Diagnose this wiring problem with boat to trailer lights

[heavetoo]

The last time I had my boat out the marker lights went out on the trailer.  I had just added new lights and rewired the entire trailer so I was very irritated when this happened.  I was running short on time so I really didn't mess with it.  The brakes and the turn signals worked.


I checked the light hook-up at my truck.  I noticed corrosion on my 7 blade connector and my adapter from the 7 blade to the 4 pin connector seemed worn.  I bought a new adapter that has lights to verify that things are working.


Today I cleaned the 7 blade connector on my truck and removed all of the corrosion.  I also checked the trailer light fuse on the truck and that was okay.  I then plugged the new adapter into the truck and it verified that the turn signals and the brake lights were working.  The headlights weren't working (marker Lights).


I pull the adapter out and check the 7 blade connector at the truck with my voltmeter.  The marker lights weren't showing any current.


This means that the trailer is working correctly, the adapter is probably fine, the fuse is probably fine, but the harness at the truck is not working, right?  I know that it is pretty cheap to replace these, in the grand scheme of things anyway, but I want to get some opinions before I spend any money on this problem.  All the wiring harnesses going into my 7 blade connector seem fine and I don't see any wiring issues.  What could be wrong with it?


Any suggestions would greatly be appreciated!

[gnrphil]

What make of truck ?

[heavetoo]

2008 Toyota Tacoma.

[freezerfiller]

On my truck the trailer hitch has separate fuses from the truck itself so that if the trailer lights blow, you still have taillights on the truck. Make sure you don't have a trailer running light fuse. If you do, check it, not only visually, but make sure that when you put your ohmmeter across the fuse that you have 0 ohms. Sometimes a fuse can be bad, but not blow at the place it is visible.

[gnrphil]

Just getting back to this and I second what freezer said, I spent hours chasing a trailer light problem only for my wife to suggest checking the truck fuses  021

[mosquito13]

Best of luck . Whatever you end up doing, pick up a tube of dielectric grease and apply at every connection .

[985crabs]

I'm going with a secondary fuse too. I borrowed a buddy of mine's landscape trailer a couple/few times and I noticed that after using it my boat trailer lights wouldn't work right. There was a trailer light fuse blown in the double-secret fuse compartment under the hood.

It turns out his trailer had a bad or intermittent ground in the wiring. All would be well for a while then the problem would manifest itself and blow my fuse. I'm mentioning this because you just rewired your trailer and added the marker lights. I'd revisit all of those connections and make sure they're solid, greased and sealed. Do you markers self-ground on the trailer frame? Make sure there are good contact points. Then find that fuse in your truck, replace it and try your trailer again.

[heavetoo]

So I ended up wiring in a new truck wiring harness. When I was wiring it I noticed that the wires for the new harness had different color codes to the truck wire harness. I put my adapter in, that has a tester, and verified that I was connecting the right thing when I was connecting the wires. I came to the running lights.

Earlier I had pulled the fuse in the area under the hood. The fuse wasn't blown and if it was the brake lights or turn signals wouldn't work.

Going on I hooked up what I thought was the running lights (meaning the lights that come on when the headlights are on) and I didn't get anything on the adapter/tester. By that time I had already wired all but two wires. Long story short I ended up wiring the auxiliary wire which has continuous power to the running lights. The running light wire is still not showing any voltage.

This means that my running lights are always on. The turn signals, hazard signals, and brakes still work. This is a temporary fix until I can figure out why the running light wire isn't running voltage.

So it comes to the question of WHY one particular wire isn't showing voltage when everything else is working correctly?

The last time I used the boat trailer everything worked correctly until I started going home. The running lights went out on the very short half mile trip home. They worked going in and out of the water. I don't know why it just suddenly stopped. There wasn't any on/off stuff going on like a classic short. It acts more like a blown fuse but the running lights are on one circuit with all of the trailer lights according to what I saw in my owners manual.

[freezerfiller]

Did you check the 30A tow/tail fuse under the hood with an ohm meter? did it read good?

[heavetoo]

Yes, but finding stuff on Toyota is a pain in the butt. I read where there may be a third location for fuses for trailer wiring and I checked several areas but I couldn't find it. I also saw one more fuse in the fuse box under my hood to check. The fuse I checked under the hood was good and it had perfect current.

Even figuring out what each fuse is can be difficult. Their abbreviations are horrible. If you read on the Toyota forums it gets confusing because each year it seems like there is something different. In an 06 there is a fuse box behind the rear seat but it doesn't exist in my 08. In another truck there was a fuse box in the area where the jack was located under the passenger rear seat. Still others have a third location under the hood.

It would be nice if things were more straight forward.

[heavetoo]

SOB!!!!!! It was a fuse. There is a separate fuse in the fuse box under the hood for tail lights. It is abbreviated so it was hard to tell that it was the trailer tail lights.

Anyway, it was a 30amp low profile fuse. I was able to buy replacements.

So, tomorrow I will fix that wiring issue on the harness and switch the auxiliary wire and the running light wire so it is wired correctly. Then all should be good. I have some spare fuses, let's hope that I don't get an issue with blowing fuses now.

[985crabs]

Sometimes finding the fuse is 3/4 of the battle.

Hopefully it is an isolated incident and you don't have to find what caused that fuse to blow.

Good luck.

[AHHHH-Spray]

Apr 17, 2018 14:40:34 GMT -6 heavetoo said:

They worked going in and out of the water.

Unplug your trailer lights before you dunk the trailer and plug them back in before you head home.

[freezerfiller]

Glad you found it. I've had that problem before and more than once, usually it happens when I try to plug in the connector when the lights are on and if that ground pin from the trailer plug hits the taillight pin on the truck... poof.

[heavetoo]

Funny you should mention it, because my last adapter was not right when I got home and I replaced it. The ground part came loose and was barely making contact so I am sure that it was in and out. Let's cross our fingers that was the issue there.

Now to just switch those two wires and I am golden.

Thanks for the moral support and help!!!

[heavetoo]

Finally I got it.  I got the fuse in, rewired the harness to the correct wiring configuration, and then I added new LED marker lights (I had an issue with one of my old marker lights).

I had another issue with the ground at my driver's side running light on the trailer.  Figured out the ground was bad so I re-did it.  Now everything is working flawlessly.  I really like the LED lights on the trailer and I like my new plug.  I guess it was worth it in the end.

I am looking at my rollers now.  Seriously, in the next year I would really like to switch from rollers to bunks.  I need work on my rollers soon and I would just rather replace them for bunks.

[985crabs]

Glad to hear it.