Hi Folks,

The tail lights on my 56 are pretty rusted due to salt/rock spray from the rear tires during previous ownership.

I bought some new tail lights from Mid 50's. See pic.


However, the new tail lights have two wires, my existing ones have three, the third being grounded to the frame near the back bumper.

The (conveniently) labled Ron Francis harness has 4 wires leading back to the tail lights. Right Tail, Left Tail, Right Brake and Left Brake. I think the brake light is turned on intermitently for turn signal functionality.

The bulbs in the new tail lights have two filaments. I presume one for tail lights and one for brake lights. But playing around with the new tail lights and my 12V battery, I can only get one of the filaments to light up, and that is with one wire connected to the pos. battery post (12V) and the second to wire to the neg. battery post (ground) on the battery posts.

I would think that the filaments should be grounded through the metal body of the tail light, back to the chassis ground, and that running one wire to 12V hot would light up one filament (tail light), whilst running the second wire to 12V hot would light up the second filament (brake light). But it does not seem to work that way so I am a bit confused.

Can anyone assist?

Thanks,

Gustave

 

Gustave, This unit is more than likely ground thru the mounting bolts. There is probably a grd wire from the socket to the bolts inside the housing. One wire is taillight and one is brake/turn signal. Run a jumper from one of the bolts to the negative of your battery and then check both (one at a time) to the Positive and you should have both functions.
Vern

 

That is along the lines I was thinking. Just I figured that the mounting bolts would be grounded to the housing, so I simply touched the housing to the neg. battery post.

Let me try it with a jumper to the mounting bolt directly and report back.

Thanks,

Gustave

 

I have the same lights in ss, I ran a wire from one of the screws to the body on each in order to get a good ground that would allow both the brakes & signal lights to function correctly. Also if brake/signal lights aren't working check to ensure the two contacts inside the socket are aligned with the light contacts, I had new ones that weren't so I had to modify one side so it would line-up correctly.

 

HI Gustave,

You are correct. The tail lights you have should be grounded through the frame. One lead should power the running lights and th eother should power the brake light.

If you have turn signals installed, that utilizes the brake light filliment to flash on and off. The four wires you cable has running to the back will be: Running lights (hooks to both sides - usually brown on generic cables) left brake/left signal (usually yellow on generic cables); right brake/right signal (usually green on generic cables); and possibly a white. The white can be used for a dedicated ground (especially on trailer lights) or back up light if you are so equiped.

Try this. Try hooking up a jumper wire to one of the mounting studs to the ground of the battery. Then touch each wire lead to see if it lights up. If it does, then try touching one lead and clamping it on, then touch the other lead Both work? OK! Now touch one lead then both leads at the same time. Did it get brighter when you touched the second lead? If it did then what has probably happened is you have a bulb where both filliments produce equal lumnes (same brightness) and the brighter brake/flasher is produced when both turn on at the same time - it may be hard to tell.

That's a little unusual. Normally with a generic bulb (GE1176) one filliment is brighter.

A redundant ground wire from the mounting stud to the frame as Jaye suggested is not completely necessary, but is a good idea to ensure adequate grounding - especially later on down the road.

 

A VOM or a simple continuity tester should tell you the story. first check the bulb to be sure it is a double filament bulb (typically a # 1157) it should have two filaments inside. Remove the bulb and look for two contacts on the bottom of the bulb. Look into the socket and there should be two contacts in there. The socket should also have on deep and one shallow slot for the pins on the side of the bulb. Put power to the bulb or use the meter/tester to verify both filaments work (bulb filaments are often broken in shipment).
Next use the meter/tester to check that one wire goes to each contact in the socket and the wires are not disconnected/broken. Check that the outside of the socket and the housing mounting bolts are continuous. (note that the outside of the housing is painted, so touching the painted housing with the battery/meter/tester will not ground the unit.) If all of this checks out it is all working properly. The green wire should be the turn signal filament wire, the black the taillight.

 

Wow. Thanks Vern, Jaye, Julie and AX, for the advice.

Sounds like my theory on how the lights should work is correct. I just did not test it properly. I'll try and do a more thorough job of it tonight.

Gustave

 

Oye! Never thought about suggesting you test it with the meter - da doy. The Holidays are killing me!

 

Yes. I did that this evening. The problem was that the paint on the new tail light housing was preventing the bulb base from making a good contact to ground-out to the metal socket.

My bulbs do show a higher resistance on one filament than the other (1.0 Ohms vs. 2.3 Ohms). So it looks like the brake light filament will burn brighter than the tail light.

I'm thinking of trapping a bare wire between the bulb base and the socket, and running that to chassis ground. Sort of brute, but it would sure guarantee a good ground path!

More likely I'll just scrape/sand the paint off in the contact area.

Gustave

 

That would be best, along with a dab of dielectric grease to keep rust at bay.

 

Yes indeed - one of the reasons for the suggestion on the redundant wire and the "Second" on that motion. Later on down the line dirt and rust will impede that ground just like the paint did this time - which is what I was trying to elude to above.

I'll bet AX is laughing at me over the meter thing. I'm a big meter person, but just "spazzed" this time. I'm so embarressed!

 

Gus, Julie suggested checking bulb base to the mount bolts. Then you said "trapping a wire between the bulb and the bulb base". Don't do this. There should be a third wire out of the tail- light housing or a wire from the bulb base to the mount bolts. If not, is this a factory defect or a bad solder joint? If needed, solder a new wire to the outside of the bulb base and attach the other end to the mount bolts on the inside of the housing. A suggestion. Unless I'm reading this wrong. chuck

 

These tail lights do not have any third wire. What you explain is one of the things I've thought about doing. Basically, you want a solid reliable electrical path from the base of the bulb to the chassis. There are a number of ways, I suppose, that this can be accomplished. I'll see what I end up doing and report back later.

Thanks folks,

Gustave

 

Is there enough room thru the grommet to bring out another wire? If so then I would solder a wire to the side of the bulb socket and bring it out so it can be mechanically grounded. If not the sanding of the inside of the housing would work. The lens should have a gasket sealing the housing, rust would be very slow to form, a screw into the chassis for a wired ground would be much more exposed to rust formation.
Julie, I would never laugh at you.

 

Thanks AX....It's the Holiday season and the weather for flying is Horrible - I've been snowed in three times in the last two weeks so I'm a little "slap happy"

As far as room for wires, sure there is.

If you want to run a "safety ground" I'd just simply solder a long wire onto the side of the socket where it won't interfere with anything and squeeze it out the rubber grommet then run it to the frame. Be sure you clean the frame and anchore it with a solid screw.

Again, if all your contacts points from light housing to bracket, to stake pocket, to frame, are good solid clean metal, then the redundant ground wire isn't necessary.

I don't have/use one, and I have NO problems. But I'm sure of the connectivity between those parts.