Need help solving a wiring problem...

Hi, I'm new here; hoping someone can help me with a problem I have &, over time, maybe I can help others.

I've attached a diagram for the headlight circuit on a car I built.  The headlights work, but I've not been successful adding an LED to indicate whether they are in low beam or high beam and need to get that working.

I have an RGB, common cathode LED and have wired it as shown in the picture.  It may be obvious to some of you with more electrical experience than me, but but instead of off; green for low beam; blue for high beam -- I'm getting off; green when I turn the headlights on; both green & blue when I flip to high beams; stays both green & blue when I flip back to low beams; goes off if I turn the headlights off.

The one thing I found while trying to trouble shoot that I wasn't expecting is that the wires connected to the 87 pins on relays 2 & 3 show +12V.  That makes sense given the lights simply have a coil between the + & - sides but I wasn't expecting that -- not sure if I'm backfeeding 12V to ground [which might explain a couple of gremlins I've been chasing in other parts of my wiring system].

So, net, I have two questions:

1.  Is there anything wrong with the headlight circuit the way it is set up in the diagram?

2.  Why wouldn't the LED be lighting as expected vs. what I'm getting per above?

Note - I didn't draw in the resistors required for the LEDs to work with 12V power, but I do have them on the LED.  Both the blue & green sides do light properly when I connect them directly to the battery to test.

I appreciate any help you can offer!

Thanks in advance.

Picture of Need help solving a wiring problem...

Why are you going through all the trouble to try and switch a relay for the LED indicator? Why not simplify the setup. First of all do you plan to have your dash lights on all the time? Typically the dash lights come on when you turn on the headlights. Making the dash lights the indicator. Keeps things much simpler since you can wire the dash light to the headlight switch. Then the high beams will have there own separate indicator light tied directly to the switch.

CustomV8MGB (author)  mpilchfamily3 years ago

Thanks for taking the time to help out!

Not sure I'm following you though. The car's wiring, with the exception of the LED indicator for low beam vs high beam was completed several years ago and it works fine - including the dash lights which are regular bulbs in the gauges and a few illuminated switches. The dash lights are represented on the diagram I posted above and they only come on when the headlights are on as you would expect. I am now simply trying to add the LED indicator for high beam which is required for me to pass inspection. Since I had to pull the dash, I decided to use a bi-color LED to light up green when the headlights are on and switch to blue when the high beams are on. The green is simply because I am so used to automatic headlights on my daily driver that I keep forgetting to turn them off on this car. The green light on the dash should help me remember.

You are right that I do not need the relay for the green low beam because I can pick up power from the dash lights wire already there. But what about the high beam indicator? How would you recommend I wire that given a) how my lights are currently wired and b) recognizing the LED is a common cathode bi-color LED so green and blue need to share a common ground?

If all you need is a high beam indicator than only use a single LED on the high beam switch. Just wire the LED and resistor in parallel with the switch for the high beams. Nothing to it.

CustomV8MGB (author)  mpilchfamily3 years ago

All I need is the high beam indicator, but I want both the green low beam indicator and the blue high beam indicator in the one spot on my dash - hence the bi-color LED. My issue is it doesn't work if I simply wire the anode to constant power and the cathode side to to the high beam trigger. I think it's because the way the headlight relays are currently wired, I think it is back feeding 12v on the negative trigger wires.