Trailer light connection issues

^^^This^^^

Myself I would have done this many steps ago. Either find someone with a known working truck and put your trailer behind it, or find someone with working trailer lights and plug it into your truck. This will narrow greatly where the problem may lie.

 

Problems abound in both. Major crapshow

I just plugged in a "NEW" oem converter unit and it behaves identical to the old one as evidenced by the test plug.

Blinkers work unless the tail lights are on. Then only the tail

So unless this failure is related to Time not Usage, I dunnoes. I had a volvo s70 that was known to have ABS module failure at 15 years regardless of mileage... right on time. Was a pair of capacitors. Wonder if this is something similar. Amazingly this unit appears to pop right open. The abs module had to be cut

Yes. The aftermarket unit is always an option. I just Really hate chopping into the harness. Straight up dont wanna do it. Always makes problems within a few years...

 

Uy
Well i just cracked open the new one and assuredly made it non returnable. All 4 clips snapped off and the side of the case. Lol. Wasted money is fun.

I see nothing that looks like a time related failure point besides possibly one big flat cyinder that might be a capacitor.

Its weird. Its drowned in a super sticky stretchy silicone heat gel. Got stuck on my finger and pulled 2 inches before snapping back to where it came from




Its all so weird. I dont understand why this module has anything at all to do with the tail lights. Its irrelevant. Im of half a mind to cut the tail wires at the converter and twist em together

 

So. The circuitboard sheds some light on the wiring.
I see
RT-right turn
R/S-right stop
ST-stop
NC- (WHAT IS THIS)
TL-tail
TL-tail (not specified in or out) they are actually directly connected by a block of circuit trace.
L/S- left stop
LT-left turn

And GND by itself on the little plug

Perhaps i should pull the gnd and see if it changes anything or if it continues its odd operation. Coukd be telling

But wtf is NC?

 

NC on a terminal generally indicates No Connection. It is an extra pin in the plug, perhaps to make it compatible with other interchangeable options, or to be a unique size so the wrong thing cannot be plugged in.

 

Of course the haynes manual makes zero mention of this curcuitry or module

 

Thanks.

 

I just went and yanked the ground plug from the converter. It exhibits similar behavior except that the tail indicator on test plug then blinks. It is steady otherwise.

The NC in fact has no wire in the plug.
Thanks

Im really feeling inclined to chop the tail wires out of the module

 

Uy does anybody know the location of where the white trailer ground wire connects to the chassis?

 

This is an older design... do you happen to have LED tail lights in your truck or in your trailer? Sensing functions may not work right (just like some flashers won't work right) if it doesn't detect the loads.

I would start by following the wiring from that box to the trailer connector and see if there are any other plugs that need connections cleaned up. It has been a long time since I installed the factory towing package on my '04 so I forgot if there was or was not a plug in the harness under the bed.

I might also whip up a mock trailer. You'd need a trailer plug pigtail, a couple 1157 bulb holders with a ground tab, and a couple 1157 bulbs. Strap it to a block of wood and make the connections so you know the trailer side is right, and with real loads, while you test.

 

Led in the trailer only
This does not seem to be the issue
I have definitely seen thermal blinker switches get wanky with led though.

The mock trailer is an interesting idea
Probably wind up installing the lights on the real trailer in the end.

I tried my damnedest to separate the harness plug under the bed that goes to the 4flat. It may have some rustproofer in it but it seemed strangely complex. Couldnt figure out how to un latch it

I may wind up doing the 7 pin swap too. This 4 flat business is such junk

 

Harbor frieght sells a (mobile) magnetic trailer light/set/kit. Plug them in attach magnet lights to your metal rear bumper I use them saves from hooking up an actual trailer for lights

 

For troubleshooting purposes on different vehicles

 

It gets weirder
The ground is good.
It tests 0.00 ohms from the white wire to the bumper. Like the ground is Real good.

I cut the test extension i had built and verified that nothing is finding a ground through the taillights. Its dead dead with the white cut.

I put that back together.
Cut the tail wires at the factory converter as ive been threatening. Twisted them. Eliminated the potentail for interference in the box. No change. Whatever the issue is... its coming from elsewhere in the system.

Hell if i can guess why any of it affects the trailer output and not the back of the vehicle.
All lights work perfectly on the truck

 

Perhaps weirder yet
I disconnected the plug from the converter.
Turn on flashers.
The flasher inputs to converter have pulsing voltage. As tested with multimeter and led test probe.
Turn on taillights. I still have the same pulse at the plug.
Yet even with the tail wires cut
When plugged back into the module,
the taillights still interrupt the blinkers

Even with a ground directly to the battery.

And with brakes applied everything looks good. But the blinkers are then acting as an interrupt not a power circuit

Demons.

 

I just jumpered between the blinkers and the stop/turn outputs at the plug to eliminate the converter.
The blinkers blink on the test plug in the back and on the test probe poking the jumpers.

Tail lights kill the blinkers at the back but they are working at the jumpers

 

Oy.
Well now

I bought a new test plug.
It looks rather normal


I bought a fresh pair of harbor freight led taillights. Hooked em up on the trailer. Nothing.
Tested the ground wire on the trailer to the truck bumper with the meter. Nothing.
Jumper cable from ground wire to bumper still nothing. Yanked them off the wagon and made Fake trailer with brand new harness... bingo.
Something is dicked up in my new trailer wiring that shall be ripped out tomorrow and re- redone. Maybe the connector.

Think im also gonna install a 7 pin socket on the truck just because it looks more weather resistant. The truck does have a trailer brake controller so 7 pin seems like a great idea even if ive never even seen an electric trailer brake in person. Lolz

 

Thanks for your ideas guys
Sorry the situation turned out to be as mundane as a bad test plug and a bad trailer plug. Lol