LED Trailer Light Question - Towed by my 200

[CharlieS]

For lots of years I was a pickup truck guy, loved having the convenience of a truck bed. Then I fell in love with Land Cruisers, and found I used a truck bed like once a month or so. My solution was the land cruiser plus a trailer.

So, a handful of years ago, I sold my last truck and started using a 4x6' trailer with my 200 to fill this gap. It was a cheap used thing with a steel frame and incandescent lights. It got the job done.

Over time, I got sick of chasing lighting problems every time I used the trailer - bad ground, blown bulb, mouse chewed wired, corrosion. So, I went out and bought a high quality aluminum trailer with LED lights all around - life was good. Everything worked, the lights were dead reliable. No messing around when I used it.

That worked for years. But, recently I had a passenger side marker light on the fender go out. This lens is a red rear, yellow front side marker whose receptacle is riveted to the fender. The light is the style with a removable lens module that contains the LEDs, and a fixed receptacle. It has both a positive and a negative terminal (like bullet connectors) moulded in - so it is not grounded through the trailer frame like some lights.

All of the other lights (including the drivers side marker) still worked correctly, as bright as intended.

So, I bought replacement lenses that matched the original equipment part number:

Optronics MCL61ARBP Amber/Red LED Fender Light

Optronics MCL61ARBP Amber/Red LED Fender Light

Optronics MCL61ARBP Amber/Red LED Fender Light

www.amazon.com

I plugged the replacement in, and it worked but very dimly.

I cleaned the trailer side receptacle with Deoxit, worked it in and out with a spare bullet connector, and then some very fine sandpaper, and made sure the female pin receptacles were making a tight connection.

I checked for voltage and got 12.67 volts.

I plugged the new unit in and unfortunately I still got the same result - the passenger side marker light was on but the bulbs were very dim.

I swapped the light modules driver and passenger side - and the both the new and the old light modules were appropriately bright when they were on the driver side and very dim when on the passenger side. This leads me to believe the issue is not the replacement lens/light assembly, but the trailer side of the system (at least on the passenger side marker circuit).

I am admittedly not very electrically inclined, but with other LEDs, I understand that adding a resistor dims them. So I'm wondering if is it possible that I have some sort of electrical resistance that has built up in this circuit that is causing the dimness? Maybe a corroded wire, pin or connector? Or a poor electrical connection that is making contact, but not solidly?

Thanks in advance for any guidance you can provide.

 

[lx200inAR]

Do you get the same 12.67 volts on the side that works? Also, i'm assuming you are checking the volage from one pin to the other in the connector? I agree with your assumption about a compromised wire/connector. I would say you could start tracing down resistance from the hitch plug back to the light receptacles. But unless my physics are wrong, if you had higher resistance between the two connectors, you'd also see lower voltage. So, if you see the same voltage on each side, it seems like it would have to be the connector at the light receptacle vs cabling between the hitch plug and the receptacle.

 

[linuxgod]

Start by just attaching the negative wire on the light to the frame (assuming your trailer is negative ground, which is likely but I’d double check). If the brightness improves, it’s an issue with your negative wire somewhere (but you don’t need that wire if you ground to the frame).

Keep in mind when measuring your voltage may be 12.67 but there’s very little amperage measuring with a multimeter. You’ll get the same voltage if you have a wire that’s frayed but still partially connected. You can only really tell if it’s a good connection by pushing a bunch of amps through the wire and watching if the voltage drops significantly.

Lastly, it’s possible one of your lights is constant voltage and the other is constant current. I’m not positive (haha) that would cause your issue but it might. Constant current LEDs are more typical on 12V systems as they’ll always have the same brightness no matter what the voltage is (within reason - typically about 9V to 15V or so).

 

[CharlieS]

Do you get the same 12.67 volts on the side that works? Also, i'm assuming you are checking the volage from one pin to the other in the connector? I agree with your assumption about a compromised wire/connector. I would say you could start tracing down resistance from the hitch plug back to the light receptacles. But unless my physics are wrong, if you had higher resistance between the two connectors, you'd also see lower voltage. So, if you see the same voltage on each side, it seems like it would have to be the connector at the light receptacle vs cabling between the hitch plug and the receptacle.

I'll have to do some more testing to be able to answer. We just got a big dump of snow, so it may be a couple of days.

Thank you for the advice and guidance.

 

[CharlieS]

I wasn't able to test the trailer tonight, but I did some basic testing.

I made two jumper wires with male
and female bullet connectors.

I put this on a spare car battery in the garage and it lit up bright as can be.

The funny part is that this is the original (presumed) dead/blown light. Oops.

I put a 7 pin to 4 pin adapter in my 200, and put this setup in the ground and parking light pins - it lit up as bright as can be.

So there's definitely something going on with my trailer wiring or the receptacle. No big surprise, but at least more facts to work with.

I verified that the old and new part numbers match and the old and new part numbers light up bright when direct connected to a car battery.

 

[GordJ]

Whenever I have an 'interesting' electrical issue I almost always find that the problem is discovered to be the ground. Just a rule of thumb.

 

[Sandroad]

What type of connectors are used on the trailer? If they are the clamp type, those are notorious for corroding and failing either slowly or completely.

I assume the trailer is a 4 pin connector. Have you looked at the backside to confirm the seal with the wire and connector is good. If that gets leaky (technical term), the wire connections inside can corrode and fail. Same thing on the truck side.

 

[CharlieS]

What type of connectors are used on the trailer? If they are the clamp type, those are notorious for corroding and failing either slowly or completely.

I assume the trailer is a 4 pin connector. Have you looked at the backside to confirm the seal with the wire and connector is good. If that gets leaky (technical term), the wire connections inside can corrode and fail. Same thing on the truck side.

I think the trailer side connections are waterproof type crimps. I'll double check.

Yes, the trailer is a 4 pin connector, and I have a 7 pin to 4 pin adapter. Another thought is I need to swap that adapter out to rule it out as a potential issue. I have a couple of different 7 pin to 4 pin adapters I can try and I'll check it with my multimeter too.

I like the corroded 4 pin theory, I'll dig into it.