DIY: MFI Trailer Wiring and Backup Flood Lights

[KXCam22]

Face it. The MFI trailer wiring and lights are crap. The first summer I had my boat I spent more hours working on the trailer lights than on the boat. I did two things to fix this. LED lights are a must since the stock waterproof lights I had only succeeded in keeping water in. The seconds was to install a dedicated ground wire down each side of the trailer and connect it to all the lights. This prevent any corrosion induced grounding issues. Here are some wiring diagrams I made. Hope they are helpful. Also note on the ultimate wiring diagram the additional backup flood lights. I added these to help when backing into camping spots in the dark. They also work under water when loading the boat in the dark. Cam

 

[Bruce]

Those are impressive diagrams!

I am curious why you hooked up your backup lights to pin 4 with a switch instead of 7?

I run a pair of backup lights off of pin 7 on my utility trailer. Were you worried that there might not be enough amperage to disengage the brake and light the bulbs?

 

[txav8r]

Very nice Cam!

 

[leatherneck33]

I would like to setup the backup lights, what lights did you use? Thanks for posting your setup.

 

[-klb-]

I would think that using pin 4 is so that you can switch them on and leave them on while loading the boat at night.

I might consider using a double throw switch to select between pins 4 and 7.

 

[KXCam22]

KLB is right. Pin7 is the always on trailer power wire. I only use them in reverse when I choose and with the switch they will stay on with the truck lights off. The lights are just cheapy sealed beam tractor lights, $5 each but sealed so they work underwater. In theory I think they are too powerful to legally be used as reverse lights on pin 4. They lights have proven to be extremely handy. I was rewiring anyway so a couple of extra wires pulled was easy and there was a natural no-work required mounting spot. Cam.

 

[Scottintexas]

great write up, thanks for the diagram, for others in the future if you're having trouble with a ground on a trailer with a folding tongue you can try run a jumper from near the hitch where the connector grounds around it to the ground of the first marker light,

 

[Julian]

@KXCam22 What brand/model LED lights did you switch to? Just had my first light failure (11 hours from home of course) and now need to buy some LEDs to replace the stock turn/brake/running lights.....

 

[KXCam22]

I used some cheap Grote ones. A friend works at a peterbuilt shop and got the over 80" trailer kit for me cheap. They fit (with a few bolt hole mods), they work and they still work today - haven't looked at them for 2 seasons at least. I haven' replaced the small side marker lites yet. Those seem to hold up. My stock MFI lites were beyond horrible. I even replaced the ones on my dirtbike trailer a week later just to avoid any future maint hassle. Its a worthy switch. The LED optronics are nice and a perfect bolt on. They were ridiculously expensive in my town, hence my using the Grote kit. The Grote lites are the same size as the stock ones but required drilling one different attachment bolt hole. This is the kit.

Cam