The Stovebolt Site Forums The Shop Area The Electrical Bay Tail light ground?

I've been having some problems with the rear tail light on my 54 1/2 ton. It seems that the bulb socket is not grounded, and I can't tell how this is supposed to happen. The wiring diagram shows a ground at the tail lamp, but my tail lamp only has two wires coming off it, one for the stop light and one for the tail light. Shouldn't there be a third wire for the ground, or is the grounding supposed to happen through the lamp housing?

Also, the PO had spliced into the tail light wiring to add a license plate light, and what appears to be a wire for a trailer. The connections were all twisted together (no solder), and looked very ragged. I just cut it all out so I could start fresh.

So what I have now is two wires coming from the front of the truck (as it should), and I've verified 6V on one wire when the brake pedal is depressed, and 6V on the other wire when the park and headlights are turned on. So I think the wiring from the cab is good and intact.

So you'd think you just connect the two wires from the lamp to the two wires from the truck, right? Well, that doesn't work. I tested the bulb I have, and here is what happens:

1) 6V to bulb filament #1, ground to bulb housing = filament #1 lights up.

2) 6V to bulb filament #2, ground to bulb housing = filament #2 (brighter) lights up

3) 6V to bulb filament #1, ground to filament #2 (or vice versa) = filament #1 lights up.


So, based on my tests, the reason why my tail and stop lamp aren't working as they should is because the bulb housing is not grounded. If it were, then the two filaments would work properly. The way it was connected before, only filament #2 would light up. And it would only light up when the brake was pressed and the park/headlights were off!

So, I'd really like to know how the tail lamp is supposed to be grounded!! This should solve my problems! Thanks.

Greg,

Your assumption is correct on the grounding. The brass lamp housing is swaged into the assembly. This should be a perfect ground from housing to taillight assembly. The taillight assembly is then bolted to the bed. This connection must be clean and secure because it is part of the ground path too.

The bed must be electrically bonded to the frame which is/should be bonded eventually to BATT negative...viola, the path is complete.

The lead buttons on the bottom of the light bulb must be clean..you can cut a little piece off of each pimple to get them shiny and fresh.

A ohmmeter should verify all these connections pretty easily.

Stuart

they usually ground thru the housing to the assoc. bracketry. i have rewired all of mine to LED (but the concept is the same for incandecent bulbs) include a multiwire cord that has a ground wire that i then ground to the wiring harness AND to the rear frame area. I'm just that way I guess, not wanting anybody to stop me for some silly light out issue, i guess. But this just goes to show that I use a separate ground wire to be sure all is working correctly.
http://s67.photobucket.com/albums/h298/1951otter/?action=view&current=587685-R1-032-14A.jpg
http://s67.photobucket.com/albums/h298/1951otter/?action=view&current=587685-R1-036-16A.jpg
and you have to when wiring LED's

Double check the filiments, wire brush the bulb housing as well as any internal contacts to the housing & socket to eliminate any surface corrosion. make sure your socket springs are good and the wire 'button' is not an 'open' circuit. (pulled out). sometimes adding a lock or star washer to the housing bolt adds to better housing grounding. maybe even run an extra piece of heavy wire from bed to rear of frame.
good luck

Hmm.. so then there shouldn't be a third wire? I'm wondering if I need to take the housing and bracket off and hit all the contact points with a little sandpaper. Or I guess I could run a third wire for the ground.

I'm really surprised that the grounding is through the housing and bracket. I really thought there should be another wire. Any other thoughts out there?

After you clean to bare metal where the ground contacts are made, that bare metal will soon rust and corrode. Some people suggest using non-conductive dielectric grease to minimize the corrosion; however, a conductive anti-corrosive grease is far superior at grounding points.

"Kopr Shield Colloidal Surface Treatment
Kopr-Shield compound is a unique homogenized blend of pure, polished colloidal copper, rust and corrosion inhibitors that simultaneously protects, lubricates and enhances the conductivity of the mating surfaces to which it is applied. Extremely adhesive, Kopr Shield compound flows smoothly into uneven contours and voids, making application easy, protection and lubrication complete and positive. A stable compound, it will not settle-out, thin, thicken, harden or dry out under the most severe environmental conditions."

Eastwoods and many electrical-contractor supply-houses sell this product.

Greg,

Tim speaks the truth on all points. If you want a third wire for ground that's perfectly fine. Many of today's housings are plastic which requires this ground wire anyway. If you choose to run a third wire to ground the housing (or any other electrical item) the connection points must be clean and well attached...just like the housing/bracket should be. It's sort of like "six of one, half a dozen on the other" as I see it.

Many folks don't stop to think that even though you don't see it, the ground path is really a 'wire' that completes the circuit to ground..it just takes the form of a bracket or a frame rail or a fender etc.

Stuart

Thanks for all the help. I ended up filing the bracket slightly where the nuts and bolts attach, testing for continuity at each step. Once I put the bracket back on, I got continuity from the light bulb socket to the battery ground. After hooking all the wires back up my lights are working correctly!!! This is good, since I originally thought my problems were with the in-cab light switch.

Ok, so here is a question for those doing frame-off restorations. If you paint your tail light bracket and the tailgate where it attaches, won't you fail to get a good ground when you reassemble everything? Or from the factory, I wonder how the ground path was ensured given the painted parts?

Greg,

On the factory question, my unprofessional guess is that when the mounting bolts were tightened, they bit through the paint enough to give a good ground path. Isn't this always where you find the beginnings of rust, right around where the fastener was tightened?

Stuart

Mostly that's true Greg. So when doing a ground off one has to make sure that grounds are good. During our ground off I have added a (green) ground wire to the wiring harness I made, incorperated a heavy braded ground wire to the engine/transmission, radiator frame, drivers inner fender (where i have a bank of relays), that inner fender to truck frame as well as cab floor, gas tank and bed to the truck frame. I have coated all these with NCP-2, an antioxidation/corrosion paste, mostly because they were/are bare metal. I also make sure that the threads that hold the grounding bolts (bare metal), are clear of paint. When not doing the extra grounding you must/should scrap away some areas that get bolted together and hope (usually they do) bond or make contact. Years cause rust and corrosion also the nuts loosen that cause the bond to fail.
That's why it's best to check your ground first during an electrical problem. Then go figure out why something isn't working.

Greg & Stuart,

My Suburban went through a total restoration. In almost all cases, as Stuart describes above, installing screws into the sheet metal established a good ground. A continuity-check assured the grounding. I then unscrewed each screw and applied Kopr Shield to the screw and dabbed a little into the hole in the sheet metal (using a fine-tipped brush).

So far, I have only had problems with one grounding inside the "case" of one of the side-mounted accessory dual-rear tail/stop/signal lamps.

I also use Kopr Shield (a conductive anti-corrosion paste) on my battery posts and on all my body/frame grounding straps (00 gauge). My 6v starter turns very nicely.

By the way, a ground strap from the head (one of the coil-bracket bolts works nicely) to the firewall (one of the fender-brace bolts works nicely) assures an excellent grounding to the cab sheet-metal. I dimly recall that this is specifically required as apart of the installation instructions that came with the 1954 radio.

Tim

Thanks for all your input. I'll keep all this in mind next time I have an electrical problem, and certainly if I ever get to do a total restoration of my truck. I think I'll also have to get some Kopr Shield or equivalent for future electrical work.