trailer wiring

[Cruiser]

I've spent all day trying to reconnect wires and nothing works! A mechanic got the lights working when we brought the trailer home. Now after new floor and insulation are in, I'm installing new wiring. I marked the hodge-podge of old wires to reconnect as before, but without success.

I looked at the wiring diagrams off MarksRV website and found that the GM wiring code seems to match what's on the tow vehicle: white-ground; yellow-left/brake; green-right/brake; brown-running/tail lights. I tried variations of these in the trailer, but no luck.

Two things confuse me about the existing connection.
1) The brown wire from the car is connected to two wires in the trailer, one for running/tail lights and one for brakes. The brake and tail lights appear to be wired to the same bulb. The turn signals each have a dedicated wire and bulb. This is different than the car where turn signals and brakes appear to be wired together and running lights are separate.
2) From the car, in addition to the flat 4-wire, there's also a sheathed cable w/ 10ga black and white wires (from the brake controller?). The white wire together with the white ground of the 4-wire are connected to the two trailer brake wires. Does a ground exist for lights if the white 4-wire is going to the trailer brakes? The black wire isn't connected at all. We were told a wire was installed to connect later to charge the battery, so I assume this is that wire?

Is there a procedure for connecting trailer wires, or is it by trial and error? Does it work to try one or two connections before connecting all the wires, or does the entire system need to be in place first?

I hope that this makes sense to someone who can give some advice or direct me to resources. Boy, I'd tow the trailer to the RV store tomorrow if I could move it. Trying to figure this out is the hardest part yet of restoring this old trailer.

Doug

[Fun-Lovin]

I ran into similar problems when working with my dads a/s.
When testing everything on the trailer worked, but when I hooked to his truck directly nothing worked. His problem turned out to be the plug on the trailer and the cable to the truck didn't want to work together well. It was just sure age and use of the original socket and plug. I replaced both with the new rv style 7 round plug and socket and it all worked perfectly.
Normally the brake and turn lights are the same, the tail lights are combined on both sides.
Here is a suggestion for you to run down and find out exactly what you have and what pins go to what lights. Use a circuit tester (its a light in a probe with a wire and a gator clamp). Use this to find the correct wire on the tow vehicle if you don't already know what they are. Clamp the gator clip to a good ground on the tow vehicle, test each circuit (l,r turns and tail lights, power wire). Once you know and label these your ready to get started. I built a set of jumper wires to test the trailer lights using 16 guage wire and gator clips. Clip one wire to a good ground on both tow vehicle and trailer, connect power wire on tow vehicle to other jumper clip (you may want a fuse in this wire but not a big one 5 amps) one at a time check the wires to the trailer wiring harness. this will tell you what connection on the trailer goes to what. This is trial and error but works. If you blow the fuse you may have hit the ground.

[bryanl]

Iff you use a light bulb as a test indicator, you should not have to worry about blowing any fuses.

On the tow vehicle, run the lightbulb as suggested with one lead attached to the vehicle ground. Activate each circuit one at a time and see which pin causes your bulb to light to identify the pin connections on the tow vehicle.

On the trailer, connect one end of the light bulb tester to +12. Connect the other to each trailer pin one at a time and see what lights up. In most cases, you'll get a dim light as the indicator bulb and the trailer circuit are in series (protects fuses) but you should still be able to see which trailer circuit is connected to what pin. You can check for brakes by getting a wheel off the ground and spinning it to test if the brake is activated. If you can't see the bulb light the first time around, then you can try +12 to that pin to brighten things up a bit (but this hazards fuses).

Standard wiring goes somewhat like this

1- white - ground
2-brown - right turn/brake
3-green - running lights
4-red - left turn/brake
5-yellow - brakes
6-black - backup lights
7-blue - battery

The color code seems to be rather well followed.

[Cruiser]

Yes, a circuit tester is what I need. I've printed out your replies and will try to tackle this again next weekend. Thanks for the advice. Right now I'm going to install my new fenders and finish bolting down the new floor - something to build up my confidence before trying the wiring again! I'll let you know how it goes this weekend.
Doug

[Fun-Lovin]

I only wish I had to work on something easy like the wiring last weekend. Im sore in places that I didn't think I had muscles.
Installed a frame stiffening kit oh yea.