Anyone know the skinny on trailer lights?
09-20-2006, 05:56 PM
#1
Safety Car
Thread Starter
Anyone know the skinny on trailer lights?
(Mods - not sure where to put this, seems like there might be more guys who trailer their cars here than in the tech forums but move if necesary)
Can anyone tell me (or check) if you need to have a solid ground to get turn signals and brake lights? I have running lights but turn signals and brake lights aren't working. The trailer is fine (I tried it with another vehicle) so it has to be my truck.
I checked voltage and resistance at all 7 pins and the only thing I can't seem to get is a perfect ground at that pin. Could that explain why the signals aren't working?
TIA
Can anyone tell me (or check) if you need to have a solid ground to get turn signals and brake lights? I have running lights but turn signals and brake lights aren't working. The trailer is fine (I tried it with another vehicle) so it has to be my truck.
I checked voltage and resistance at all 7 pins and the only thing I can't seem to get is a perfect ground at that pin. Could that explain why the signals aren't working?
TIA
09-20-2006, 08:46 PM
#2
Team Owner
Member Since: Apr 2002
Location: Zionsville, PA NRA Life Member
Posts: 25,778
Likes: 0
Received 0 Likes
on
0 Posts
St. Jude '03-'04-'05-'06-'07-'08-'09-'10
Since the trailer lights work correctly on another vehicle, it seems to be the ground on your truck. If you don't have a good ground you can NOT complete the circuit.
Take a piece of wire and ground it to the frame of the truck and to a good ground on the trailer. If your lights work correctly then replace the ground wire on your plug. If the plug corroded, it might be a good time to just replace it.
( I feel like I'm telling you something you already know)
Jeff
Take a piece of wire and ground it to the frame of the truck and to a good ground on the trailer. If your lights work correctly then replace the ground wire on your plug. If the plug corroded, it might be a good time to just replace it.
( I feel like I'm telling you something you already know)
Jeff
09-20-2006, 09:24 PM
#4
Team Owner
If your clearance lights are working, then you should have some semblance of a ground connection from the truck to the trailer. The fact that all the trailer light work when powered from another vehicle points to a problem on your trucks connector.
Do you get 12v at the brake light terminal on the truck harness when the brake pedal is depressed? Is there 12v at the tail lamp connector? Does a test light flash at the brake light terminal when the turn signals are turned on?
Test the connectors using both a separate good ground and the ground pin on the connector. If a jumper wire between the truck and the trailer gets the trailer lighst working properly, then I would check the truck connector ground wire and the connector.
It's probably worth replacing the truck connector if the current one shows signs of age (like the wire coverings are brittle or have cracks) or the connectors have corrosion on them.
Do you get 12v at the brake light terminal on the truck harness when the brake pedal is depressed? Is there 12v at the tail lamp connector? Does a test light flash at the brake light terminal when the turn signals are turned on?
Test the connectors using both a separate good ground and the ground pin on the connector. If a jumper wire between the truck and the trailer gets the trailer lighst working properly, then I would check the truck connector ground wire and the connector.
It's probably worth replacing the truck connector if the current one shows signs of age (like the wire coverings are brittle or have cracks) or the connectors have corrosion on them.
09-20-2006, 10:29 PM
#5
Cartoon Character
Member Since: Jun 2006
Location: Can't be more than 114... Arizona
Posts: 1,440
Likes: 0
Received 0 Likes
on
0 Posts
You do not need the ground pin for the signals or anything else unless you have a rubber ball on your hitch,, The hitch ball is attached to the truck frame which is ground as are the lights on commercial trailers connected to the trailer frame for grounding. ( I know, I manufacture race trailers as a side business). Is your truck american made, ie same light for signal and brake? If so then you need to check the fuses for the brake lights or select one of the turn signals, say left and stick your meter in the pin for left and ground it to the bumper. You should see a voltage change. If you don't, it's a fuse or a broken wire...
Steve
Steve
09-21-2006, 02:40 PM
#6
Safety Car
Thread Starter
This is getting strange. As a precaution I replaced the plug on the truck (it's a 2005 Jeep Grand Cherokee, BTW) and re-did the ground wire.
At each pin I have exactly the signal I should have (and same as on the other vehicle I used to check the trailer).
Running lights - 12V when tow vehicle lights are on
Turn signals - fluctionating between 12 and 0 as the light flashes
Brakes - constant 12V when pedal depressed
GND - uh...0 V
Plus I checked the resistance between the ground pin and the vehicle body and the it was in the 5 Ohm range...this indicates a common ground to me.
As for the ball of the hitch acting as a surrogate ground, this occurred to me as well, but when I tried the other vehicle all I did was back it up close and plug in the harness, I didn't actually hook it up. Therefore nothing was creating a ground between the two.
Anyway, after the connector replacement and the ground fix I have the exact same problem. I'm running out of ideas.
At each pin I have exactly the signal I should have (and same as on the other vehicle I used to check the trailer).
Running lights - 12V when tow vehicle lights are on
Turn signals - fluctionating between 12 and 0 as the light flashes
Brakes - constant 12V when pedal depressed
GND - uh...0 V
Plus I checked the resistance between the ground pin and the vehicle body and the it was in the 5 Ohm range...this indicates a common ground to me.As for the ball of the hitch acting as a surrogate ground, this occurred to me as well, but when I tried the other vehicle all I did was back it up close and plug in the harness, I didn't actually hook it up. Therefore nothing was creating a ground between the two.
Anyway, after the connector replacement and the ground fix I have the exact same problem. I'm running out of ideas.
09-21-2006, 03:08 PM
#7
Burning Brakes
Chase it down!
If you have the 12 volts coming on at the connector you need to chase it down the harness. Connect the trailer to the truck and use the "half method" of troubleshooting. Go to the lights and see if you have voltage at the fixtures. If you do, work on the fixtures. If you don't move to about half way between the fixture and the trailer connector. Use a safety pin and press it into the turn signal wires to see if you have voltage. If you do, move back half way towards the fixture and try this test again. If you don't have voltage move forward towards the connector and do this test again. You get the idea.
If you are getting some light then it would appear you have ground. The brake and turn signal lights are the same filament in the bulbs so make sure you simply don't have two defective bulbs.
Good luck,
If you are getting some light then it would appear you have ground. The brake and turn signal lights are the same filament in the bulbs so make sure you simply don't have two defective bulbs.
Good luck,
09-21-2006, 04:20 PM
#8
Drifting
Q: You actually plugged this trailer into a plug on another two vehicle and all works fine?
If yes then does you plug on the jeep match that plug?
Are we correct in assuming that you have tail lights ... not just running lights on the trailer some place else? Tail lights in the fixtures that are to blink?
OK then:
Hook the bugger up and turn the lights on and a turn signal. Go to the tail light and check voltage. If 0 then broken wire along the way. I would then get a pin and check the wire on the trailer side right at the connector to see if you have voltage right there. You already verified voltage on the Jeep side - right? Likely the problem is here since the trailer works otherwise. Jeep side not getting to the trailer side.
You do need ground for brake/turn. No ground = no light
Mine is hard grounded at the tail light and has two hot wires. One is for tail and the other for turn/brake. The tail light wire is common to both sides.
What type of plug is on your Jeep? It only requires 4 wires unless you have brakes then you need the round RV plug but there are two flavors of those and they wire different. One uses pins and one uses flats.
Here is a link too. Jeep seems different than most as to colors.
http://www.etrailer.com/faq/wiring.asp
L - T&B
R - T&B
Tail
Gnd
If yes then does you plug on the jeep match that plug?
Are we correct in assuming that you have tail lights ... not just running lights on the trailer some place else? Tail lights in the fixtures that are to blink?
OK then:
Hook the bugger up and turn the lights on and a turn signal. Go to the tail light and check voltage. If 0 then broken wire along the way. I would then get a pin and check the wire on the trailer side right at the connector to see if you have voltage right there. You already verified voltage on the Jeep side - right? Likely the problem is here since the trailer works otherwise. Jeep side not getting to the trailer side.
You do need ground for brake/turn. No ground = no light
Mine is hard grounded at the tail light and has two hot wires. One is for tail and the other for turn/brake. The tail light wire is common to both sides.
What type of plug is on your Jeep? It only requires 4 wires unless you have brakes then you need the round RV plug but there are two flavors of those and they wire different. One uses pins and one uses flats.
Here is a link too. Jeep seems different than most as to colors.
http://www.etrailer.com/faq/wiring.asp
L - T&B
R - T&B
Tail
Gnd
Last edited by rbl; 09-21-2006 at 04:26 PM.
09-21-2006, 05:23 PM
#9
Cartoon Character
Member Since: Jun 2006
Location: Can't be more than 114... Arizona
Posts: 1,440
Likes: 0
Received 0 Likes
on
0 Posts
AHH
Perhaps as you did not hook up the trailer to the other car your ground and hot wires are reversed on the stop lights and signals? This would send the 12v to ground and nothing would happen. I have also seen weird stuff when the lamps are in backwards... or the sockets could be wired backwards? Try not hooking the trailer to your vehicle and see if it works. Then I would shut off the car if it works and check the resistance between the bumper and the brake/signal wires on the tow car. If it is 0 ohms then you will have found the fault.
Steve
Perhaps as you did not hook up the trailer to the other car your ground and hot wires are reversed on the stop lights and signals? This would send the 12v to ground and nothing would happen. I have also seen weird stuff when the lamps are in backwards... or the sockets could be wired backwards? Try not hooking the trailer to your vehicle and see if it works. Then I would shut off the car if it works and check the resistance between the bumper and the brake/signal wires on the tow car. If it is 0 ohms then you will have found the fault.
Steve
