leds aren't lighting up, stumped

I have to ask; is a car battery charger wildly different than a car battery when used as a power supply?

here's the issue as simply as I can put it: I wired up some  strobe LED's to be used as turn signals along with resistors. When I tested my system out on my desk using a car battery charger as a power supply everything worked perfectly. As soon as I wired it up on my vehicle, the LED's won't  light up. If I look closely I can see a little bit of light, I mean i'm putting the led 2 inches from my eyes and I see something. When I connect the LED's to the car battery charger, they are extremely bright and blinding.

I went so far as to connect the LED's wires directly to the car battery, same result. Everything electrical on the vehicle works perfectly.

My multimeter shows 12 volts on the battery , and 13-14 volts with the vehicle running. Battery charger shows around 10 volts on the 10 amp setting

My battery is a lifeline agm battery

vehicle is a chevy express 3500

Any ideas?

polarity is definitely correct

I am using resistors to limit current

Led's light up everytime when using a car charger

I tried connecting the led directly to the car battery of my wife's car, same result, won't light up properly

Thank you Oldspark, yes I made the mistake of designing the system by trial and error. After reading your response I used a adjustable power supply until the LED's lit up, 18V made them light up. I'll never use a car battery charger again :(

thanks again, i'm sure the ripple you're talking about was making my LED's light up.. back to the drawing board for me. part of the problem is I have no specs on the LEDs (ecco 3510a led strobe) I assumed 12v would do the trick, the inline control module must be doing something completely different than what I thought.

I have 6 of these in various locations, two that are on either side of the box at about the center I was wanting to use as turn signals as well.

like you said, the control module didn't like PWM at all (fisrt thing I tried) , so I attacked the led array by itself with 7 diodes; the pcb has 4 wires coming out of it, I followed the traces and found out that one wire is (+) and the other three are (-).  I soldered the diodes in line so that the (+) and three (-) would only flow from the control module to the LEDs. I then tapped the positive wire on the LED side of the diode, and tapped all three (-)s on the LED side of the diodes and joined them together to run a single ground wire to my relay set.

Four SPDT relays connect and disconnect ground from the control module and connect PWM ground directly to the LEDs... these relays are activated by the headlights (+).

Two positives are then wired to the LEDs, first positive is coming from the turn signals, second positive is coming from a different relay that's controlled by a switch activating all emergency lighting; this one goes directly to the control module.

The LEDs are square, i'm assuming high current type. I'm also assuming the control module needs to control the 3 lines of LEDs individually for strobe purposes, but I could be wrong.

Unfortunately the control module is encased with melted rubber, even if I can melt the rubber off to see what's in there, the components will be desoldered as well i'm sure :( 

Thanks Oldspark :) 529 is fine

Sorry for multiple posts, i'm a bit on the slow side.  I wanted to ask if you recommend implementing a voltage regulator to future 12v automotive projects to avoid surprises like this one?