LED exterior light conversion! not going well :(

1985 Chevy C10

so I decided to do the switch to LED's because I was having this same issue with incandescent so I figured LED's might solve the problem BUT, boy was I wrong lol

so at this point right now all of the exterior lights have been changed to LED's., including the LED Flasher module located in the fuse box.

I purchased new side marker housings with LED lights already installed inside the housing for the front and rears off of AliExpress, reviews looked good and people have plugged them in and good to go!

these new lights, they have a red and black wire, but as I understand the side marker lights are both hot., blue for the signals and brown for the parking lamps. either way I plugged them in so the red is on the blue side of the plug and the black goes with the brown.

So, my issue is this. With the headlights off, all lights and turn signals work good except the side marker lights.,
the rear side marker lights are lit up as they should be but the fronts are completely off, no signal flashing

next, when I turn the headlights on., the front marker lights turn on but are very dim/barely lit up., when I turn the turn signals on the front side marker lights flash as they should.

so with headlights off, the front side marker lights do not flash with the turn signals

with the headlights on the front side marker lights do flash with the signals but the DTR lights are dim/on but barely visible.


I also notice that when I turn the headlights on the dash turn signal light indicators illuminate very dim/barely on just like the front side marker lights do.

also, I notice the front drivers side marker light wiring has two wires, a light blue wire and a brown wire, they both go into a harness and travel to their respect location but the brown wire has a split/joint wire attached which is also brown and it's just hanging and not connected to anything. doesn't that wire need to be connected to the turn signal parking lamp wire? or is that possibly there and was used to feed some other light system? for say, fog lights or something?

anyway., Im completely stumped and can't seem to figure this out

I noticed this forum has a lot of pros here in the electrical vehicle system so I'm hoping to get some help in figuring this mess out., what steps I should take? should I try and go back to all incandescent bulbs and see if its a LED issue? maybe I need resistors in line somewhere?

or should I just re-wire the front side marker lights directly to the front turn signal lights!?

let me know if there are anymore details that can be helpful to figure this out!? thank you!

My opinion is to go back to incandescent- at least until you get everything working correctly. LEDs add a few more layers of problems to figure out. First thing- make sure you have good & correct bulbs and the sockets look good. (Front turn signals are 1157, they a dual filament which is very important).

ChevyTruckLove75 said:

blue for the signals and brown for the parking lamps.

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That is correct. The original side markers blink the same as the front signals with the headlights off. They alternate with front signals with the headlights on. With the headlights off- current goes through the (flasher) blue wire and grounds through the brown (through the dual filament front bulb)- they blink. With Headlights on- current goes through the brown wire and grounds through the blue wire (through the dual filament front bulb) for the parking lamps- however when you turn on the signal- it feeds current (flashing) down the blue wire- since current is coming from both direction (brown & blue wire) it causes the bulb to go out every time with the flashing current. Think of a garden hose with water coming from both direction- water will meet in the middle & not flow.

So when you add LEDs to that situation it gets confusing - LEDs only let current flow in one direction unless its been modified somehow.

Let us know what problems you are having with incandescent- if you go that route. Most light problems are usually cause by wrong/bad bulb or grounding issues.

Thank You for responding! I really appreciate it!

yes that explanation makes perfect sense and I totally understand it!, however, my situation is strange because Im having the dim lighting on the side marker lights when they should be bright like the rear marker lights., the only time they get the same brightness is with the turn signals on and the headlights on at the same time!
while its flashing bright., as soon as I turn off the turn signal it goes back to being much dimmer than the rear side marker light.

and also when the headlights are off and I turn on the turn signals the front side marker lights dont flash., front signals and tail light signals work fine!

also the brown split wire I have leading to nowhere from the drivers side marker light.,. is that factory? I would take some pics but its been pouring rain outside for the last day and a half but I will get some

Yes, please go back to incandescent.

I work at a shop and we do a lot of work on older rigs and classic. LEDs are in my opinion a nightmare to get and keep working correctly on our older rigs if your ever even able to get them to work correctly. If a vehicle like ours comes in LEDs and there is an issue with the lights working, one of the first things we'll do is put it back to incandescent and troubleshoot from there if needed.

With that said there are a couple guys on the forums that do like LEDs and might come along and help you, but my advice is go back to incandescent and troubleshoot from there.

Is this with LEDs or incandescent? LEDs get confusing like I mentioned- They typically only let current go through them in one direction. AND the front lights depend on dual filaments that lets the opposite filament being used act as a ground- which can also be problematic with LEDs. ALSO electricity looks for a path to ground and it can do some strange things if it finds one it isn't really suppose to be using. Is it doable with LEDs- Yes, but If you were having problems before with incandescent- you should get that fixed before moving on to LEDs. (my opinion)

ChevyTruckLove75 said:

also the brown split wire I have leading to nowhere from the drivers side marker light

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For me it would be easier to tell with incandescent. If all your parking lights worked -I would say it was just added on- If they don't, we could trace where the wire was suppose to go to.

Here is a LINK where you can download the wiring diagram.

Forgot to mention- tail lights are a more simplistic setup than the front. It usually isn't difficult to change them to LEDs.

Go back to incandescent bulbs and #1 rule of anything light/wiring related on these trucks are......say it with me class

Check your grounds!

Yes that's right, always check your grounds. These trucks are notorious for having ground issues that will and have caused a lot of grunting and frustrating troubleshooting along with some very colorful language at times! From what you're saying, it appears that it very well can be just a ground issue. Check with a meter to check for continuity between the bulb socket ground and the radiator support where the ground wires are located to make sure that you've got a solid ground between the both. Make sure to do this on both headlights and turn signal sockets. If any of these are a weak link, you'll get some really weird results of bulbs being light, not being lit, only partially being lit and just in general weirdness.

amazing info guys!! thank you, I certainly have some ideas to look into ., first thing Im going to do is swap all the bulbs back to incandescent first and foremost!, then Im going to check that ground like a MF! and make sure the grounds are connected good!
I wanted to ask one thing tho, I was doing a little research earlier and read somewhere about possibly the headlight switch itself could be faulty and causing an issue.,? I know that my light switch feels a little weird when I pull it to the first step (parking lights). sometimes I have to jiggle it to get it in the sweet spot otherwise the headlights turn on almost immediately. I ordered a new switch anyways so I will try that but definitely after I remove all the LED's and replace the incandescent bulbs!

I'll keep ya's posted on the results!

LED's are basically a computer circuit. None of the OEM parts on SB were designed for it. Any resistance not going to work.

ChevyTruckLove75 said:

I wanted to ask one thing tho, I was doing a little research earlier and read somewhere about possibly the headlight switch itself could be faulty and causing an issue.,?

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Probably not causing your issues. I wouldn’t ever say definitely not, strange things happen - but very doubtful. Sounds like the switch is wearing out, so it is smart to replace it.

ChevyTruckLove75 said:

I wanted to ask one thing tho, I was doing a little research earlier and read somewhere about possibly the headlight switch itself could be faulty and causing an issue.,? I know that my light switch feels a little weird when I pull it to the first step (parking lights). sometimes I have to jiggle it to get it in the sweet spot otherwise the headlights turn on almost immediately.

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Usually it's the rheostat that fails most of the time just because the dimmer doesn't work at all or intermittently. Not a common piece to go bad, but it can happen and if it's feeling funky it's not a bad idea to swap it out.

Jgonick said:

My opinion is to go back to incandescent- at least until you get everything working correctly. LEDs add a few more layers of problems to figure out. First thing- make sure you have good & correct bulbs and the sockets look good. (Front turn signals are 1157, they a dual filament which is very important).


That is correct. The original side markers blink the same as the front signals with the headlights off. They alternate with front signals with the headlights on. With the headlights off- current goes through the (flasher) blue wire and grounds through the brown (through the dual filament front bulb)- they blink. With Headlights on- current goes through the brown wire and grounds through the blue wire (through the dual filament front bulb) for the parking lamps- however when you turn on the signal- it feeds current (flashing) down the blue wire- since current is coming from both direction (brown & blue wire) it causes the bulb to go out every time with the flashing current. Think of a garden hose with water coming from both direction- water will meet in the middle & not flow.

So when you add LEDs to that situation it gets confusing - LEDs only let current flow in one direction unless its been modified somehow.

Let us know what problems you are having with incandescent- if you go that route. Most light problems are usually cause by wrong/bad bulb or grounding issues.

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they make polarity insensitive 194, ive never used them but if they work good ill definitely be using them

ChevyTruckLove75 said:

amazing info guys!! thank you, I certainly have some ideas to look into ., first thing Im going to do is swap all the bulbs back to incandescent first and foremost!, then Im going to check that ground like a MF! and make sure the grounds are connected good!
I wanted to ask one thing tho, I was doing a little research earlier and read somewhere about possibly the headlight switch itself could be faulty and causing an issue.,? I know that my light switch feels a little weird when I pull it to the first step (parking lights). sometimes I have to jiggle it to get it in the sweet spot otherwise the headlights turn on almost immediately. I ordered a new switch anyways so I will try that but definitely after I remove all the LED's and replace the incandescent bulbs!

I'll keep ya's posted on the results!

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that sounds about right, if you do a relay harness you will extend the life of that switch immensely by making the failure liklihood only mechanical use not current burning the switch contacts etc

Definitely need your wiring to be working correctly and have proper grounds, to use LED bulbs without problems. We used them on my son's truck without issues because I corrected all the wiring issues before switching to LED's. One of the best ways to improve your wiring/electrical success is to switch from faith based electrical to verified. When you ask someone what the brown wire does, they will tell you what it's for. That does not take into consideration what has been done to the electrical since it left the factory.

Use a test light/meter to verify what the wire does and if it is still connected as it left the factory, verifying in the process the functionality of the individual wire and eliminating faith from the equation. FYI, the new generation of LED bulbs are not polarity sensitive. Also I have seen first hand on even newer vehicles (Jeep) that they are not consistent on which pin the factory uses for the ground on headlights. I did a simple headlight swap and the new LED lights didn't do the same thing when powered up, had to use a meter to figure out the factory had the grounds on two different pins. Re pinned the headlight connectors and everything worked great.

I just used LED on headlights and auxillary fog lights where it really matters and kept the rest incandescent. I have seen too many threads about issues LEDs in turn signals to even want to try it elsewhere