GtoRockz

I just cant figure it out or maybe i am missing something?
577 bulbs for the third (High mount) brake light do not work.
Tested the socket with my lighted tester and there is power when the bakes are applied. Tested the bulbs direct to my rv battery with my test light.. when connected my tester lights up but bulbs do not.. doesnt make sense because current has to flow through the glass to light my tester.
Purchased two brand new bulbs and they do the same thing???

How could new bulbs not work when directly hooked to 12 volts???

Any help appreciated

92RS_Ttop

iTrader: (3)

The first 2 things that come to mind:

Are you getting a full 12V at the light sockets? Not enough voltage for the bulbs can still light a test light.

Is there a ton of bulb grease in the sockets that can prevent the contacts on the bulb from making good contact to the socket? I've had this problem with my truck. PO smeared a ton of that stuff in the taillight sockets.

GtoRockz

No grease, sockets look clean. I put all four bulbs right onto a brand new freshly charged deep cycle battery and the tester lights up bright when i touched the other end of the bulb. Current is flowing through the bulbs but they do not even light up dim.

Here are the bulb specs: #577 MINIATURE BULB DOUBLE END CAP BASE - 12.8 Volt 1.4 Amp T4-3/4 Double End Cap (SF6/6) Base Bulb, 21 MSCP C-8 Filament Design, 1,000 Average Rated Hours. 1.72" Maximum Overall Length.

92RS_Ttop

iTrader: (3)

Are the end caps loose to the glass? I hate that type of bulb, I've had lots of problems with them in the past where they will show current on a test light and a DMM but will not light up. I think the seal breaks easily between the end caps and the glass center and the gas inside escapes or the wire from the sides to the filament breaks preventing them from lighting properly.

I'd try some new bulbs. You can also try using some needle-nose pliers to close up the tabs in the socket a bit to be sure they are gripping the bulb tightly and making good contact.

GtoRockz

Have brand new bulbs and the original ones do not look bad, nothing broken.
Has to be a voltage converter or something.. these bulbs say 12.8 volt but 12 volts does nothing.. you would think they would glow orange even if there was not enough juice.

92RS_Ttop

iTrader: (3)

12.8 vs 12 shouldn't make a difference. When the car is running, you'll get more than 12 to the socket anyhow. Usually you'll see 13-14v with the engine running. Are you absolutely certain you're getting 12v at the socket? Have you put a DMM on it, or did you just use a test light?

If it was my car, Id test the bulbs using some jumper wires from the socket to the bulb. If you get light, its the socket, if not, its the bulb.

GtoRockz

I used a test light, do have a meter somewhere just have to dig it out.
Are you saying the test light wont work as a jumper?

92RS_Ttop

iTrader: (3)

It will work as a jumper, but it can't measure the amount of voltage in the line, or the amount that voltage drops as it passes through the bulb which is what you need to measure. I would also maybe try a regular 194 bulb. The kind used in the side marker lights. Just to see if it lights another automotive bulb up. Not just the test light. You may have a low voltage at the socket, and the voltage drain of the bulb in the test light is enough to keep the 577 bulb from lighting.

GtoRockz

Good idea, i will jump a different type bulb and see what happens.

Billy_Bob

They are not lighting because they are a hunk of junk, as are a lot of products these days!

I had similar bulbs last only a week, then another last only 2 weeks, and one brand new bulb of that type only lasted a few hours!

I got fed up and replaced them with LED lights and these are still working. I've had them in for 2 months now.

I got my replacements here...
http://www.superbrightleds.com/cgi-b...6.7185&next=50

And the replacements are called "Festoon" bulbs. You need to scroll down about 3/4 of the way on the page.

The kind I got have a little circuit board on them and I was not sure they would fit. (And by the way this was for a different car than yours.)

Then they go by mm for measuring. So need to measure your bulb.

Also the brightness for these bulbs at this web site is confusing. They use different units of measurement. Here is what I basically figured out...

LED Lumens
lm is total luminous flux flowing from the LED in lumens
(mlm=millilumens)

cd is the luminous intensity in candelas of the light
(mcd=millicandela)

mlm, a unit for luminous flux, corresponding to 1/1000 lumen
4700 MLM =7000 MCD

1000 millicandelas @ 30 degrees beam pattern = 0.214 lumens

afremont

You can't use the test light to supply power to something else. The lamp in the test light already uses a fair amount of current, but it also acts as a resistor when it's lit.

GtoRockz

Thanks guys, i realized about the test light. Cleaned the contacts and squeezed them tighter and put it back together with the new bulbs. Still dont think it works but need to get someone to hit the brake pedal for me to be sure.
May go the LED rout if it still is not working.

BigBadLou

iTrader: (3)

You said you tested the positive side of the third brake light. Did you also test the negative side, aka ground? You can connect the test light negative terminal (usually the alligator clip) to one end of the light socket and then stick the probe into the other end of the socket. That way, you're testing only that circuit with no other grounds involved.

Hope this helps.
Lou

GtoRockz

yes, that is how i tested it and it is getting power and has a ground.

IROCVegas

ok... do you get continuity across the bulb with and without the little caps?