A PO of this '48 made a custom surround for the speedo etc and he drilled it for LED indicator lights. I had to redo the wireing harnesses etc and now the LED highbeam indicator stays 'on'. I presumed i did something wrong and took everything back apart and finally got down to testing the headlight bulbs i see that voltage bleeds over from the lowbeam side to the highbeam side and it is enough to backfeed the LED highbeam indicator.
Have you guys run into this and what did you do to solve it.
Thanks, oj

 

That's usually a grounding problem.

 

You aren't cross wired with the connection to the socket, right? When I miss wired my setup, one of the high beam filaments was always on and the indicator was lit. Corrected the wiring (low to low/high to high) and the problem disappeared.

DW

 

No, i took it apart down to the bulb, all is as it should be. I can read across the bulb (12v halogen) and there is continuity from highbeam to lowbeam elements.
It seems that it bleeds some voltage back thru the highbeam circuit but there isn't enough current to light up an incandescent indicator lamp, but an LED dosn't need more than a few milliamps to light up.
I don't really know, just guessing.
Thanks, oj

 

There shouldn't be any "bleedover" through the high beam switch; are the contacts dirty or corroded ? Is there a high resistance short anywhere in the wiring to the light ? The LED would have to be wired parallel to the headlight circuit; are you using a relay for the headlights ?

Tom

 

There isn't any 'bleedover' in the wireing, it is in the headlight bulb, you unplug the bulb and the highbeam indicator works proper.
Nope, no relay. The actual wire to the indicator lamp come off the floor switch where it is on the same terminal as the highbeam wire.
I checked the bulb and you can read continuity between the '+' terminals for the high and lowbeam positive wires. I had an old 6v bulb laying about and tested it and you can read continuity between the high and low beams on it too.
Its almost as if i have to put a diode in the highbeam circuit to prevent the backfeed back to the diode.
If you have a bulb laying around check continuity on it, the pin on right is highbeam (i think), center is ground, left is lowbeam. These bulbs read continuity from left pin to right pin as if they share a common element.

 

X2 on the ground issue.

 

I say it's a grounding problem in your head light circuit .

 

I followed your suggestion right after you posted it and ran a seperate temp ground from the engine over to the terminal strip where the feed to the lights are and added it to the existing ground without any affect, with the lights 'on' i tapped the additional ground to the existing ground and the lights didn't change intensity. I thought they would but everything is new and the existing ground is part of the circuit (i run a ground along with the positive wires, just like your house). By tapping the new ground against the existing ground i expected to see the lights responding but they stayed at the same intensity. It is a good ground path with minimal resistance.
I agree with you, most electrical problems are grounds.

 

Have you tried other sealed beams to see if you get the same feed back from them out of the truck? Could this be a problem with all sealed beams? Ya may have to use a diode. Or duel headlights.

 

Where is the high beam indicator hot side connected, at the hi/lo switch or at the headlight bucket? Where is it grounded? I wonder if this has to do with reducing voltage to the LED for operation on 12v? Some have internal resistors, others need external circuitry and that may be causing the light to glow. Is it brighter when the hi beams are on?

 

"Its almost as if i have to put a diode in the highbeam circuit to prevent the backfeed back to the diode.
If you have a bulb laying around check continuity on it, the pin on right is highbeam (i think), center is ground, left is lowbeam. These bulbs read continuity from left pin to right pin as if they share a common element. "

The two elements for high and low will share the common point (ground) so measuring terminal to terminal you would pick up continuity ?

The high beam switch should be the isolation point between high and low beam operation, and the high beam indicator. Could you manually take the high beam switch out of the circuit; then jumper power to each (high / low) to see if the LED still lights ?<!-- / message -->

 

The current through the low beam filament will go to ground through the common connection between the low beam filament and the high beam filament. Once there it won't back up and energize the high beam filament to give you the spurious high-beam indication. Getting to ground is the goal of every electrical current.

Where does the other side of the LED connect?

 

By Joe!! I think you guys are on to it. Now just changing out the dimmer switch
Isn't going to help. Right?
The problem seems to be in the way the LED is grounded?
I thought current just passed through an LED to light it. Like a Christmas tree bulb.