I have a 91 Pickup V6 pulling a enclosed utility trailer. The truck has the Flat 4-way electrical end which needed a adapter to fit the trailers 7 way female end. The problem is, is that the trailer's lights are very very dim when plugged into my truck, and only come on very very dimmy if the truck power is on, WITHOUT the engine running. As soon as I start the engine the dim lights go out. So far I have tried:
- A new adapter
- A new Flat 4-way male end on the truck end.
- I made sure I had a very good ground, (tried many different places).

The trailer lights all work. I hooked the trailer to another vehicle and everything worked great.

Any suggestions?

Thanks for reading

 

Is there a converter installed in the truck for the 4-wire connector? If not, how is that wired in? Toyotas generally need a converter to split out the combined bulb signals and re-combine them for the trailer.

 

I'm not sure. All the wiring is taped and housed together underneath within the side panels. The wiring that comes out of the end had been hooked up to an old Flat 4-way connecter by the guy who owned it 10 years ago. So I hooked up a new one and nothing changed. There was an extra wire (red) coming from the truck that was grouped together with the brown,yellow,white, and green wiring that matched the 4-way connections. The red I assumed was for the brake lights that could make it possible to hook up a 5-way flat connection but I'm not sure. The previous owner had the 4way connector hooked up and it seemed like it got a lot of use, so I could only imagine that it worked for him at one point. When I did strip the wiring, the copper was black, would old wiring not be giving me enough power? I'll test the voltage coming out of them tomorrow...

 

Sounds like that may be the issue. You generally need to have a 5-wire to 4-wire converter between the vehicle lights to the trailer plug. My '85 has a converter from U-Haul installed in back. Has the connections from the vehicle feeding the 5 inputs and the trailer plug coming out of the other end. Might be the PO may have had a trailer set up to work with the existing wiring, The problem generally is that you have separate turn signal, brake and running light bulbs and the trailer does not.