Clearance/Marker light question

[groovzilla]

all,

on my 65 24' tradewind, only 2 of the 10 clearance lights are functioning.

i'd like to repair the originals on the trailer since they are in decent condition however i don't want to go nuts and put hours of labor into each one.

as i understand it, the positive(hot)feed is on the bottom of the bulb(blue arrow in photo) and the ground on the bulb is the brass cylindrical portion(red arrow)

is this correct??
i ask because i am completely stumped???

i removed the lenses and on the bases, completely cleaned all brass contacts as well as the round ground collar that touch the perimeter of the brass contact(ground) on the bulbs. i also cleaned the bulb contact points.

i used my 12v tester and using the trailer skin as the ground, i tested the (hot) wire attached to the brass contact on the clearance light bases and all are getting juice - i also tested the brass contact points where the tip of the bulb touches and all are getting juice.

**when i try using the round ground portion of the clearance light base while testing i get nothing. even on the 2 lights that are functioning, when i use my tester i get no ground from the round ground contacts surrounding the bulb??

so my question would be am i incorrect assuming the round portion of the clearance light base that surrounds the bulb is NOT the ground??

...and does anyone have any idea what the heck is up with these lights?? again i am getting hot juice to all lights so it is some sort of disconnect within the light base itself - wondering if i can maybe solder and reground the bulb surounds possibly?

[Al Boondy]

A bulb doesn't care what contact is hot or ground and it really doesn't matter.
Generally the bottom is hot but fixtures vary.
The ground is connected to the skin thru the screw or rivets attaching the fixtures. You could have corrosion on these screws/rivits.

[HowieE]

I am assuming you have tested, by light them in a good socket, each bulb and they are good.

Ground or the path to ground is the most common problem on older 12 volt circuits.

Put your tester on the center contact of the light socket. remove one of the screws and touch the trailer skin at the empty screw hole. If you see voltage there the feed wire and the trailer skin are good and complete the circuit. Now touch the head of the screw that is connected to the light socket. If the shows voltage touch the brass strapping under the screw. If that is good touch the socket itself. If that is good clean the tabs on the side of the bulb and put it in the socket. The point where you lose the appearance of voltage on your tester is the problem. Clean that area and continue the test till the bulb will light in each socket.

[groovzilla]

thank you for the posts!

[groovzilla]

repairing the grounds on each of the 8 lights that aren't working would be a major task - i decided to forego trying to repair the clearance lights and buy new replacements.

just ordered all 10 from vintage trailer supply.

[Boxite]

I believe it's possible you've not used your 12v tester correctly. It is designed to "complete" a circuit. IE, when you place one lead on the skin of the trailer and the other on the center-contact you are completing a circuit and see the tester indicate 12 volts.
But when you place one lead on the skin and the other on the base of the bulb-holder you are actually placing both leads on "ground" connections...therefore no current flows...and no voltage (difference) is indicated between the two leads.
To test a proper "ground" ....you do not need to test for voltage. You need to test for "resistance"... IE, you need to generate a current to see if the circuit is completed.
A method to do this is: 1) do as you've already done by testing that 12 volts are available at the center contact.... then, 2) keeping one lead on that center contact, place the other lead on the brass "base" of the bulb-holder. If the 12 volts is still present then the lamp should illuminate when it is reinstalled. (Another method is to test for continuity with an "ohm meter", but beware of using an Ohm Meter if voltage is present as damage might occur to the meter.)
(In fact, as you should now see, the best/fastest/simplest method is to place one lead on the center contact, and the other on the base to begin-with...and if voltage is present the circuit is good. The most likely problems now are either a bad bulb/lamp or the base is not in contact with the center contact when installed....<check the spring beneath that center contact pushes the center-contact against the center terminal of the bulb when it's installed.)