New guy... LED issues

[cmomola]

Hi all! I just wanted to introduce myself and share a few photos... I bought my square body when I was 18 and she has stayed pretty much original. First pics are when I first got her around 2007. I've recently started taking off the old and preparing it for new. One of the main things I wanted to do was change over to LED lights. Everything works until I run the truck with the headlights on, then the rear tail lights blink once and stay solid. I've already swapped the relay, grounded it, and reversed polarity... Any suggestions?

 

[Moodyalaskan]

If the front only blinks once also, the LEDs are probably not drawing enough power to heat up the blinker relay enough to let it blink more. You will need a resistor to give the blinker relay enough to heat it up and continue blinking. The system thinks you have a turn signal out, and it will not continue flashing.

 

[cmomola]

The fronts are blinking fine along with the side markers. The rear are the only issue and only when the truck is running and the headlights are turned on. If the key is turned to Aux and the headlights are on, everything blinks fine.

 

[Broken85]

Put in a low amp blinker relay first and see what you have. This is an essential part of switching to LEDs. Don’t forget the hazards are a separate relay.

2Pin LED Flasher Relay with... https://www.amazon.com/dp/B0CNK6VM7X/

 

[Mr Clean]

 

[ali_c20]

Welcome from Austria.

 

[legopnuematic]

Welcome from Missouri.

 

[Sad Sack]

 

[jfrchevyguy]

Welcome from Kansas!

 

[animal]

 

[YakkoWarner]

LEDs can be fickle beasts, especially on these older machines that were built around incandescent expectations.

Slight current leaks or grounds with any resistance would be completely invisible with incandescent bulbs, but they can cause LEDs to come on because of how little current flow it actually takes to trigger an LED.

I'd make sure all of your grounds are really solidly clean, they can play all kinds of havoc by causing weird current flows if they are not. Only triggering on when the headlights come on with the engine running (but not with engine off) is a weird one. An outside chance is that your alternator rectifier is allowing some small trickle of A/C ripple to come thru along with the 14V DC charge, and that ripple is triggering the LEDs on half the waveform. It seems unlikely, but you're already looking at an unlikely problem. Are ALL the bulbs now switched to LEDs? If so you might try switching the fronts markers back to regular incandescents temporarily and seeing if your back lights issue goes away - they incandescents should absorb any small stray voltage/currents in the circuit.