Newbie help...horse trailer/brake connector/fuse problem

[pasturepony]

Good afternoon everyone!

I have a number of issues stemming from one problem so please bare with me! lol

I have a 99 Dodge Diesel 4x4 2500 and a two horse Bison bumper pull trailer.

For starters, I bought a used horse trailer a few months ago and during state inspection it failed because the trailer brake lights and turn signal on the right side did not work. I took it home, played with it, replaced the brake/turn signal light assembly and carriage, checked fuses, etc. No luck. Then I wiggled the wire connector/plug from trailer to truck and got the turn signal to work but not the brake light.

So Friday I replaced the plug on the trailer side. One problem was the trailer plug is a 5 wire plug but the truck is a standard 7 wire RV plug. So I replaced both the 5 wire plug and the 7 wire adapter. I wrote down the color scheme and letters and replaced it exactly. No luck. Oh, and I used two trucks to check the issue in case the issue was in the truck. Same on both trucks...

Next I pulled the light assembly out again to find that the white wires had come undone at some point. I reconnected them and Wahla! The brake lights worked!

Thinking all was fine and dandy I hooked the truck up and went to haul the trailer. When I got in the truck I noticed that the brake connector box's green light in the truck was not on which is not good. The green light is always on even when no trailer is attached. I figured I blew a fuse. When I tried pulling the trailer the trailer brakes locked up and wouldn't unlock.

Frustrated, I left it overnight. This morning the battery was dead on the truck...charging now...someone explained this is because the trailer breaks being locked drew power from the truck. Not sure if that is accurate.

So today I checked all of the fuses but not the relays. I checked both the box inside the cab and the one near the engine. I did not see any problems. The brake box light still will not go on.

Any ideas on where to start with the fuse/brake box issue? Ideas on which wires I probably have crossed on the trailer plug? Ideas in general? I'd really appreciate any help!

Thanks!!!!!
-Korinne

[BernieB]

Obviously the trailer wiring and the truck wiring have some differences, so let's begin by looking at what is actually correct for each terminal. You'll probably find this link helpful:
Trailer Wiring Diagrams

[BernieB]

Starting from that you should be able to check the trailer wiring and make sure each connection is correct. I suspect that what you are going to find is that pin #4 of your 7 pin connector is being sent to the electric brake controller on the trailer. Possibly the adapter you're using is no good, or incorrect for this application or, equally possible, whoever had the trailer before you didn't wire it using standard pin connections, and just hooked it up using any old pin combination and matched it on their truck.

I think your best solution might be to just rewire the trailer completely, using a compatible 7 pin connector and harness. Any un-needed wires (like backup lights) can simply be capped off on the trailer.

[pasturepony]

That was a great link!! I originally bought a 7 pin plug rather than the adapter but when I opened up the 5 pin I had no idea where to put the 5 wires in the 7 or 8 spots (my trailer doesn't have the 6th wire for the 12v) so I didn't know which ones to leave empty. I'll go pick up the 7 plug again as I returned it.

Thanks!

I'll get back to you all later this week as I'll have to do this after work this week....need to get back on the tractor tonight before the light fades!

Most likely I'll be back with a lot more questions! Any ideas on how to find that fuse so I can pick up an extra couple of fuses? I see people talking about cavity number X but can't find any diagrams which have numbers for the cavities in the fuse boxes on the dodge ram.

Thanks again!!

[BernieB]

Originally Posted by pasturepony

That was a great link!! I originally bought a 7 pin plug rather than the adapter but when I opened up the 5 pin I had no idea where to put the 5 wires in the 7 or 8 spots (my trailer doesn't have the 6th wire for the 12v) so I didn't know which ones to leave empty. I'll go pick up the 7 plug again as I returned it.

Thanks!

I'll get back to you all later this week as I'll have to do this after work this week....need to get back on the tractor tonight before the light fades!

Most likely I'll be back with a lot more questions! Any ideas on how to find that fuse so I can pick up an extra couple of fuses? I see people talking about cavity number X but can't find any diagrams which have numbers for the cavities in the fuse boxes on the dodge ram.

Thanks again!!

Glad the link helped you out.

As to what fuse is what, usually the number is molded in the plastic on the fuseblock, and the chart is on the inside of the fuse door.

BTW, where in Northern VA are you? I live in Fredericksburg, but might be taking a ride up to the Sterling/Leesburg area next weekend to make a delivery. I could maybe stop by and lend a hand if you don't have it working by then.

[BernieB]

One more little bit of advice for you... A good, solid ground between the trailer and the towing vehicle is the single most critical aspect of getting trailer lights working. I've found that connecting the white wire (ground) on the trailer harness to a firmly attached lug on the trailer, using a "star" washer, helps quite a bit. I also use a simple test light to check grounds on lights. The way it works, I attach the clip on the test light to a good ground on the trailer, then use the point to probe the ground (never the 12v side) on the faulty light itself. If the light is properly grounded then nothing will happen, but if the ground on the light is bad then the current will try to flow to ground through the test light, making it light up (though it can be very dim if it's a partial ground). Or, just use a piece of wire with an alligator clip on one end. Clip it to a good ground on the trailer and probe the ground side of the light (never the "hot" side!) and if the light gets brighter or starts working then you know the ground isn't any good.

Of course, all this depends on having a good ground between the tow vehicle and the trailer to start with, and for that a regular pair of jumper cables can help. Hook one black clip to the frame of the tow vehicle and the other to the frame of the trailer. If all your light problems are suddenly "solved" then you need a better ground connection between the tow vehicle and the trailer.

(It gets easier the more times you've fixed problems like this, and I've towed everything from flatbeds to boats)

[leolkfrm]

when you wire the plug make sure your reference point is correct for the end you are wiring