Shopsmith Forums

for connecting the wires between a tow vehicle (truck) and the towed vehicle (trailer).

The connector on my Ford is different than the connector on the truck that is going to be used to tow the trailer to my house. The connector on the trailer (to be towed) looks like the connector on the truck that is going to be used to tow the trailer but when connected to that truck the running lights, brakes lights and directionals do not work properly.

I can sift through this and connect the trailer to the truck just to make it work but I would rather do it so that any truck could be used. Is there a standard interface definition for this.

I already know, from looking at three different commercially prepared cables, that there is no standard color code. That would make it all too easy.

Try this sight. Has all the standards for 4-7 pin styles along with wiring color codes for some types of vehicles.

http://www.etrailer.com/faq-wiring.aspx

There are 3-4 standard connectors for trailers and the above linked website seems to detail them well. What sort of trailer are you hauling? Is this the camper trailer you mentioned you are going to rehab? Is the connection just the lights or electric brakes as well? If the connectors on each match then the problem more likely is just the wiring to/from the connectors on the vehicle and/or the trailer. I tow a lot of trailers (boat, cargo, and utility) for work and I rarely find a situation where all the lights work properly - lots of gremlins in trailer and towing wiring that make them short out or otherwise not work. I've had such problems repaired several times in the past, only to discover the gremlins returning weeks or months later. As a result, I always carry a set of magnetic trailer lights (I got mine for ~$25 at Harbor Freight) - this way when I discover a light not working, I can plug these in instead, stick them on the back of the trailer (after verifying they are working still) and I'm legal to get where I'm going and have the time to fix the problems with the main lights.

My guess is if this trailer has been sitting a while that you have faults in the trailer wiring - rain, corrosion, rodents chewing on them etc. Also don't assume the towing vehicle connection is fully functional - these tend to be hooked to or stuffed up under the bumper and take a eating by road debris etc. I usually take my HF magnetic lights and plug them into the vehicle as I know they work - if they function propyl then the vehicle connection is okay and problem is with the trailer connection or wiring.

Let me know if you have specific connector questions but my guess is the trailer wiring needs a good going over. I tthink your original question was wondering how standard the wiring connections on these connectors are and if your problem could be that the vehicle and trailer are wired differently - not likely. These have always been pretty standard IME - you may find it easiest to take the vehicle and trailer to a local trailer or auto electric place and let them slueth it out for you - probably save a lots of frustration.

ss50th wrote:Try this sight. Has all the standards for 4-7 pin styles along with wiring color codes for some types of vehicles.

http://www.etrailer.com/faq-wiring.aspx

Looks like a very good site.
I used to do a lot of this stuff and I want to stress one thing... There can be a lot of wires in any system but the single most important conductor is the "GROUND"... No ground = no results. A weak ground can = all sorts of silly results... ALWAYS check the ground connection first.


.

Dusty: yes, a lot of different connecters have been made.

That chart is a very good one to look at.

Your Ford pickup should have the seven prong plug installed.

I would just buy the matching plug to that and install on the trailer.

What farmer said, check the ground connection, especially the trailer as it

is probably corroded...........

Also, you might as well throw the lights on the trailer in the scrap because, they will be corroded on the inside..

ss50th wrote:Try this sight. Has all the standards for 4-7 pin styles along with wiring color codes for some types of vehicles.

http://www.etrailer.com/faq-wiring.aspx

Thank you very much for the link. This appears to be an excellent source of information and it has answers my original question very well.

Yes, there may be a standard that is in place today and the various manufacturers may comply with that standard but they may not.

Either way, for my specific problem, I am on my own.

The trailer is a 1969 while my vehicle is a 1993 Ford and the other vehicle in the mix (my SILs) is a late model Dodge Ram. He uses the Dodge to haul several different trailers and they all work (but I don't know how many of them have been custom wired).

Bottom line, I'll have to figure out the wiring scheme for the old trailer and wire accordingly to interface with both my Ford and his Dodge.

For the initial haul (to get the trailer from the ranch to my house) I'll build a pair of adapters (trailer to 4 pin flat) and Dodge to 4 pin flat).

Easy job just one I didn't need right now.

Yes, I probably have corrosion and may have critter damage in the old trailer. If I can get enough working (brakes and directionals) I'll fix the rest during the rehabilitation process. We will be on about 60 miles of well patrolled highway getting the trailer here. Those basic features must work before we move the trailer.

Another short-term option is to buy a set of trailer lights for hauling around until you get the issue resolved. They sell them at Harbor Freight and should plug into whatever connector you have on your truck with no problem.

How many wires are on your existing trailer harness? If its more than 4, you're controlling more than the lights and you'll need to wire your truck up for a 7 pin connector. If not, you're looking at a lot easier job.

If you just want to test I would solder (not wire nut or butt connect) in a test lead that reaches the rear of the trailer. Start checking the wires at the signals vs. the test lead for continutiy and resistance. Should be less than 1/2 ohms, but up to 1 ohm will be operational. The ground wire should have 0 ohms through the frame.

The other option is just to replace all wiring and not wonder. I tie the new wire onto the old wire, then pull it through at the other end. $20 worth of wire and 20 minutes of labor and you'll never be chasing gremlims.

The trailer has a 7 pin Bargman connector with flat blades. The truck has a 7 pin Pollack with round pins. Ultimately, I will rewire the truck to either accept both or I will change my truck to match the trailer. Within the group who is most likely to have reason to pull this trailer, I am the only one with the Pollack connector.

The trailer has surge brakes so I really don't need 7 conductors. Four will do it all.

For now, we'll just have to use a truck that has a 7 pin Bargman interface to pull the trailer from the ranch into town.

The trailer is wired properly for the Bargman connector. A couple running lights don't work but we'll be moving in the daylight so that is a non-issue right now.

dusty wrote:A couple running lights don't work but we'll be moving in the daylight so that is a non-issue right now.

Run your hazard lights and you're legal. Someone pulling an old trailer with an old truck is an easy mark for the highway patrol.

If it were me I would simply buy a 7-pin round to 7-pin blade adapter and keep it in the Ford. And a 4-pin to 7-pin blade adapter. That way you can haul either of the modern standards, not just this trailer. Should run $25 for both at O'Reilly. There wouldn't be much advantage to changing the outlet on the truck, I would only do that if I had to run the additional wiring to upgrade from a 4-pin to 7-pin.

If you really don't want to carry those two adapters around, you could go to the junkyard and pick up the assembly from a newer Ford and wire it directly in. Not sure which year would they switched to what you would want but my 2002 has a 4-pin and a 7-pin blade outlet side by side running off the same harness. Just solder it in up stream.