72 c10 LEDS help with front parking and turn signals

[jonesmak1972]

TOO LONG DIDN"T READ : can I delete the entire front market circuit to eliminate it's ground requirement? Can I provide a ground for the front marker circuit by using a relay or is there a way to create a ground when no wire currently exists for it?....

Alright. I have posted here before about a similar problem but it is rearing its head again. I replaced the normal bumper on my 72 c10 with a roll pan and flush mount LED's.



The fairly obvious problem I have run into is that originally both the parking and the turn signal circuits used to ground through the housing in the bumper. As of now there is just an LED Module with a red power wire and a ground. I attached a 3 wire blinker module from CustomLED so that the single wire LED would function with park and turn signal. It also supplies a ground so I thought this would solve my problem but it hasn't.

My observations are as follows:

Lights in the marker position - no side markers (not right)
12v power at turn signal wire (not right)
12v power at front marker wire
both signals on on dash (not right)
Blinkers will blink, side markers don't

Lights in the off position - 0-0.5v at front marker wire
Blinking 12v at signal wire
both side markers blink

It looks to me that when the markers are on they ground out through the turn signals because I shouldn't have constant 12v at the signal wire. I'm to the point where I would gladly delete the front marker circuit all together if that would solve the problem but I'm not sure if this is possible. Does anyone know this?

Also I think if I could somehow use a relay to provide the ground for the front markers this might somehow solve the problem. Does anyone know how to do that?

Thanks for your help

[dmjlambert]

Are you using LED bulbs to fit in fixtures that will otherwise be able to hold a conventional bulb? Or using special light fixtures that have LED lights integrated into it?
If using fixtures that will hold conventional bulbs, I recommend putting the conventional bulbs in and verify everything works as expected, then consider changing to LED bulbs after you've done that.

[jonesmak1972]

Hey I appreciate the reply! There is no provision in the roll pan for the original light housings. These are pre cut for these specific LED housings.

Before the roll pan went on I confirmed everything worked perfectly with the old bumper.

I am considering cutting the brown Parking/Marker wire off the front 2 lights and splicing them to the brown wire on the side marker lights so that they get a ground and the side marker lights will still function but the fronts won't.

[dmjlambert]

To make a recommendation it would be good to know what you're working with.

So it sounds like for the parking lights/turn signal lights in front, they are LED and you do not have the ability to twist and remove the LED bulb and put into that socket a conventional bulb. It is LED only.

What about the side marker lights? Are those the type that you twist to remove the bulb holder and then pull out the 194 size LED bulb and can simply push into that bulb holder a conventional bulb and twist lock it into the housing?

[Dead Parrot]

On a normal OEM system, your thought that the side markers ground via the front turn bulbs is correct. It is kind of a sneaky but clever system. 12V to the side markers full time. They ground via the much larger filament in the front turn bulb and light when the turn bulb has 0V. When the turn blinker applies 12V to the turn bulb(same side of bulb the side marker is connect to), the front bulb lights and the side bulb goes out as it now has 12V on both sides. It is why the side bulbs blink out of phase with the front bulbs. This trick works well with incandescent bulbs but not with LEDs.

Simple solution is to wire the side markers to be on full time when the marker circuit is on but you will lose the blinking function. Ground the side that went to the front turn bulb and break the connection from the side to the front bulb. Not sure of the legality of this since blinking was part of the OEM setup.

You could add a second brighter LED to the side marker that blinks when the front LED blinks. You would wind up with Bright, dim, bright, dim vs the OEM dim, off, dim, off.

[Richard]

Dead Parrot is right on the money about the 72 markers. As he said you can add a direct ground for side markers to keep them on all the time with the running/parking light circuit. Same as 69-70. You could also add a N/C relay to the ground or power on both sides at the marker and wire the coil to the turn signal power if you want them to blink. Side markers will alternate as a stock 71-72 truck

[dmjlambert]

To achieve the exact OEM behavior of side marker lights on-off-on-off pattern that works with headlights on or off, and solid on with headlights on and no turn signal, you can make a full wave bridge rectifier out of 4 cheap general purpose diodes (like 1N4001) and install it on the 2 wires going to the LED bulb side marker light. Better than a relay.

Or if you can just use a conventional bulb in side marker since there is no real advantage of LED bulb in that position. If you're stuck with LED side marker because of the style of the side marker case you're using happens to have integrated LED bulbs, the bridge rectifier is the way to go.

Example of what I mean by cheap,
https://www.adafruit.com/product/755