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Old 04-14-2012, 04:46 PM   #1
goathearder
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Rear brakelight/turn signal wiring help

So recently I have found that my passenger rear brake light/turn signal isn't working. I replaced the bulb to no avail so I pulled out the multimeter and started digging. Here is what I found and I have no idea what could be wrong:

1) The taillight (when headlights are on) works. The bulb is a dual filament, 1 for taillight, 1 for brakelight/turn signal. The taillight works just fine.

2) The yellow wire seems to deliver the brake/turn voltage. Here is where it gets weird. With the bulb OUT, the yellow light delivers the voltage I would expect. With the bulb in, it goes from proper voltage to 0 voltage, What the heck???

I thought it might be the turn signal socket so I replaced that, no luck.

I thought it might be some wiring so I bypassed everything and went straight to the plug and ground, still nothing.

Everything else (side light and backup light) work over there so I am completely stumped at this point. All fuses are in tact and everything works on the drivers side.

The reason I noticed this in the first place is cause when I use my right turn signal, the arrow just stays green, doesn't flash at all. And here is the extra weird part, when I try the right turn signal, nothing works (front or rear) when I have the flashers on, the front passenger flashers work just fine.
Also, when I put the flashers on, both front flashers and the drivers side rear flasher work.

What am I missing here???

Last edited by goathearder; 04-14-2012 at 05:23 PM.
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Old 04-14-2012, 05:11 PM   #2
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So did you check the grounds, that usually happens when there is a bad ground on the tail light.

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Originally Posted by goathearder View Post
So recently I have found that my passenger rear brake light/turn signal isn't working. I replaced the bulb to no avail so I pulled out the multimeter and started digging. Here is what I found and I have no idea what could be wrong:

1) The taillight (when headlights are on) works. The bulb is a dual filament, 1 for taillight, 1 for brakelight/turn signal. The taillight works just fine.

2) The yellow wire seems to deliver the brake/turn voltage. Here is where it gets weird. With the bulb OUT, the yellow light delivers the voltage I would expect. With the bulb in, it goes from proper voltage to 0 voltage, What the heck???

I thought it might be the turn signal socket so I replaced that, no luck.

I thought it might be some wiring so I bypassed everything and went straight to the plug and ground, still nothing.

Everything else (side light and backup light) work over there so I am completely stumped at this point. All fuses are in tact and everything works on the drivers side.

The reason I noticed this in the first place is cause when I use my right turn signal, the arrow just stays green, doesn't flash at all. Maybe that means something???

Also, when I put the flashers on, both front flashers and the drivers side rear flasher work.

What am I missing here???
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Old 04-14-2012, 05:26 PM
Posted in reply to imiceman44's post starting "So did you check the grounds, that..."
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Originally Posted by imiceman44 View Post
So did you check the grounds, that usually happens when there is a bad ground on the tail light.
Yep, I checked the ground and it doesn't seem to make any difference. From what I can tell, there is 1 ground that is spliced into three grounds for the different bulbs. I even took the bulb in question and ran its ground straight to ground without the other three and still the same issue.

Do you think the ground location could be bad? With all the other lights working I figured the ground location was good and didn't change it but maybe I should try a different ground location?
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Old 04-14-2012, 05:43 PM
Posted in reply to goathearder's post starting "Yep, I checked the ground and it..."
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Yep, I checked the ground and it doesn't seem to make any difference. From what I can tell, there is 1 ground that is spliced into three grounds for the different bulbs. I even took the bulb in question and ran its ground straight to ground without the other three and still the same issue.

Do you think the ground location could be bad? With all the other lights working I figured the ground location was good and didn't change it but maybe I should try a different ground location?
Well I don't know what you mean by ground location, but I would grab a wire from that ground to a sure spot on the body or frame and see if there is a difference.
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1997 GMC savana
1991 crew cab no drivetrain for now
1989 Jetta 4 speed DD
1985 suburban 3/4 ton 4x4 6.2TD
1977 K5 chalet
1974 suburban 1/2 ton 4x4 350
1970 Chevy LB 2wd 396 BBC 700R4
1967 Pontiac Firebird 400
1965 Chevy Corvair coupe 110
1962 Chevy Corvair Van Greenbriar
1986 Honda 250 XL
1985 Honda Magna V45
1970 Wreidt 19' jet drive boat 455 olds
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Old 04-14-2012, 08:41 PM
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Well I don't know what you mean by ground location, but I would grab a wire from that ground to a sure spot on the body or frame and see if there is a difference.
I just mean the hole where the screw is holding the ground in. I will try a different location for that and see what happens.
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Old 04-14-2012, 08:50 PM   #6
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Ok, here is a new development.

If I jump 12v straight to the yellow wire, the second filament lights up exactly like it should. Now I am thinking the problem isn't at the light itself but maybe wherever power is getting sent to the wires?

Could there be something in the actual turn signal switch or somewhere else that could be affecting this? A short up there or something?

What really has me thinking that is that the right signal doesn't even activate the lights in the front even though they operate fine with hazards and parking lights.
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Old 04-15-2012, 09:07 AM
Posted in reply to goathearder's post starting "Ok, here is a new development. If I..."
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Have you tried another bulb? I just put in two new bulbs because I knew one was burned out but I didnt have any brake lights. Everything else worked, just no brake lights. After the new bulbs I hop in to go to my parents and the driver side turn signal wont work, it just lights up solid. Turns out it is something with the bulb, you could wiggle it and it would work. I put the old one back in that was still good and it worked fine. The new one felt a little loose in the housing and the old one didnt. That didnt however fix my brake light problem so I am gonna have to dive deeper to figure that out. Just havent had time.

Checking your new bulb is just a K.I.S.S. (keep it simply stupid for anybody that doesnt know) method that gets overlooked alot. It has gotten me several times, lol. New parts can be bad from the start. I worked on a brand new pontiac solstice one time and during the new inspection on it I found the high beam headlights didnt work. Turns out it was a fuse, so I change the fuse and hit the high beams and they worked for a little bit and then popped the fuse again. So I started looking into it, wasted too much time on it really. Turned out to be bad bulbs, even though they still worked they happened to be burned out but the filament happened to melt back together causing them to still work. It was like that on both bulbs, once you pulled them and inspected them you could barely see it. Pain in the butt but I guarantee you I will NEVER forget it. LOL.
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Old 04-15-2012, 09:13 AM   #8
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I would put money on the turn signal switch.

Just did a 90 something chevy almost the same problem except on one side, turn signal switch fixed the problems.

One more cheap thing to check though is your flashers. the 2 round things that go in the fuse box. I don't know how to check em I just replace em. They are pretty cheap
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Old 04-15-2012, 09:26 AM
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Hope its not the trun signal switch but it sounds like it may be. I bought the steering wheel removal tools from napa and bent them getting my steering wheel off. Getting the wiring down the column was a total hassle too. At least napa gave me my money back for their wussy tools. For a long time my truck would pop a taillight fuse but only when the headlights were on. I replaced the headlight switch unnecessarily and it turned out to be a spot where the insulation wore off and touched the frame, it hid it's self pretty well. Sounds like yours isn't a short though since it never pops fuses.
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Old 04-15-2012, 02:37 PM   #10
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Well, turns out it was the turn signal switch. Bought a new one and plugged it in and all is well. Just in the process of putting the steering column back together. What a PITA.
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