp seasonally.
As dear ole Mom used to say: 'To assume makes an 'Azz' out of 'u' and 'me''. Assume nothing when Troubleshooting. Test every run of Wire, and every Connection. Then, move along to the next part. If you don't want to use +12 VDC from the Tow Vehicle when Troubleshooting, use a 9 VDC Battery + 2 Clip Leads [one side connected to Trailer/Chassis Ground]. Then, you can probe around to confirm there's 9 VDC on what you're testing once that 9 VDC is reliably connected to the Trailer-end Connector.
I repair using Solder and Heat Shrink Tubing. I don't like doing things over. I don't like Troubleshooting Road-side in the Rain.
1. Remove all Bulbs when Troubleshooting. Then, you don't have the path to Ground, or a deceptive path to other Wires, of a couple of Ohms.
2. I stick an ordinary Dress/Sewing Pin right through a Wire under test. I put a Clip Lead on one end of a Wire run near the Bulb, or at 'the other end' of whatever I'm trying to Troubleshoot.
3. This Clip Lead can be clipped onto one end of an unplugged Extension Cord. The other Extension Cord end can then be moved to the other end of the Wire/Circuit under test. A bent Paper Clip makes a handy 'Pin' to plug into a Female Extension Cord slot.
4. Note that Camp Trailer Running/Clearing Lights Wiring often goes into a sort of toothed compression bit piece of Metal, and back out to the next Running/Clearance Light. So, there can be a ~dozen Connections to become intermittent on that Lamp Circuit.
5. I use non-conductive 'Scotchbrite' Abrasive Cloth to shine and clean up various Connections. A little wad of it, held in the Jaws of Long Nose Pliers, is good for getting into tight spots - like Bulb Sockets - to ensure those 'Pads' are clean and conductive. I clean up every Connection/Lamp seasonally.
As dear ole Mom used to say: 'To assume makes an 'Azz' out of 'u' and 'me''. Assume nothing when Troubleshooting. Test every run of Wire, and every Connection. Then, move along to the next part. If you don't want to use +12 VDC from the Tow Vehicle when Troubleshooting, use a 9 VDC Battery + 2 Clip Leads [one side connected to Trailer/Chassis Ground]. Then, you can probe around to confirm there's 9 VDC on what you're testing once that 9 VDC is reliably connected to the Trailer-end Connector.
I repair using Solder and Heat Shrink Tubing. I don't like doing things over. I don't like Troubleshooting Road-side in the Rain.
