# Trailer brake lights but no running lights.



## fishngolf (Jul 18, 2009)

I turn on my lights in truck but no lights on on trailer limiting me to only travel during the day.. Brake lights work on trailer though. Any good thoughts on where I should start lookingfor the problem?
Light bulbs?
Harness plug(s)
Harness?

Thanks


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## Cajunsaugeye (Apr 9, 2013)

Bad ground 90% of the time.


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## sherman51 (Apr 12, 2011)

I would start looking at a corroded plug. have someone watch the lights while you wiggle the plug and see if the lights flicker. take a 12v tester and see if your getting juice to the plug from your truck. you may also have a bad wire on your trailer going to the tail lights. check your ground wires. these are some problems I've run into over the yrs.
sherman


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## FAB (May 26, 2013)

fishngolf said:


> I turn on my lights in truck but no lights on on trailer limiting me to only travel during the day.. Brake lights work on trailer though. Any good thoughts on where I should start lookingfor the problem?
> Light bulbs?
> Harness plug(s)
> Harness?
> ...


If you have a later model GM product check the fuse box there are separate fuses for the turn signals brake and tail lights going to the trailer connection.


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## ddcollier (Feb 13, 2011)

are you leaving ur headlight switch on auto? turn the switch to manual on, then try ur trailer lights. i think some factory trailer lights are wired to only send juice to the plug when turned to manual on?


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## fishngolf (Jul 18, 2009)

Ok thanks Sherman and FAB. I will start with the wiggle idea and a 12v tester on plugs.


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## fishngolf (Jul 18, 2009)

ddcollier said:


> are you leaving ur headlight switch on auto? turn the switch to manual on, then try ur trailer lights. i think some factory trailer lights are wired to only send juice to the plug when turned to manual on?


I get brake lights ok on trailer no running lights.


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## waterfox (Dec 27, 2014)

fishngolf said:


> I get brake lights ok on trailer no running lights.


check at plug on truck for 12 v
plug in trailer and with a hat pin or needle pierce wire about 2 inches back..
on 4 wire system it should be brown
remove lens carefully check inside socket for 12 v
if frame is not grounded use a piece of wire from batt to
meter for ground.
if they never worked some new trucks have all kinds of fuse
and relays
good luck


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## bountyhunter (Apr 28, 2004)

my 2005 ford f150 has a separate fuse for running lights, ITS #10 on the passenger side fuse panel took me an hour to figure this one out ,everything worked,, no running lights.


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## fishngolf (Jul 18, 2009)

Thanks! I have a 2002 ford escape. I will be sure to check that one out tomorrow.


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## brent k (Nov 10, 2013)

Please do not pierce the wire insulation. It will corrode and cause you more headaches in future.
Start at the connector for tow vehicle. 
Take a test light and clip lead to ground which will be the pin that sticks out of connector.
Now take probe of testlight and probe the port for the brown wire. If your test light aluminates then this tells you you have 12v and ground at your connector for the tow vehicle and that the issue is in the trailer. Pm me and i will give you my phone number and help guide you threw this to isolate the issue.


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## waterfox (Dec 27, 2014)

brent k said:


> Please do not pierce the wire insulation. It will corrode and cause you more headaches in future.
> Start at the connector for tow vehicle.
> Take a test light and clip lead to ground which will be the pin that sticks out of connector.
> Now take probe of testlight and probe the port for the brown wire. If your test light aluminates then this tells you you have 12v and ground at your connector for the tow vehicle and that the issue is in the trailer. Pm me and i will give you my phone number and help guide you threw this to isolate the issue.


have been piercing wires on all kinds of trailers for more than 50 years and never had a problem. the needle makes a very small hole 
also i solder connections instead of wire nuts.


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## brent k (Nov 10, 2013)

waterfox said:


> have been piercing wires on all kinds of trailers for more than 50 years and never had a problem. the needle makes a very small hole
> also i solder connections instead of wire nuts.


Not gonna argue with it as it is sensless. All i will say is im a professional mechanic by trade. I work for a large semi truck and trailer repair and towing company. I have years of experiance. I can take pictures and show proof of what punctured wire insulation results are. My speciality in my trade is electrical. I guess maybe the reason i repair so many wire harness on a daily/weekly basis is because you have been puncturing wires with a test light probe for years. Thank you for keeping me employed sir and paying for my home and boat ect ect. Oh and by the way keep on a keepin on what your doing so i keep getting work.


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## EB1221 (May 24, 2012)

I'm going to be real silly here....did you replace the bulb ? also check the socket for corrosion. otherwise all above is good info.
EB


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## fastwater (Apr 1, 2014)

As *brent k* stated, piercing the insulation on wiring is never a good idea. Piercing the insulation is a sure fire way of letting moisture into the wiring causing corrosion and future problems. Especially with application in damp inviroments such as a boat trailer that gets put in water. 
Check for current at the start of a circuit with a tester/test light. Then follow those wires to where the next connection is at. If you have current from the start of the circuit as well as in the first connection you come to, then all is well in that section of wiring. Then carry on from that last connection to the next taking your testing process a step at a time. If you have current at the start of a connection and nothing where the next connection is at with nothing but wiring in between, then 9 times out of 10 there's a broke/corroded wire in that section of wiring. A continuity tester well tell ya for sure about broken wiring inside a length of wiring. 

I'm thinking since your trailer brake lights are working that most likely your ground is good. Same ground that is needed for the brake lights is also the ground for the running/ts lights. IMO, from the sound of things(if your trailer lighting fixtures and bulbs are good) you have a current/power issue. 

FWIW, agree that most lighting issue's on trailers are caused by bad ground. You can cut these issue's down drastically by not only wiring the ground into the standard ground wiring coming back from the plug as normal but grounding each light fixture separately to the trailer at the fixture as well.


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## brent k (Nov 10, 2013)

fastwater said:


> As *brent k* stated, piercing the insulation on wiring is never a good idea. Piercing the insulation is a sure fire way of letting moisture into the wiring causing corrosion and future problems. Especially with application in damp inviroments such as a boat trailer that gets put in water.
> Check for current at the start of a circuit with a tester/test light. Then follow those wires to where the next connection is at. If you have current from the start of the circuit as well as in the first connection you come to, then all is well in that section of wiring. Then carry on from that last connection to the next taking your testing process a step at a time. If you have current at the start of a connection and nothing where the next connection is at with nothing but wiring in between, then 9 times out of 10 there's a broke/corroded wire in that section of wiring. A continuity tester well tell ya for sure about broken wiring inside a length of wiring.
> 
> I'm thinking since your trailer brake lights are working that most likely your ground is good. Same ground that is needed for the brake lights is also the ground for the running/ts lights. IMO, from the sound of things(if your trailer lighting fixtures and bulbs are good) you have a current/power issue.
> ...


Also speaking of ground issues...one thing i do is go to any automotive parts store buy two medium sized gator clips and take a 18-24" section of 12-14 gauge wire. Strip each end of the wire and attach gator clips. Now you have a dedacated ground lead. Take a piece of emory cloth or even sand paper and buff a small inconspicuous spot on both your reese frame mount and a small area on tongue of trailer and attach gater clip to trailer and tow vehicle. Ground issue solved. 

I made a few of these and keep one on boat trailer one in tow vehicle and have a spare. Having this little lead means rest assured i always have geound and it is one way to eliminate any ground issues. And ensure good turn indicators instead of turn indicators causing all the lights to try and blink.


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## fastwater (Apr 1, 2014)

...and if you don't have these jumper wires made up but have a pair of regular battery jumper cables handy you can do the same thing for testing purposes with those. Just make sure and attach same color cable end to tow vehicle and boat trailer


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## c. j. stone (Sep 24, 2006)

sherman51 said:


> I would start looking at a corroded plug. have someone watch the lights while you wiggle the plug and see if the lights flicker. take a 12v tester and see if your getting juice to the plug from your truck. you may also have a bad wire on your trailer going to the tail lights. check your ground wires. these are some problems I've run into over the yrs.
> sherman


Running lights are the brown wire. There's an inexpensive plugin that lights up to tell you if the truck's wiring is good. You'd have to check the trailer(brown wire) all the way back to the lights. Be sure to check the ground wire(like someone posted, bad grounding is 90% of trailer wiring problems!) Change the bulbs and spray some conducting lubricant into the sockets. An interim, quick fix is to go to Harbor Frt and get the "magnetic" trailer light kit($10)! Looks like crap with all the exposed wiring, but works great, and you will get many other uses out of it.


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## lostinthefifties (May 26, 2014)

fishngolf said:


> I turn on my lights in truck but no lights on on trailer limiting me to only travel during the day.. Brake lights work on trailer though. Any good thoughts on where I should start lookingfor the problem?
> Light bulbs?
> Harness plug(s)
> Harness?
> ...



Has that problem with my horse trailer and boat trailer too. It "should" be in the plug from your trailer. 1) You need a 12V tester.
Checking each din on the plug from vehicle and coinciding them with your trailer plug. Should be simple. Let me know. I'm in Powell if you needed help.


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## Shortdrift (Apr 5, 2004)

fishngolf said:


> I turn on my lights in truck but no lights on on trailer limiting me to only travel during the day.. Brake lights work on trailer though. Any good thoughts on where I should start lookingfor the problem?
> Light bulbs?
> Harness plug(s)
> Harness?
> ...


Well. After all the advice, did you get it fixed?


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## lostinthefifties (May 26, 2014)

Great one Shortdrift. Sooooooo?????? Fixed or not, and how did you do it?


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## sherman51 (Apr 12, 2011)

just fixed the same problem on a new chevy truck. its the fuse out under the hood. the running lights for the trailer works off its own fuse. I forget which fuse it was but the lid on the fuse box will tell you which fuse is for your trailer running lights.
sherman


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## fastwater (Apr 1, 2014)

Doesn't it just get your shorts in a wad when guys ask questions and people are willing to try to help, then they give no response? At least they could come back with a report. Especially if they fixed their problem so others could learn as well.


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## BuckeyeBassMan (Jun 8, 2004)

I had the same question posted in the trailer section. Running lights were the fuse. You guys were a big help on that one, still working on a turn signal though


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## fastwater (Apr 1, 2014)

Thought your brake lts. and T-sig lts.(blinkers) were working okay.

Whats going on with your TS's (I.E. neither side working, working intermittently,etc) ? 

Understand you found a fuse in the truck blown that is dedicated to your trailer lights. Were you having trailer *TS* issue's before that fuse blew? The reason I ask is *that fuse blew for a reason*. 

Check your bulbs out well. Sometimes the small filament inside of a bulb that operates the TS-brake side of the bulb will blow and that small wire inside the bulb will lay down on the filament operating the running lights causing lights not to work properly or even fuses to blow.

Really check your trailer grounds and connections out well (wire not broke, grounding points not rusty corroded, bulb sockets not corroded, grounds inside of light fixture themselves are good). Start at where your trailer wiring is tapped into the trailer plug wiring and work back. 

Also, FWIW, have found that running an additional ground wire from the ground of each trailer light to the trailer frame itself sure helps in a lot of ground issues.


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## papaperch (Apr 12, 2004)

http://www.etrailer.com/dept-pg-Wir...Testers.aspx?gclid=CO_-6c6f9cYCFcERHwodoRIIVQ

Anyone that want to trouble shoot their own trailer lights should own one of these. It will tell you instantly if it is the towing vehicle or the trailer.

Guys will often spend hours trying to trouble shoot the tow vehicle's wiring all the while it is in the trailer wiring. Or vice versa one of my friends replaced the entire wire bundles on his trailer. Finally called me for help after blowing a lot of his time. His problem was in the vehicles pig tail wiring. One of the clamp down connectors wasn't seated all the way and had lost contact. Squeezed connector with pliers to re-seat and he was good to go.

Even though I have a multimeter I still use this first to isolate the problem. 12 volt wiring systems are very simple. But their simplicity makes them a bug-a-bear to troubleshoot. Most people usually overthink the problem. 12 volts DC circuits are not capable of producing mysterious one of a kind never before seen problems. Despite my relatives and friends protests to the contrary.


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