Looking for some help with wiring a trailer light plug.

I have a 1975 F250 that I will be using to tow my boat. I recently finished installing a completely new wiring harness from bumper to bumper. My boat has a 6 wire round connector and so does the truck.

My questions:

1) Since the wires from my new harness are labeled, can I simply splice into the wires for right turn, left turn, brake and tail and match them up to the plug wires that correspond to these on the trailer?

2) I recall that the flashers seem to flash faster when the trailer lights are hooked up. Is there a better flasher that is recommended to eliminate this?

Gotta get my boat on the water!

Thanks.

 

For your first question, it depends on how your trailer is wired. I am not familiar with the older 6 pin connectors and have never used one or wired a trailer with one, but I doubt they are that different than the newer style ones. If you have separate tail lights and turn signals then you would be fine to go ahead and wire them up wire for wire. If, like most modern trailers, you have a "stop/turn" as they call it, which is where you have only 2 lights on the rear and they are both dual filament, and one filament is the running lights, and then a second filament is both the brake light AND the turn signal, then you will need a controller. I guess its theoretically possible that your trailer would already have one integrated into the wiring, but I've never seen one that way. Usually the stop turn controller is behind the plug on the truck. The stop turn controller should have a resistor in it that would keep your turn signals from blinking too fast as well.

 

LMC Truck Parts - Page 81

Can always cut the end off to wire the trailer brake plug in.

 

Yes you can splice, only if you have the old separate trailer lights like hasteranger said. However you do it, PLEASE DON'T USE SCOTCHLOCKS. Do it right, use butt connectors or solder that ish in there. Scotchlocks are gonna corrode on you in like a year if you live where they salt the roads. And you would be totally ruining that new harness that you just put in.

2) You need another resistor, like hasteranger said. The reason it blinks faster is because you have created a parallel circuit, decreasing total circuit resistance and increasing total circuit amperage. This is the same thing that happens when a blinker goes out, your blinkers blink faster because one of the filaments is burned out, and there's less total resistance.

 

maybe i got it wrong, but doesnt a 75 just have a stop/turn in the rear?

that is to say the same bulb is the running/stop and it just blinks for the turn signal.

i know my 79 is set up this way for sure. if that is the case, just splice into the circut to make the connection. the trailer lights will do the exact same thing that the truck lights do.

if not and you have separate brake and turn lights on the truck, then you will either need a converter, or i could tell you how to do it with two relays, but the converter would be much easier.

if your flasher is going bonkers with the trailer hooked up, just get an electronic flasher. any parts store should have one. the electronic flasher controlls the flash cycle electricly instead of thermo-mechanically. It will just flash at a set rate regardless of the electrical load on the flasher. should only cost 10-15 bucks for the flasher unit. Had to do the same thing in my Crown-Vic ... worked like a charm.

 

Yes, this is correct.


I will look into this - thanks.

 

Butt splice w/heat shrink is the only way I splice wires on my truck.

 

Thanks. I honestly cannot remember if I have separate tails and turn/brake on the trailer. Guess I need to check that out.

 

freeford who made your wiring harness?

 

Painless...

 

I used to be the same way, but 3m makes these really nice T taps that are a spade connector that I've had pretty good luck with. They are filled with dielectric grease to seal the connection once you splice them. I've had as good of luck with those as I have with a soldered T splice.

i also really like the new fusion tape they have, you wrap it around something and it forms a solid layer of rubber as it fuses to itself. Its way easier to use than heat shrink, especially on a T splice. Heat shrink can be finnicky.

As for the question about whether are trucks are set up that way, now that I think about it, i believe that is correct, that the trucks are already set up with stop turn lights from the factory. I haven't really done any work on a truck with stock lights, though, since mine has a flatbed, so I couldn't say for sure.

 

I'll just add, to fix the "fast flash" after splicing in the trailer wires and hooking up the traier, you need "heavy duty" turn signal and flasher units. They are avaialble at any autoparts store for $5-10. They will plug in to the harness under the dash. They look like a small round can. To find them, you can activate the turn signals or flashers and trace the sound they make.

The only drawback of the "heavy duty" units is they won't warn you if a bulb is out by a "slow flash". As long as you check your lights from time to time, no problem.