67, 69 Barracuda and similar early reverse lights

[Mattax]

Maybe this will help someone in the future. It involved a little R&R, but what I mostly wanted to share was the electrical grounding issue.
The driver side reverse light on my '67 Barracuda wasn't working.

Connector was getting power, and bulb was old but functional.
Checking connectivity with the ohm meter revealed the socket wasn't in good electrical contact with the front of the housing. This was in spite of the fact that it was physically very secure.

Two sheet metal scews attach the lights attach to the body. This is what I first assumed would be the grounding problem, but it was not.

The socket assembly, lens and its gasket is attached to the chromed casting with two machine screws.

And even though this was rusty, cleaning that up didn't fix it either.

For touching up the black paint I used Testors enamel semigloss. Paint pen is easier but doesn't seem available in semi-gloss. The flat looked too flat.

 

[Mattax]

The meter was showing very poor connectivity between these to parts of the socket assembly.

If I had been willing to clip the wire in the middle, or remove the brass contact tip (they are available new), then I could have tried brazing or welding.
Those probably would provide the best connection. But I didn't think about splicing the wire 'till later and don't think I ever bought those brass contacts.
First thing was to clean around the joint with wire brush and emery cloth. Followed that with a mini-wire wheel in a Dremel.

To get deeper in, I applied naval jelly with a toothpick. Let it sit for a half hour, then rined, dried, rinsed again hot water and dried again. Muriatic acid probably would have worked as well.

I happen to have a couple of big old soldering irons. Not real big 300 Watt irons but big enough for this.
The butane powered torch didn't have enough heat on its own, and obviously I didn't want to use a larger open flame with the wire still in the assembly.

Resistance is now down to a fractions of an ohm. Later today we'll see if that does the trick.

 

[Murray]

I have seen this problem before- this is all part of the ground path. Good repair.

 

[4spdragtop]

Thanks for posting Matt! Great idea I'm going to try....someday lol

 

[Dana67Dart]

Don't think you will have any issues with it now.

 

[Mattax]

You're a winner Dana!
A little touch up before installing including some waxy rust preventitives and aluminum spray paint.

 

[4spdragtop]

 

[Mattax]

An interesting couple of side notes on the bulbs.
The factory specified bulb is a 1073.
Often 1156 is used as a replacement.
Specifications for both are the same (as far as I can tell) except for two; rated life, and current draw.
1073 bulb is rated for 200 hours, and 1.8 amps
1156 bulb is rated for 1200 hours, and 2.1 amps.

So at first glance it seems there is no reason to stick with the 1073.
The 1156 produces the same light (402 lumens) and should last longer (assuming the quality is the same - big assumption these days!)

But this is not quite the one to one comparison it seems to be.
It would only be true if there was no resistance in the circuit. Unfortunately, there is a lot of resistance in this circuit, at least on my car.
With key in accessory, right lamp powered, there was 12.2 V across the battery and 11.5 Volts between the left lamp connector and ground.
Between the battery positive and the bulkhead terminal after the reverse switch there was a 0.5 Volt drop.
The reverse switch on my car is now in the transmission rather than the column. This adds a considerable distance to the wiring and arguebly smaller contacts at the connection and in the switch than the column mounted version. The connecting harness is new from M&H and at least visually looked as good as my homemade one.

Regardless, the point is that its a long distance for 18 ga automotive wire and with a fair number of connections.
A lamp that uses less current will have less voltage drop through a given resistance than one that draws more current.
The end result will be the lamp using less current will see higher voltage and therefore be brighter.
Interesting, huh?
Maybe one day I'll test this with a light meter. That day being the next time I have to change a bulb...

For ballpark estimate of the resistance from the voltage drop we can use the rated current draw of 1.8 amps at 12.8 Volts.
change V / I = R
(12.2 V - 11.5 V) / 1.8 amps = R
0.7 V/1.8 amps = 0.39 ohms

Therefore with two 1073 lamps
I x R = V
3.2 amps x .39 = 1.2 Volt drop

and with two 1156 lamps
4.2 amps x .39 = 1.6 Volt drop

We know with lamps that lower voltage can have a noticible effect on lighting. For example as shown here for headlights -> Daniel Stern Lighting Consultancy and Supply

Whther .4 Volts lower with the 1156 vs. 1073 is enough to cause noticable (not just theoretical) less illumination I don't know. But it makes me feel better to keep using the 1073 while I've got 'em.

And no, I'm not worried about 200 vs 1200 hour lifespan. That's a lot of time driving in reverse, and I can still change lightbulbs by myself (and without looking for a you tube video).

 

[Mattax]

Here's the long and winding path in my car and would be similar in a '69.
On a typical '67 with automatic, the reverse light switch is on the column or floor selector.

 

[Dana67Dart]

Carefully with the " brighter" bulbs I melted a lense once (non mopar) they tend to get hotter.

 

[Mattax]

Carefully with the " brighter" bulbs I melted a lense once (non mopar) they tend to get hotter.

True on a plastic lens location!
And it also means more current load on the wiring.
Thing is on these reverse lights, the 1156 and 1073 are both supposed to provide 402 lumens at the rated voltage. So the trade off seems to be longer life in exchange for more load on the wiring and possibly dimmer lighting.

 

[Dana67Dart]

Same luminance, shorter life, how many seconds in a year are you in reverse?

I removed an original turn signal light bulb out of my 318,000 mile dart.

Probably the reverse light would last you 20 years?

I vote for lower amps

 

[Mattax]

Funny. I was wondering if the bulb was original. If so its been through alot! At least 250,000 miles, 50 years - 30 in the Northeast, and two rear end accidents.

 

[Dana67Dart]

Who is the manufacturer?

My turn signal was painted yellow and GE (IIRC) I had to brake it to get it out. Didn't want to but the bulb glue was gone.

 

[Mattax]

Who is the manufacturer?

My turn signal was painted yellow and GE (IIRC) I had to brake it to get it out. Didn't want to but the bulb glue was gone.

Maybe Westinghouse ? Found a photo of the other one - might be same.

My front turn signals are painted yellow, not sure if I wrote down the manufacture. I know I've replaced at least one. Bought a box of painted yellow Sylvania ones from Stern when he was into old stuff. Send me in a PM if you want a couple.

Found a pic from when I changed one this past year or two. GE on left. New old stock Sylvania 1034A on the right.

 

[RedFish]

Just FYI... This same lost ground connection where the socket is crimped to the fixture is more common in the front park/turn fixtures of a 67 model. The socket is similar tin part but the fixture is cast pot metal. Great big gobs of solder around this crimp joint wont fix the front fixture long term. Solder a ground jumper to the exterior of sockets works. Drill a hole through the crimp joint for a tiny screw works too but the screws head should not contact the glass globe of the bulb.