High beam indicator always on?

Every car has an electrical system. Here's the place to learn all about it.

Moderator: 2088 bob

Post Reply
cdm
Posts: 7
Joined: Fri Aug 26, 2016 6:41 am

High beam indicator always on?

Post by cdm » Sun Oct 01, 2017 4:26 pm

Working on a Manx I recently acquired. Headlight wiring seemed OK (no relays). Hi and low work fine. However, I discovered when I connected a high beam indicator (led) it is on all the time. With the lamps removed the ground and voltages check out at the sockets showing 12v at the connection corresponding to the dimmer switch position and no voltage at the supposed open side. But, when I plug a lamp into either socket I get 12v on both sides regardless of dimmer switch. The lamps are old style 7" sealed beams. I put the ohm meter on the lamps and see there is continuity at all three connections all the time. Is this correct?

Can anyone suggest what I might be doing wrong here? It's only a half dozen wires and some fuses but I'm whipped...

User avatar
Dale M.
Posts: 1602
Joined: Mon Oct 05, 2009 10:09 am
Location: Just a Little Bit West Of Yosemite Valley

Re: High beam indicator always on?

Post by Dale M. » Mon Oct 02, 2017 10:10 am

LED should only be on when high beam voltage is present.... LEDS are also polarity sensitive, you may have it wired backwards and it is backfeeding a voltage from somewhere else and hunting a ground through head light filaments...

ALSO check to be sure wiring of headlights is correct, you could have one hi/low reversed and it could be causing problem...

Note how high beam indicator is wired (concept - same with switch as relay) in graphic... Should be same for LED or incandescent bulb...
Image

On headlamp internal construction one terminal is GROUND (common to both filaments) one is for high beam one is for low beam... Colors shown on graphic are what "some" after market sockets come with...Yours may be different... But it's all about position...

Image

Dale
Lives his life vicariously through his own self.
1970 "Kellison Sand Piper Roadster"

cdm
Posts: 7
Joined: Fri Aug 26, 2016 6:41 am

Re: High beam indicator always on?

Post by cdm » Mon Oct 02, 2017 9:10 pm

Thanks Dale. I did recheck the wiring against your diagram (thanks) and it is correct. The mystery to me is that both of the old sealed beam lamps show zero ohms between all three contacts. When one lamp is plugged in the other socket will show 12v no matter where the dimmer is set. When both are plugged in they do seem to work and do respond to the dimmer but with the dimmer in the dim mode there is 6v on the bright terminal; enough to drive the led. Interestingly I had a brand new set of modern halogen bulb type headlights in the collection (H4 bulbs) so for grins I rewired the sockets for this type of lamp and voila, all the 'ghost' voltages disappear and everything works as it should.

I was down to my last hair on this issue so I will use the modern lamps which is OK for a Manx. Thanks very much for the input and the diagrams.

User avatar
Marc
Moderator
Posts: 23723
Joined: Thu May 23, 2002 2:01 am
Contact:

Re: High beam indicator always on?

Post by Marc » Sat Oct 07, 2017 8:59 pm

cdm wrote:
Mon Oct 02, 2017 9:10 pm
...When both are plugged in they do seem to work and do respond to the dimmer but with the dimmer in the dim mode there is 6v on the bright terminal; enough to drive the led...
If the headlamps are in fact wired correctly the only explanation for that would be power coming through the dim filament and backfeeding through the bright filament because the ground is faulty - both filaments have a common point at the ground lug but if there's no ground they're effectively in series.

To be sure you aren't getting interraction between the two headlamps and their wiring, connect them one at a time.

I'd check those plug connections one more time. Dale's diagram shows the bulb as seen from the back side, NOT the pinout of the plug (which'd be a mirror image).

Post Reply