Tail light mod (both lights used as brake and signals)?

Ok. So post #210. 9 Ohm resistor. I’ll give it a try! Thx!

 

This looks good but at the end where the brake is on and signaling the new config on the left goes dark as it signals...I'm assuming the headlights are on.

 

Have all my parts and should get to it this weekend. I orders 8 ohm resistors so that should work.

 

Doesn't look like the headlights are on as the tail lights are not illuminated. But I believe it still is the same behavior when the taillights are on, I'm not sure though. But that's exactly how a bunch of the Ford pickups are done.

 

8Ohm seems to be easier to find and may also work. I just used what I had.

 

Just to troubleshoot, anybody know what would happen if I put two 6 Ohm resistors in series??

 

Then you would have 12 Ohms of resistance. At some point I guess a fuse might blow, but don't know at what point that would be.

 

Sorry, I guess my Apple emojis don’t work on TW.

Thanks @mesojdm I’m a visual learner... that well ingrained in my head!

 

The point of the resistors is to trick the bulb failure detection circuitry into thinking the power efficient LEDs are power hungry incandescent bulbs. So why aren't you putting resistors on the LED brake bulb as well since that's being used as a turn signal, right?

 

It's all wired together with the DD module. So you only need it on the turn signal wire since that is the one that will be powering both of the lights.

 

Maybe that's the problem then. The turn signal circuit sees a load when the blinker is on and then when you add brakes the turn signal wire sees even more load.

How much work is it to just disable the bulb failure detection logic? In a Benz you just disable it with the dealer tool.

 

Well that's the counter intuitive thing. I figured since it would see more load, you wouldn't need as much resistance. In my case though, I had to add more resistance. It's strange.

AFAIK you cannot turn off the bulb failure logic.

 

More resistance is less load. A bare wire is near 0 ohms and will get very hot and draw current until the fuse pops.

 

Well that doesn't make sense to me lol. If more resistance is less load, and the LED's already have less load since they don't draw as much as the halogens, then we are telling the computer we have even less load than LED's to trick it into thinking that the bulb is on??

 

No. You are presenting the load of the resistor plus the load of the LED to the truck. So it's more than just LEDs alone. A lot more. That's why the resistors get hot. It's wasted energy.

 

But you just said more resistance is less load.

 

It is. if the resistor had a value of infinity it would be the same as an open circuit. No current could pass through it = Less load.
If the resistor has a small value it will lets lots of current through it = More load.

 

But then you said I'm presenting the load of the resistors + LED to the truck. And I'm wondering why I needed more resistance to end my hyperflash issues when running two LED bulbs vs. one LED bulb.

So in my case, I had hyperflash with no resistors and LED bulb. I assume this is because there is less current going through to power the LED bulb. So you add the resistor and more current will go through there to increase the overall load on that circuit and not trip the hyperflash detection.

When I added the DD module, it was now running two LED bulbs but would not work at all with the truck on and the single resistor. The additional LED should have added more current right?

I removed the resistor and it worked with the truck on, but hyperflashed if I hit the brakes or the lights were on.

I had to add an additional resistor so that it would work with the truck on and brakes or lights on.

This doesn't make sense to me as why would it work better without any resistor, but with just a 6Ohm resistor it wouldn't work at all with the truck on? The signals wouldn't come on at all. Sometimes they would but they would flash a couple times and then stop.

I'm not an electrician so I'm just trying to make logical sense of the results.