High Beam Indicator Always On

[Deleted member 7471]

On my TR4-A, when the headlamps are turned on, the High Beam indicator lamp is on always, regardless of the position of the dimmer switch. When the headlights are on low beam the indicator glows a little bit dim. When the switch is made to high beam, the indicator glows somewhat brighter. I haven't checked, but I assume both elements in the headlamps are always on also.
My guess is that there is a short somewhere in the harness where the dimmer switch supply wire (Blue) is making contact with the high beam indicator wire (Blue/White). I checked the operation of the dimmer switch with a VOM, and it seems to be working correctly.
Am I on the right track here or is there something I have overlooked?
Thanks for any opinions.
Glenn

 

[Geo Hahn]

This will happen if you have a bad ground (Bad Ground, Bad!) on the headlights. This is a black wire somewhere just behind the light bucket that plugs into a receptor for a bullet connector.

What happens is that the light can't 'find' it's usual ground so it runs back thru the high beam circuit, thru the indicator light (which then glows dimly) and finds its ground.

Okay, that's not how an EE would explain it but it works for me who thinks of electrics as a sort of plumbing.

 

[14dna]

Check to make sure the headlights are grounded properly, as it sounds to me like their back feeding the system to get a ground. This will also show as both filaments are on all the time.
Dave

 

[Deleted member 7471]

The ground seems to be good on the headlights. I checked and cleaned the gound points for the front end wiring. Also, I can remove the high beam indicator fixture from the dash and the headlights work fine. Makes me think still there may be a short, but I am certainly no expert in this type troubleshooting.
Glenn

 

[Deleted member 7471]

After a grand tour of the Lucas electrical system, I got to the source of the problem. The high and low beam wires on the right headlamp had been swapped (PO issue) - the poor thing was cross-eyed! . I understand that there is a plug that should house the wire connectors and prevent this problem, but this car did not come with that option - the wires just plug into the lugs on the headlamp. The car is a recent purchase, had not driven at night and I was doing my troubleshooting in bright daylight, so the problem was not immediately obvious.

One good thing - in the process of troubleshooting this problem I was side tracked enough times to diagnose and repair every electrical problem in the car, and there were lots - some I didn't even know about. Another good thing - next time there's an electrical problem, I'll know how to fix it, hopefully without spending 2 weeks.

So now I will drive in electrically correct luxury - til the next ground goes south....

Glenn

 

[DNK]

You can pick up that plug and the correct terminals at most auto parts store. the terminals are usually called GM style.

 

[Andrew Mace]

...I understand that there is a plug that should house the wire connectors and prevent this problem, but this car did not come with that option - the wires just plug into the lugs on the headlamp....

Glenn, what do you know of the history of the car? i.e., was it originally delivered in the US? (I'm thinking that possibly the car could originally have been equipped with different headlights and, therefore, different connectors.) Also, are both headlights missing the plug? Seems odd to me, but one never knows all that might happen to a car over a 40-year period! /bcforum/images/%%GRAEMLIN_URL%%/crazyeyes.gif

 

[MGTF1250Dave]

Aloha Glenn,

If you decide you want to install head lamp plugs, here is a source:

https://www.britishwiring.com/Comp.htm

They offer either the plugs alone or a complete headlamp pigtail with the plug.

 

[Deleted member 7471]

Andrew
I have a pretty good history of the car - bought from the original owner. The car was picked up at the factory in Coventry, so no - not originally delivered to the US, although purchased through a US dealer. The headlamps and connectors are both the same - appear to be original equipment, Lucas, not sealed beam, both missing the plug(but I am certainly no authority on this stuff). I will say that the original owner took meticulous care with the car and I would not think he would discard the plugs, but you never know.
Glenn

 

[Deleted member 7471]

Thanks for that link Dave - good source for electrical. For that price I think I will add the plugs. Might prevent days of troubleshooting for someone (me?) in the future.
Glenn