Low voltage for running lights

[elark7]

After spending time second guessing my ability to install a wiring harness on my trailer, redoing connections and grounds, I checked my Van. I am only getting 4-5 volts for the running lights- not a problem during the day but a big problem for night towing. The yellow marker lights midway back on the trailer come on but are dim, but the trailers main lights do not come on. I read about and checked the extra fuses my van has for trailer lights and they are good. All of my lights on the van work, the trailer has brake lights and turn signals but no running lights. Volt meter shows 4-5 at the van and the same at the lights? I hooked up my truck and running lights work fine. Am I missing a fuse somewhere or is the factory trailer harness bad somewhere. At $45 an hour (2 hour minimum charge) to trace the problem I would rather do this myself. I know I can just use the truck but the Van is my main long distance tow vehicle which is just about any lake I fish, plus it gets better gas milage and does not overheat while towing. Thanks.

E

 

[NYBo]

Re: Low voltage for running lights

I would suspect a corroded connection in the towing wiring harness. Does the harness use Scotchlok wire taps like these?

If so, this could be the problem.

 

[elark7]

Re: Low voltage for running lights

No, none of the quick connect tabs. It is a factory harness that has a round connector that plugs into the vehicle harness. It has to be the vans harness somewhere, since the lights work fine when hooked to my truck, but I can't find any loose connections (only has the one round plug) and the harness is completely enclosed in plastic. Another option, expensive, would be to order the vehicle side trailer harness. It is a 4 prong round plug only available from a dealer.

E

 

[bruceb58]

Re: Low voltage for running lights

Did you measure the voltage at the connector without the trailer lights hooked up?

 

[dingbat]

Re: Low voltage for running lights

I would check where the harness is grounded to the chassis. Run a seperate ground to the battery then check your voltage.

 

[Jchevy]

Re: Low voltage for running lights

Get on the backside of your connector on the van and check the brown wire for 12 volts, you can split the plastic the tape it back up when your done.

 

[elark7]

Re: Low voltage for running lights

Bruceb58- yes voltage at the plug, at rear of van, without the trailer hooked up is now 6.97 (up 1). Voltage at the vehicle plug (where the harness attaches mid way up the left frame) is 8.95. Dingbat-I tried to trace the harness to where the ground wire attaches but that was a dead end. The four wires inside the plastic go inside a metal tube next to the gas tank on the left frame rail. Where the wires exit under the drivers side it has already joined the main harness and is taped up very well. Jchevy- stuck a straight pin into the brown wire while it was attached to my meter and it is the same as the prongs on the front side of the plug. Dingbat-I am going to run a white wire from the back of the plug to a ground, maybe the auxillary battery on the right frame rail, to see what that does. Thanks again to you all for new insights.

E

 

[Jchevy]

Re: Low voltage for running lights

I don't think you have a ground problem you just don't have battery voltage. Problem is probley upstream on your wiring. See if you can find a fuse for the trailer runnig lights and check it there. If you get 12 high resistance is in the middle. What kind of van? I'll try to look at a wiring diagram.

 

[Splat]

Re: Low voltage for running lights

I don't think you have a ground problem you just don't have battery voltage. Problem is probley upstream on your wiring. See if you can find a fuse for the trailer runnig lights and check it there. If you get 12 high resistance is in the middle. What kind of van? I'll try to look at a wiring diagram.

However battery voltage is completed by both a positive and negative sides of the circuit. If ont fails the whole circuit looks bad. There is no half way here.

Personally I believe this will be a ground issue.

Bill

 

[dingbat]

Re: Low voltage for running lights

However battery voltage is completed by both a positive and negative sides of the circuit. If ont fails the whole circuit looks bad. There is no half way here.

Personally I believe this will be a ground issue.

Bill

Yep

 

[bruceb58]

Re: Low voltage for running lights

The easy way to see if its a ground is to have the negative meter lead with a long extension on it connected to your battery negative post and then probe the trailer connector.

 

[elark7]

Re: Low voltage for running lights

Ok. So after 5 hours of a torential downpour I gave up figuring this out yesterday. Today I ran a wire to the battery and have 8.32 volts for running lights, which is the same as what I get for the turn signals (there is 10.2 with brakes applied). I also grounded the plug to the bumper and got 8.2, while an exposed rusty area on the frame yeilded 6.2. What I don't understand is if the ground works all of the lights, why do only the running lights not work? I am going to drill and attach a ground wire to the frame, splice it in to the harness and then hook up the trailer to see what that does. Jchevy- It is a 2002 E350 Superduty 1 ton. I really need to get this fixed as I am suppose to tow the 30 foot band trailer to an away football game friday. Thanks again.

E

 

[Sea18Horse]

Re: Low voltage for running lights

The easy way to see if its a ground is to have the negative meter lead with a long extension on it connected to your battery negative post and then probe the trailer connector.

Bruce is right, this should be the first step in any trailer light diagnosis. If you still get the same readings then..........

The second step is to get an accurate wiring diagram for the vehicle in question. In the case of your van you would see that power to the park lights for your trailer plug comes from the "parking lamp trailer tow relay" located in your engine compartment battery junction block. In that same junction block there should also be "reversing lamp trailer tow relay". They should be the same style of relay. I would suggest that you swap these two and see what you get. If that doesn't help then you will need to check the power supply to that relay (again with your test light or multimeter grounded to the battery negative terminal with your long lead) and trace it from there. Good luck!

Cheers...................Todd

P/S, Power to the relay comes from fuse #14 in the battery junction block. A 30A fuse.

 

[elark7]

Re: Low voltage for running lights

Sea18horse- that was the first thing I did after going through the owners manual. Fuse was fine and I swaped C and D in the power distribution box. No change.

I connected a new ground wire from the frame to the plug and that did nothing. I ran a wire the length of the frame from the negative side of the battery to the plug and that got me very dim running lights, could only see them up close even when it got dark out. Showed 5.7 volts at the trailers lights. I decided to splice in at the wires for the taillights and bypass the factory harness but discovered that the harness for the taillights is not accessable from under my van. It appears that the wires run inside the van behind some of the plastic panals (no visable screws and the rear seat will have to come out as well). I guess I will have to take it to the shop and let someone else gouge me.

E

 

[Sea18Horse]

Re: Low voltage for running lights

I guess I will have to take it to the shop and let someone else gouge me.

...................well good luck with that.

 

[elark7]

Re: Low voltage for running lights

Just wanted to to let everyone know that I fixed this problem. I decided that if it wasn't the ground it had to be the positive side. Moved the wire to the positive terminal of the battery and put the other end in the trailer plug (trailer attached to the van). Lights worked. So I pulled the 30 amp fuse, still good, and checked for power coming through the fuse slots. With the lights on there was only 4-5 volts. So I pulled the relay, same here 4-5. Obviously there is a problem in the factory wiring and distribution system. So I ran a wire from the postive battery terminal to the fuse, pulled the lights on and bingo running lights on the trailer work. Checked the plug at the rear of my van with the lights off and there is no power, pulled the lights on and there is 11.95 at the plug. To be safe I ran an inline 20 amp fuse. Went to the High School and checked the trailer I am suppose to pull Friday night and all of the lights work fine. May not be the right way to fix this but it works and so far pulling the bass boat around in the dark has not blown any fuses. So no gouging by the local "experts". Thanks again for all the help.

E

 

[Knightgang]

Re: Low voltage for running lights

99.9% of all trailer light issues turns out to be a Bad Ground. Your issue fell into the 0.1% that most people never think about...

Great job and I am glad you found the problem.

I had a similar issue with power door locks once in a 95 Suburban. They worked with the Key Ring FOB, but not at the door button on either door. Was not getting 12vDC to the switch. Pulled a wire hot with 12vDC and bingo, both door lock buttons worked. Never had another issue with them...