Trailer lights acting funny

99% odds it's a grounding problem. :thumbup:

Yeah, figured that one all on my own. I just don't know how to troubleshoot it to find where the fault is. Thoughts?

Some trailers are grounded thru the vehicle hitch, so you can try wirebrushing the hitch ball first.

If that doesn't work, check for a loose white wire @ the trailer tongue or at the left rear tailight.

If that doesn't work, check the white wire at each taillight & running light.

If all of that doesn't work, check all the wires to make sure they didn't wear thru, especially at penetrations.

Post a schematic; we'll step you through it.
You can use clip leads and the vehicle battery to check the trailer lights separately from the vehicle.

This lamp or equivalent used?

#1034 MINIATURE BULB BAY15D BASE - 12.8/14.0 Volt 1.80/0.59 Amps S8 Double Contact (DC) Index Bayonet (BAY15d) Base 200/5000 Average Rated Hours 2.00" Maximum Overall Length #1034

A bad ground will cause the thick filament to supply current to the thin filament, but the thick one doesn't light while it's doing this.

I'll put something up - just for giggles it appears that they coated all the wires black with some sort of paint.

If the bulbs are 1157 type Check the bulbs for corrosion at the terminals.. I replaced the lights on all my trailers with the LED style... Now I have o light problems

Is this problem specific only to this trailer? The first check would be on the tow vehicle. You can purchase a test light that plugs into your trailer light connection for only a few dollars. Most problems I have had with trailer lights either is a ground on the tow vehicle or problems in the connector itself.

Reality check - I'm used to house electrical so 12V DC is a strange new world. There are only two wires that run to each light. One is 'hot', right? The other is the 'ground/neutral'? If I run another 'white neutral' do I use it in lieu of the ground/neutral? In addition?

The wires running into the lights are both the same colored wire.

Leah Frances said:

Reality check - I'm used to house electrical so 12V DC is a strange new world. There are only two wires that run to each light. One is 'hot', right? The other is the 'ground/neutral'? If I run another 'white neutral' do I use it in lieu of the ground/neutral? In addition?

The wires running into the lights are both the same colored wire.

Click to expand...

Nothing like residential wiring. If I remember correctly:

White = ground
Brown = tailights/running lights
Yellow = left turn
Green = right turn

So, you should have a brown & yellow going to left tail, & brown & green going to right tail, theoreticaly. I would take a closer look at the left tailight , as it has to be grounded through the frame some how. I'm sure it too rusty/corroded to make a good ground.

Connection (ground) is established through the bolt that fastens the light to the trailer. I will check to make sure the connection is good and free of corrosion. FYI, the trailer is less than 1 year old.

Nobody ever died from 12v in the conventional sense so Hot and Neutral kind of lose their meaning, along with the wire colors.

Each side light has two wires going to it. White wire seems to terminate at the ball. If I want to run a separate neutral/ground what would I hook it up to at the light end. Each light has two terminals - where would I attach the white?

If you have the 4 prong plug .The w from the plug will have to tie into both whites at the lights that wat you are directly grounded to the lights.. Not grounding through the trailer frame

Leah Frances said:

Each side light has two wires going to it. White wire seems to terminate at the ball. If I want to run a separate neutral/ground what would I hook it up to at the light end. Each light has two terminals - where would I attach the white?

Click to expand...

The ground connection is the lamp housing. I'd put a ring terminal on your new ground wire and put the terminal between the head of the bolt and the housing.

Added: Automotive (trailer) wiring is suspect to corrosion. Get the shrink style ring terminals.

Looks like there are several wiring methods out there
http://images.google.com/imgres?img...m&hl=en&safe=off&client=safari&rls=en-us&um=1

Cool. I've got a spare spool of brown bell wire I can use to do the neutral/ground.

Just kidding. :laughing: White wire it is!