Testing light bulbs for internal shorts. :confused:

[JOET/CAMRY]

Hello, back in December 2004 I put in a post that went as follows >> Hello, My 1989 camry keeps eating up the lamp failure sensors like crazy. When I start my car then hit the brake pedel the indicator light on the dash comes on telling me there's a burned out bulb in the rear of car ; but the bulbs seem fine. the brake lights stop working. Have replaced this part 3 times in the last 6 months getting a used one from the junkyard. Does anyone know why this part keeps dying on me? Thanks. Joe. << I was told by a member of this fourm ( JDBord ) that one of the bulbs for the brake lights/tail lights might have an internal short in it (which would be the cause of the Lamp failure sensor going bad ) and I should check the bulbs using a multimeter to find out witch bulb was bad; and replace the bulb. Could someone please explain in detail how to check light bulbs for internal shorts. I have a drawer full of #1156 and # 1157 bulbs and all look good : filament not busted.. I know bulbs are very cheap in price but wanted to know out of curiosity! Also wouldn't a bad #1157 lightbulb be most likely the cause of the lamp failure sensor going bad as opposed to of a bad #1156 bulb. any help/advice would be appriceated.
Thank You, JOET/CAMRY

[Daniel M. Dreifus]

Check the wiring harness at the trunk hinge that flexes every time the trunk opens.
I repaired two of those wires couple years ago on my '94, then recently went back in and found three more that had broken (but still worked because they were still touching in the harness - only intermittent failure).
After soldering in sections of wire (first coiled around a wrench handle to impart flexibility) I realized that now the stress was all on the remaining two (previously repaired).
So I added the soldered in section of coiled wire on those also.
Lucky I went back in because one of them (slightly thinner than the other) was showing signs of stress flexing again.

[Daniel M. Dreifus]

Here's another possibility.
Make sure the bulb sockets are well grounded.
Could be you need to tighten clean or tighten a screw that holds them to the frame.

[JOET/CAMRY]

Originally Posted by Daniel M. Dreifus

Check the wiring harness at the trunk hinge that flexes every time the trunk opens.
I repaired two of those wires couple years ago on my '94, then recently went back in and found three more that had broken (but still worked because they were still touching in the harness - only intermittent failure).
After soldering in sections of wire (first coiled around a wrench handle to impart flexibility) I realized that now the stress was all on the remaining two (previously repaired).
So I added the soldered in section of coiled wire on those also.
Lucky I went back in because one of them (slightly thinner than the other) was showing signs of stress flexing again.

Thank you Daniel for the advice you gave about checking the wire harness where it flexes when the trunk opens/closes and about checking for proper grounding of the light bulb sockets;making sure their clean of corrosion,rust. Acctually the problem I was having has been fixed since late December. It was a internal short in one of the bulbs in the rear of the car that was causing the lamp failure sensor to burn out. I should have mentioned the problem was fixed in my post. I just wanted to know if someone could explain in detail how to test the bulbs for internal shorts using a multimeter. I have around 20 #1156 and #1157 bulbs.all look fine from outer appearence, but I know some have internal shorts. Thanks, JOET/CAMRY

[JOET/CAMRY]

Originally Posted by JOET/CAMRY

Thank you Daniel for the advice you gave about checking the wire harness where it flexes when the trunk opens/closes and about checking for proper grounding of the light bulb sockets;making sure their clean of corrosion,rust. Acctually the problem I was having has been fixed since late December. It was a internal short in one of the bulbs in the rear of the car that was causing the lamp failure sensor to burn out. I should have mentioned the problem was fixed in my post. I just wanted to know if someone could explain in detail how to test the bulbs for internal shorts using a multimeter. I have around 20 #1156 and #1157 bulbs.all look fine from outer appearence, but I know some have internal shorts. Thanks, JOET/CAMRY

WOW, I guess nobody knows how to test a light bulb for internal shorts. Particularly the #1157 which I think is the bulb for the brake lights. I was hoping to find out so I wouldn't have to replace light bulbs that didn't need to be replaced if (for example)1 bad bulb was causing the lamp failure sensor to burn out , etc.... It's odd how a light bulb can look fine (filements not broken) but still be defective. Hope to hear from someone about this topic. Thanks, JOET/CAMRY

[Brian R.]

Test the resistance of the ground (outer part of bulb) with the one or both center contacts and test the resistance between the two center contacts when there are two.

The resistance of the bulbs should be the same for all the bulbs for the contact to ground (the resistance of the filaments). The two filaments in the dual bulbs (contact to ground) will have two different resistances.

The resistance between the two center contacts should be the total of the resistances of the two filaments. These numbers will be the same for all the good bulbs. Any bulb that has a resistance substantially lower than the others has an internal short.

[hueroloco]

from reading your post it sounds like you have a brake light power circuit shorting to the taillamp circuit which is blowing the failure sensor.

If you've changed all the bulbs already, it isn't very likely that you would get a shorted bulb twice. It's not that common, but it does happen. Anyway, to test for a short in the 1157's you'll need a meter, an ohmmeter, preferably a digital one.

Test for resistance between the two terminals on the bottom of the bulb, there should be infinite resistance because they are two separate circuits.

let us know what happens. I think you probably have a wire or something inside the tailllight assembly that is shorted.

[Brian R.]

Originally Posted by hueroloco

Test for resistance between the two terminals on the bottom of the bulb, there should be infinite resistance because they are two separate circuits.

You are only partially correct. They are on separate circuits only when they are mounted in the car. They are connected by the common ground. The circuit you are measuring the resistance of, between the two contacts, is from one contact through its filament to the ground then from the same ground through the other filament to the other contact. I bet you a dollar that both filaments will light if you connect 12v between the two contacts on the bottom of the bulb.

As I said above, the resistance between the contacts will be the sum of the resistance of the filaments.

Also, it is not so strange that a batch of bulbs has many that fail in the same way. They are made one after the other and any fault in manufacturing of one bulb is likely to be carried over to the next bulb (or widget or whatever).

I bought 3 or 4 boxes of bulbs from a store and most were bad because of a fault in the insulator. As soon a I bought a different brand, my trouble stopped. When I looked closely at the bulbs, I could see that alot of them had a crack in the insulator base.

[hueroloco]

yeah, you're right brian

[Brian R.]

Interesting problem though...

[JOET/CAMRY]

Originally Posted by Brian R.

Interesting problem though...

Hello, Thanks alot Brian R. and hueroloco for the info. I broke out my digital multimeter and was testing away and found 2 bad bulbs out of the whole bunch. On the #1157 bulbs the resistance from the contact to ground was approx. 2.0 for one contact and approx.3.6 for the other contact (according to my multimeter) for practically all the bulbs. odd thing was when I added the mesurements together and measured the resistance between the 2 contacts on the bottom of the bulbs it turned out to be approx. around 3.8 to 4.1..... The sum of the measurment between the two contacts (on the bottom of the bulb) is defenitely lower than the sum of the mesurements(from contact to ground). Is 3.8 -4.1 a big difference compared to 5.6 (the sum of the 2 mesurments (contact to ground). IS EVERYONE COMPLETELY CONFUSED NOW!!! Thanks alot JOET/CAMRY

[Brian R.]

I wouldn't have predicted that would happen, but it doesn't surprise me either. Have you tried a different brand of bulbs also? Another brand may be more predictable from theory (contact-to-contact is the sum of the filaments). It may be that all the bulbs you've tested are bad and you are finding two different faults. Anyway, you've at least found one significant deviation in a couple of bulbs.

Originally Posted by JOET/CAMRY

The sum of the measurment between the two contacts (on the bottom of the bulb) is defenitely lower than the sum of the mesurements(from contact to ground). Is 3.8 -4.1 a big difference compared to 5.6 (the sum of the 2 measurements (contact to ground).

[hueroloco]

you got me really wondering on this one, so I measure the 1157's here in the shop and all were about 2.4 ohms.

one filament 2.0
the other .4 or .5

so did putting in good bulbs fix your problem?

[JOET/CAMRY]

Originally Posted by hueroloco

you got me really wondering on this one, so I measure the 1157's here in the shop and all were about 2.4 ohms.

one filament 2.0
the other .4 or .5

so did putting in good bulbs fix your problem?

Hello Hueroloco, That is odd we both had the same mesurement of 2.0 for one filament but you had a mesurement of .4 to .5 compared to my mesurement of approx. 3.6 for the other filament on the #1157 bulbs. The brand name of the bulbs I was testing is unknown. probrally some cheap bulbs from the dollar store,walmart,etc. Maybe my digital multimeter (Micronta) was acting up or I wasn't testing them properly. :confused: My car has been fixed since late December 2004.back in December I replaced all #1156 and #1157 bulbs in the rear of my car because of the problem I was having with the lamp failure sensor burning out when I hit the brake. I would replace this part just to have it burn out once again(when I would hit the brake). Found out from a member of this fourm that one of the bulbs for the brake lights (#1157)? MIGHT have an internal short in it which was probrally causing the problem. I replaced all the #1156 and#1157 bulbs in the rear of the car (just to be safe) and have had no problems with lamp failure sensor failure in my 1989 camry. My car is running great so far >knock on wood< ] Do the #1156 bulbs light up as well as the#1157 bulbs when the brakes are applied? Thank you for you help/input. take care.. JOET/CAMRY