Trailer lights driving me mad

[Slartibartfast]

'93 Pathfinder, mostly stock. The trailer lights worked just fine when I got it, but now they're acting up.

 

It came with a draw-tite converter box. I plug in a trailer and all functions (brake light, running light, turn signals) work. But when the running lights are on, you can barely see the brake or turn lighting. If I put the turn signal on, you can see one side dimming as the other tries to flash. At night, I can barely see the hazard lights if the running lights are on.

 

It looked like a bad ground, but testing with a new ground didn't change anything. My second thought was that the trailer wiring was wrong, but if I test directly from a battery to the trailer plug, the trailer lights work great. I tried the truck with a different (known good) trailer and its lights became strangely dim too. That means the problem is in the truck.

 

I assumed the converter box was bad and got a new one. Same problem. I thought maybe the PO's nasty suitcase connector install might be screwy somewhere, so I rigged up test leads from the wiring to the box. Still no change. The truck's running lights and turn signals work great whether there's a trailer installed or not, so whatever is bottlenecking power to the trailer is not affecting the truck's lights--which is weird since the trailer light controller tees right into the tail light harness.

All I can figure is that the convertor isn't getting the power it needs somehow, and the only thing I've really messed with in between it working and not working was the dimmer, which has started to fritz again lately (dash lights don't always come on immediately). Seems entirely unrelated but it looks like the running light wire going to the driver's side tail light is pink with a blue stripe, which I've only ever seen going to the bulbs in the dashboard switches and cluster. I need to study the manual to see where exactly that wire goes.

Anyway, I'm pulling my hair out trying to sort this one out. Anyone got a bright idea?

[adamzan]

I had a similar problem, it was the ground that supplies ground for the taillight harness itself. Tiny ass black wire. FYI, there are a lot of pink wires with blue stripes on these rigs.

 

Where you at in WA? I'm currently passing through.

[Slartibartfast]

The convertor grounds on the body, and I ran a jumper from the body to the wiring on the trailer with no improvement. It sure looks like a bad ground but it seems like that should've cleared it up if it was.

 

I'm in Winthrop, let me know if you're around.

[adamzan]

Are all the bulbs of the right type. Sometimes people put in what ever they find.

[LittleFR]

Try running a direct ground from the trailer to the truck. The trailer lights may be getting a crappy ground through the ball (if the ground wire isn't solid to the lights)

[Slartibartfast]

Trailer lights are brand new and the bulbs look like standard 1157s to me. They light up just fine when I power up the trailer harness directly. I've run a test lead from a body ground in the truck to the ground screw on the trailer frame with no improvement. I even tried running the jumper all the way to the light housing to rule out a bad ground between the housings and the trailer frame, no change.

[Slartibartfast]

Alright, ruled out the trailer completely. The trouble, whatever it is, is with the truck.

 

There's a weak circuit somewhere. The trailer light convertor had its own body ground, so the body ground for the tail lights should be irrelevant to its operation. It's gotta be on the positive side. The tail lights dim slightly when the blinkers come on, and the interior lights (all LEDs) dim slightly as well. Battery is fully charged, fuse links look okay. My voltmeters are worthless for testing blinkers (analog sweeps too slow and digital refreshes too slow) but I've got an old dashboard voltmeter that's quick enough to give me some idea of what's going on, and it's slowing the rear blinkers down around 10v (at the truck harness, no converter plugged in) if I run the hazards and the running lights at the same time with the engine off. With the runners off, it looks more like 11v. On the running light circuit, the meter shows a small drop when the hazard lights are on, but it's less than a volt. At the battery, it barely moves.

 

If I hook constant + to one of the brake/turn filaments, that light will blink opposite to the lights on the truck. Clearly not enough current to go around. Really seems like it has to be a ground but again, the convertor had its own ground and didn't rely on the harness, and it still didn't work, so I'm starting to wonder about flasher units, fuse links... I cleaned the battery terminals, checked the relevant fuses, checked a couple fuse links, no smoking gun yet. The next test I need to run is checking for power between the harness ground and the body to rule that out, then from blinker + to a known constant +... then to stare at the EL section until I figure out how all this is hooked up and what between the battery and the lights is causing problems.

 

 

[adamzan]

What about the ground on the battery cable that is bolted to the body? Mine was loose/rusty. Cleaned it up and it fixed a few problems. One being my temp gauge would move with any electrical load.

[Slartibartfast]

Battery ground bolt snapped when I went to check it! With the surfaces clean, and a new bolt, nothing's changed with the lights.

 

The running light circuit tests about 1v lower than the battery when I test at the rear lights. The front markers test low too. I tested at the switch with the lights on and it shows lower voltage than the fuse box, but not as low as it is in the back. I bypassed the switch with a piece of wire jammed in the plug, no change, so it's not the switch. Cleaned the switch because I was in there anyway and found some discoloration around the marker contacts, not sure what to make of that, but it's clearly not the problem. Checked the fuse link on the battery, nothing wrong with that. Seems like something is wrong between the fuse link and the switch, but hell if I know what that would be--I'll have to do some research and see what I can come up with. I'm thinking I might run fused + from the battery to the running light circuit at the headlight plug and see if that works--if it does I can rule out the wiring between the switch and the tail lights. All I can think of at this point is that something is drawing too much power and overwhelming the tiny little wires Nissan used for everything.

 

On the plus side, a good scrub with 800 grit got rid of the chalky oxidation on the headlight switch, so at least something's better than it was when I started.

[Slartibartfast]

A year and a half later, I finally fixed this!

 

I did some research and found out the little tap-in light converters just kinda suck. Cheap transistors, lots of voltage drop. I'm sure the angel hair wiring to the truck's tail lights wasn't helping matters, either. I ditched the Draw-Tite box for a homebrew agglomeration of relays with its own fused power feed from the battery. This means the trailer is isolated from the truck's lighting system, and can't pop anything but its own fuse if it shorts out. Lights are much brighter now! Only downside is that the cheap relays are a little noisy, but I installed them with a switch so I can shut them off when I'm not towing.

 

If anyone's interested in hearing me talk for far too long, I put up a video explaining how it all works.

[adamzan]

Interesting. I've never had a problem with mine, maybe because I have one of the ones that plugs in to the tail light connector (which then plugs into the tail light)?

 

I assume you don't have a brake controller in yours though?

[Slartibartfast]

Nope, no brake controller. I set mine up so it plugs in between the brake light harness and the light because I had a couple extra plugs and hate Scotchlocks, but I doubt it made much difference to the electrons.

 

Looking at the numbers, I'm noticing that the voltage output from my relay setup is actually higher than what I tested from the wires tapped into the factory tail lights when I was testing the old converter. The brake light signal out of the fender tested as 10.27v; the new relay setup gave 11.20. (This is not with the engine running. I should've checked the battery voltage both times, but of course I didn't think of it until later.) The tail lights work fine, but this does make me wonder whether that volt or so of drop is just because Nissan used tiny wires and I'm using a 14 gauge line or if something else in the lighting circuit isn't as healthy as it should be.

[adamzan]

Its weird, mine are nice and bright. Perhaps youve got a ground issue somewhere. The wires are small but more than enough to power 1157 bulbs.

[Slartibartfast]

That was my first thought at the time, and something I blew a whole lot of time checking. At one point I think I even ran a conga line of gator clips from the battery to the trailer. Made no difference.

 

That said, the next time I've got a minute I might check the ground from the headlight harness against another body ground and see if there's any drop there. I probably did this before but now you've got me thinking about it again!