Curious surface mount tailights

[Timber]

Not sure where to post a repair question, but we're newbies, so I'm guessing: here.

1997 Damon Class C on Ford E350 chassis.  Has surface mount turn/stop/reverse lights that look like Bargman #92 (but the lens colors look more like photos of Peterson lights).  Driver's side taillight a bit loose, so I popped off the lens cover, removed the bulb and tightened the two mounting screws.

After reassembling, the turn signal indicator flashed rapidly - like a bulb was burned out - however the bulb works, but it's very dim, and it's hard to see the brake light.  No spare bulbs, so I opened the passenger side taillight, popped out that bulb and put it into the driver's side and it made no difference.

Put the bulb back into the passenger's side and now it's acting as if the bulb is burned out, too, and although it works, that side is now very dim, too.

First thing today, I'm going out for new bulbs; that's for sure - but might there be another reason the lamps aren't working right?  Both were just fine until I fiddle-farted with them and the DB ("Dear Boss") is none to happy with me (and is threatening to make me sleep with the puppies...)

Thanks!

- Tinker

 

[BobNSam]

Possibility you bollixed up the ground for the light fixtures.
You may need to resort to multimeter to check for voltages and resistance path of the fixture to ground.
The metal shell the bulb mounts in should measure 0 ohms to ground, or very near, on the tow vehicle (you can measure to the ground connector on the umbilical).
Voltage should be measured at ~12VDC from each of the contacts to the metal shell of the light fixture when that light is turned on.
It would be a real coincidence if both bulbs went bad the same way at the same time...but life happens.
I have just replaced the light harness and lights on a utility trailer because I didn't carefully check for some of the same things.   
My $40 lesson was provided by a faulty tow vehicle light converter (should not be your problem).
Bob

 

[tvman44]

Sure sounds like a ground problem.

 

[Timber]

Possibility you bollixed up the ground for the light fixtures.
You may need to resort to multimeter to check for voltages and resistance path of the fixture to ground.
The metal shell the bulb mounts in should measure 0 ohms to ground, or very near, on the tow vehicle (you can measure to the ground connector on the umbilical)...

Thank you, Bob and tvman.  Hadn't replied because I'm trying to find where I hid my multimeter - the kids are famous for raiding my tool room - and maybe I hid it too well.

While searching, I did the easiest thing and replaced both taillight bulbs hoping that moving the right side bulb to the the driver's side (went bad first) might have damaged the bulb.  No joy.

When changing the bulbs I noticed a bit of oxidation on the bulbs and the sockets.  I don;t know how significant that might be.  I mention it because I did remove the driver's side lamp housing to re-caulk and surely could have buggered the ground, but all I did on the passenger's side was remove the bulb and - if that's all it took - I need to figure out what the heck else might be wrong back there.

Anyway... multimeter in hand, I'll probe the little devils this evening.  Appreciate the information.

 

[BobNSam]

Note that most trailer wiring harnesses only run one ground wire to the rear of the trailer where it gets "daisy chained" from one light to the other. If the connection/splice point is where the "disturbance" took place, it will affect both lights. You probably have only one problem where the ground wires join up. It could be in the first light you tightened up.
Again good luck.

 

[Timber]

Testing showed correct current and no continuity in the metal sockets.  But the problem seems to be caused by light oxidation in the sockets, themselves.  Carefully seating the bulbs took care of the problem for now, and both sides are working properly.  Will have to look at it more closely to come up with a permanent fix, but it was a fine "Duh!" moment for me.

I swear to all who offerred suggestions that I did this already - when I changed the bulbs.  Today it worked.  Who knows about tomorrow..?

Thanks, all.

 

[Mavarick]

This is pretty common in trailer sockets also. They work until you have to mess with the bulbs and once the "connection" is broken they never find a spot to reground themselves. Wrap some fine sandpaper around a pencil or whatever you can fit in there and rough up the socket so it will ground to the shell of the bulb. Scratch it up real good and it should work fine.

 

[Timber]

Thanks, Mavarick, I'll do this.

Adding this for anyone else with an odd-acting taillight: it was slightly (SLIGHTLY!) jiggling the bulb in the socket that got them working at full power again.  While oxidation is interfering with the ground, it's contributing to another problem, too.

When you insert the bulbs, you depress a "spring-loaded" disk with the contact points, then twist the bulbs into position and release the pressure on the disk that springs back to secure the bulb and the connection, and that disk did not immediately come back into proper alignment.

I'm not sure (too happy they were working) whether I managed to rotate the disk a hair when twisting the bulbs into position, or if the disk did not spring back perpendicular to the contacts on the bulbs, but interference with the movement of the socket's contacts also contributed.

It was a head scratcher, for sure.  It would have been easier on me if the lights had stopped working instead of suddenly giving off an extremely weak light.

Thanks to all who pitched in here.  After wandering around for two days muttering "WTH?" they're working and I can see the problem.

 

[WELDON]

For future reference, a little of the dielectric grease on all bulb ends,trailer harness plugs, will eliminate a lot of problems.  Boat trailer and pontoon for sure. You can get the handy little packets at hardware,auto parts store.  Always have 1 in the glove box of tow vehicle.
Kent

 

[Lou Schneider]

When the ground goes away, the two filaments in the stop/turn signal bulb are placed in series - thus the weak glow instead of going completely out.

The current path goes from the turn signal filament, through the common floating ground to the tail light filament, then via the tail light's hot wire to the hot side of the obstruction lights (they're on the same circuit as the tail light), then through the OB lights to ground.

 

[Timber]

When the ground goes away, the two filaments in the stop/turn signal bulb are placed in series - thus the weak glow instead of going completely out.

Thanks, Lou.  I was making the problem too complicated - just confirming what DB always says I do.  Wandering from a flasher unit fault, to a partial ground, to too much resistance in old wiring.  I'm sure you will save other newbies thousands of hours of just thinking about where to start searching for the source of the problem.

Weldon, the dielectric grease tip is excellent.  And another "Duh!" moment for me.  First motorhome, but I owned a boat for quite a while and used dielectric grease all the time.  Sometimes I'm shocked by how much I knew but just can't shake free of the cobwebs...

Earlier, Mavarick suggested that the taillight sockets need to be sanded to remove all the oxidation.  The best way to clean light to medium surface oxidation from electrical contact surfaces that I know about is to use a drafting eraser.  The white ones made by Staedtler do the best job, leave the surface polished, and carry away almost all fine debris.  Learned that one cleaning contacts in computers and it works just as good on lamp fixtures.

 

[SLJKansas]

One thing may have happened , that if the bulb has the two off-set tabs that set the bulb(when you put it in the socket and twist), is that you get the tabs in the wrong slot.  I have seen many brake/turn signal lights on when the lights are turned on one side is brighter than the other.  Done it myself, and didn't realize it until it waa dark.