TR6 Rear lights don't work. Grounding Problem ?

[Deleted member 19047]

So, after 15 years of mostly neglect, I finally retired and have time to spend on my baby. A 69 TR6 that I bought in 71. After new front calipers to get the brakes up to snuff, I checked out the lights; and to my surprise, they didn't all work. The front markers and headlights work, but the rears do not. Taillights, markers, or license plate light. The brake lights work, but so far the turn signals don't; and I assume they are on another circuit. But first things first. Looking at the schematic, the front lights work off the same fuse box connection as the rears, and the bulbs check out, and I have power to the socket. Logic points to a bad ground. There are what appears to be ground wires connecting to the back of the taillight housing by the turn signals, but is that all ? I roughed up the connections with some sandpaper, but didn't help. Any ideas out there ?

 

[TexasKnucklehead]

How odd, with only 15 years of neglect your Triumph has an electrical problem... usually they only have problems when used. -Oh, right, you tried to use it, That's the problem.

Congratulations on retiring. Welcome to the best on-line group in the galaxy, maybe even the universe.

Since you know you have power at the socket, you must have measured it, and had your meter connected to a valid ground. Somewhere you are losing it, but it seems odd to have all those things fail at the same time. Generally, Triumphs do not add a wire for the ground of the lights. They chose to use the housing of the bulb to be grounded to the frame via the screws that hold the housing to the body. Often the contacts inside the socket are not making good contact with the nubs on the bulb (perhaps the springs have perished). If you indeed have a failed ground, and know you have power at the bulb, you will measure the housing at the same voltage as the bulb (since if it was grounded, the light would work, but if the ground is open, it will show the power thru the bulb).

Since several bulbs are in the same housing, a missing ground will result in many bulbs not working. Since the front lights are working, you can assume the body is grounded -at least at the front of the car. Good luck and keep us posted with what you find.

 

[dklawson]

While it could indeed be the grounds, I suggest you remove the bulb holders from the lamp assembly and use a multimeter to confirm you have voltage at the sockets when the switch for the lamps is turned on.

 

[Deleted member 19047]

My initial findings of power to the rear was with a circuit tester probe. So this morning I followed up with a multimeter. I have 11.8 V coming out of the wire feeding the socket, and the same at the contact inside the socket, on both sides. Grounded the multimeter at the trunk latch. Then I took a wire brush to the 6 or so contacts on the outside of the socket, and a battery post brush to the inside of the socket. No change. I remove the left hand taillight housing. Then I put a jumper wire into the connector feeding the bulb and held it to the base of a bare bulb; and alligator clipped another wire to the body where the taillight mounts to the body, held the other end to the side of the bulb, and it lights. So the body at the back is definitely grounded. But still not getting the bulb in the socket to light. So I double check the right side. Pull the bulb, confirm power to the contacts, and put the bulb back in. I take the wire with alligator clip, ground to the trunk latch, clip the other end to one of the 6 retaining clips on the outside of the socket. Still nothing. Try a couple more and I get a flicker. Then I notice that I was getting a flicker because the I was touching the edge of the bulb itself at the edge of the socket. Hold the wire right TO the bulb side, and it goes ON ! Not only that, but the left side lights up too. Try it on the left side, and it works there too. From what I can tell, it looks like I need to replace the sockets. (Excuse me while I work this out here, as well as in my head). Sound about right ?

 

[Deleted member 19047]

Wait a minute ! The taillights use the same bulb as the stop lights, (and obviously the same ground) and the stop lights work !

 

[TexasKnucklehead]

Do you expect the stop AND the tail lights to work?

Don't make this more confusing than it is. The whole assembly of lights (Reverse, stop/tail, flasher and side marker) all use the same ground. Ground is "common" to them all once screwed to the body. Each bulb gets it's individual ground from the socket (the brass or aluminum colored base with the two protruding bits to insure correct orientation). The stop/tail light is a dual filament bulb. In order for both sides to function, both of the little solder blobs on the bottom of the bulb must get power from the associated wires supplying it, and ground from the shell of the bulb. If you look closely inside the socket at the bottom, you may notice a cardboard looking round thing holding the two contact points from touching. It also has a key such that rotating the bulb will not also rotate the two contacts. The key fits in a slot and is easily dislodged -giving way to intermittent contact with the bulb. The little spring under there could also be misaligned and not allowing both contacts to mate with the bulb.

Having good power and ground "near" the bulb isn't good enough. The bulb must be in perfect contact with all power sources and ground. You may find it easier to deal with, if you peel back the rubber housing a bit. The individual wires may be more moveable and you can figure where/when/how the connection fails. Once you find the issue with one of them, I'll guess the others will be much of the same.

Good luck, you are close.

 

[titanic]

If you haven't read this, it may be helpful-It is a common problem. https://www.buckeyetriumphs.org/technical/Electrical/TR6Sockets/TR6Sockets.htm
Another problem is the fuse box. The fuse holders are riveted to the terminals and corrosion can cause erratic contact. You can either replace the fusebox or clean the fuse holders and apply a drop of solder to the connection.
Berry

 

[TexasKnucklehead]

Oops, that article is probably more applicable. Sorry, I was thinking about TR3/4/4A sockets and forgot how different the TR6 sockets are. I apologize if I mislead anyone.

 

[Deleted member 19047]

I'm familiar with the dual filament bulbs in this configuration, but these aren't your typical bakelite and spring bottom sockets. They have what look like nylon sides with just a little copper tab about 1/16 in wide and 1/4 in or so long running down the side to make contact with the side of the bulb. It is connected to the outer rim with the 6 taps that snap in to the housing. The bottom has two fixed spring steel tabs that allow the bulb to rotate in place and make good contact. (I tried to load a picture, but things froze up). When I removed the bulbs and used the probe/multimeter, I would have power to the tab supplying power for the running lights,( and not the brake lights), on both sides. BUT, when I put a bulb in either of the sides, BOTH of the tabs in the bottom of the other socket would show power. AND, the housing that the bulbs snap in to is made of plastic. (The hole where the turn signal bulbs snaps in does have a metal flange around it, but I don't see where it connects anywhere else to something metal.) I don't think the chrome on the plastic housing is capable of providing a ground.
Just read titanics post as I finished this. (THANKS) Those are the sockets I have, and that is probably the problem. Still bewildered by the plastic housing thing, but since I can't find my soldering gun, I'll just order new sockets and see what happens.......

 

[dklawson]

I hesitate to suggest this but....

On our Spitfire we had problems with the rear lamp assemblies. Each bulb has its own snap-in socket which is supposed to make a ground connection with the lamp housing assembly through the socket springs. Ours gave problems for a while so I removed each socket and carefully cleaned each of rust. Then I used acid flux to tin a section of the socket and solder a 16 AWG black ground wire to each. You have to carefully choose the solder location so it won't interfere with the bulb and/or installing the socket in the lamp housing. Soldering was not easy and you have to wash off the acid flux when done. Regardless, in the end I had a whole bunch of black wire ends that I wire-nutted to a ground wire I attached to the tub. Our lamps have worked fine since then. However, I don't like messing with the rear lamps for fear of breaking those solder joints on the ground wires.

 

[bnw]

I never saw a more ridiculous excuse for a bulb socket then the ones on my TR6.

 

[TexasKnucklehead]

I never saw a more ridiculous excuse for a bulb socket then the ones on my TR6.

The TR6 trunk light socket... most ridiculous.

 

[titanic]

Sometimes I feel sorry for TR3-4 owners (as opposed to TR6s). Their cars are so simple and troublefree that maintaining them is much less of a challenge.
Berry

 

[Sarastro]

Don't forget that strange behavior is common with old bulbs. The connections inside the base can become intermittent, so they test OK but fail when inserted into the socket. Also, the tip contact of the base--that lead-like thingy--can oxidize and make poor contact to the socket. It wouldn't be a bad idea just to replace the old bulbs, if you are trying to create a reliable electrical system.

Also, to remove tarnish from the socket, try a wooden-pencil eraser. It will clean off the contacts without doing any damage.

 

[Deleted member 19047]

Got my new sockets from English Parts today. Problem Solved !!! Thanks to all for the suggestions.