TR2/3/3A Triumph TR3 Tail Light Issue when Headlights and Brakes are On

[sammy]

My wife has a "new to us" 1961 TR-3. During the day, her brake lights work perfectly fine. However, when the headlights are on and she presses on the brake, the left taillight goes out and the left brake light will not come on. However, the right taillight stays on and the right brake light comes on. When she releases the brake, everything goes back to "normal".

Once the weather warms up, I plan to look at it and hopefully get it fixed. I was hoping I could get some tips on where to look first from this group.

Thank you in advance for any information you can send my way.

 

[Jim_Stevens]

Hmmmm. Lucas Electrics! Download the free wiring diagrams for tr2-4 from www.advanceautowire.com, and start doing some checking/tracing. You’ll want to unscrew and remove the tail light covers too. It’s just a process of finding the short or miswiring. What happens to the front running lights during this? (Might be a clue) and you didn’t mention turn signals… all good there? By selectively removing some of the wires (they’re bullet connectors) you should be able to logically determine what’s happening.

 

[Jim_Stevens]

Come to think of it, might be time to shift to LED bulbs too… try > LiteZupp Industries, LLC <.

 

[bobhustead]

Almost certainly a ground issue.
Bob

 

[Jim_Stevens]

Could very well be, Bob!

 

[Mickey Richaud]

Another vote here for a ground issue.

 

[CJD]

+1

Any time you have strange happenings it is always a bad ground back feeding the bulbs.

 

[Sarastro]

I think it is almost certainly a bad connection somewhere. Might be a ground, might be something else. Those bullet connectors beloved of British car manufacturers are pretty awful, especially after 60 years. I'm not familiar with the way grounds are done in the TR3, but in the TR4 the bullet is inserted into a curly bit of metal that is screwed to the body. Any looseness or bit of corrosion and all kinds of strange stuff can happen. I'd suggest replacing those grounds with an eyelet screwed directly to the body. I like to solder the eyelet, but a crimp connection is OK if you are not into soldering. Go through all the connections and make sure they are clean and tight.

If that doesn't cure the problem, there is probably an error or unwise modification to the wiring. Never underestimate the abilities of a PO to do dastardly electrical deeds.

 

[Jim_Stevens]

Steve, agree w you. I crimp AND solder, but I’m an EE.

 

[CJD]

Yeah...I solder all connections too. The interesting thing is that the FAA forbids soldering wiring on planes, preferring to crimp. They say the solder puts a stresser on the wire that will eventually break it after a lot of vibration. I've never seen that happening on a car, though...I still solder there.

 

[Sarastro]

That's interesting about soldering on planes being verboten. As it happens, soldering is OK in space systems, but they get lots of vibration for a short time, then none at all. So, it's not the same.

I'm also an EE, been soldering stuff since I was 9 years old. Can't stop now!

 

[Jim_Stevens]

So I took a look at the schematic… the two (tail light and brake lights) circuits are completely separate, so as everyone said above, it must be a ground issue or a short at the double bulb socket. Sammy - let us know if you can’t read the schematic diagram. You’re going to be looking at the bullet connectors at each bulb, and looking for frays, wires being loose or touching. Start in the boot (trunk) along the rear skin, near the carpet. There are connectors there. then take off the red lenses and look there. There are automotive electrical specialists, but they bill out north of $100 an hour! Let us know!

 

[TRopic6]

+1 on the double filament bulb socket ground. The tail and brake light circuits are separate except where they are joined at the bulb ground. If the current for one of the filaments cannot conduct to ground, it will flow into the other 'cold' filament and through that circuit until it 'finds' a ground, probably in the other bulb...after flowing through the other cold filament. Although there is current flowing, its going through 3 filaments worth of cold resistance and the filaments will be very dim. This can happen to headlight too.
If you step on the brakes, the brake filament on the side with the ground will be 'hot' and the resistance much higher, and the taillight current will not flow. There is a thread somewhere that coveres this, but the bottom line is do like Sammy says - clean and check the ground for the bulb socket.

Jeff

 

[Jim_Stevens]

Oh good one Jeff!

 

[Graham H]

The first thing I would do is take the tail light lens covers off and retighten the tail light mounting screws and i think you will find the problem is solved, good luck.

Graham

 

[Andrew Mace]

The first thing I would do is take the tail light lens covers off and retighten the tail light mounting screws and i think you will find the problem is solved, good luck.

Graham

And if that doesn't work, oh-so-carefully clean the bulb contacts and sockets (maybe even the bulbs themselves) and the wiring connections to the lamp base plate.