Interesting 12v issue

I am having a small issue. I bought some LED running/turn signal. Basically a HI/LO function. I strung a set of 7 lights together in parallel. The ground and LO (running lights) are all wired together. There are two sets of 3 lights wired separately from each other on the HI side for left and right turn signals. When the lights have power to the LO side, the turn signals work properly right and left light separately. When in day mode, running lights off (LO has no power) and you give power to the HI for either side, they all light up (will provide pictures with 2 lights as a small scale representation of what is happening).

I did some tests and figured that if either the LO or the HI are joined but have no power applied and power is applied to the other they all light up.

I know they are back feeding through the joined LO side. Why? Idk they shouldnt be.

My question is if I stick a diode on the LO side of each light will this solve my problem? If so what diode? (The ones that can be wired inline are highly preferred)

Picture explanation:
White is ground.
Black is LO
Red is HI

First pic ground and LO connected and 1 red HI connected to power (hard to capture on camera) but its lit and brighter then the other side.

Second pic. Ground and 1 red HI connected to power the LO are connected together but not to power, yet they both light up?


I think what you are experiencing is a circuit set-up in the light itself. Do you have a part number on the light?

Without a schematic my guess is that the circuit is set up on low to light the low LED and on High to light both LEDs in the one light. Because of this design there is power to both lines when in the High position. A simple continuity check would verify this behavior.

Once you have verified this you will likely need to run a separate power line to the left and right low sides with a diode on each line to prevent back feeding power to the opposite side.


In both situations that I’m planning on using these lights it would be impossible to run two completely separate power lines for the low they all have one power source a battery for my truck. The other being essentially a trailer with one wire for running lights. They would just back feed and cross at the terminal rather than by the light. But wouldnt an inline diode on every light stop the back feeding. (Also dont have access to my lights for aprox 12 hrs while at work)

Provided that this is the problem a diode on every low input would stop the power from getting to the other low LEDs on that line.

Is there a diode you would recommend? Like I said, I prefer inline style diodes

Assuming you are running 12v as you state you want to be a little higher as you are normally a bit over 14v. I would also assume that the LEDs are fairly low in current, however, maybe go with 1A to be safe. If the lights are available you may want to check current draw prior to use. Take a look at a part like 1655-1894-1-ND and see if that is what you are looking for?

It looks about right. Just to clarify what the spreadsheet was trying to tell me is that; in the direction its built to work it resists 700 mili volts. (Somthing like that) and prevents up to 40v at 1.1 amps from flowing backwards

Correct, so if you are supplying 12v to the diode it will drop 700mV and your LED will get roughly 11.3v. and on the reverse it will block up to 40v max so 12v should not be an issue.

Awesome thanks for the help, really appreciated it. Never had this issue before with led hi low configurations