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brake light issue '78 k5, Have Diagram, still confused!*SOLVED*

M

MuzachMT

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So,
I noticed I had a driver side brake light out, tried a bulb, no luck. Redid the ground under the housing, nothing. So I started playing with the wires in front of the rear bumper. Now the driver side brake light works, both blinkers work, flashers work, tail lights work, but NO pass. side brake light!!! There are trailer lights hooked up with one green wire coming off to the drivers side, which I disconnected in my messing around. Is this a complete circuit where as that trailer wire needs to go somewhere? Also the 4 prong plug back there is missing a tab on the female side (which I now know is supposed to be like that).

Also, drivers side blinker will not blink, just stays on, but flashes with flashers on. Will the blinker switch cause the brake light to not work?? And why did one side work, and not the other, now the opposite?
ahhh! :laugh:
 
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Update:
I completely chopped out the 4 prong to 3 prong connector deal on the driver side and just wired the stuff right together...fixed everything! Only problem now is driver side blinker doesnt blink on its own, and hazard doesnt flash on driver side. Probably just the flasher fuse thing on the fuse box maybe? Or would that be the blinker switch inside the column? (if thats the case, I will manually flash it, not going through that p.i.t.a when I can manually make it look legal) :P
 
Ok, I have worked on some very complicated electronic systems over the years, but I just cannot figure out exactly what your problem is..........:D

But, I do have a couple of suggestions.
First, notice that there are two green wires in that setup, dark and light green.
Make sure you have not crossed them. Colors can fade or change some over the years.
Now, when you say driver side does not blink, do you mean at all, or just the back bulb?
And what happens when you turn it on? Does everything just stay lit? Also, be sure and wiggle the e flasher switch when you have just the turn signal on.
They can get dirty from non use and cause strange problems. Usually moving them from side to side changes things, and often just switching them on and off a few times cleans the contacts.
 
The dark and light green's are still brightly colored and easily identified. The driver's side front or rear will not blink with the turn signal engaged, it just stays lit (front rear drivers and dash indicator). And the drivers side rear will not flash with the hazards on, but the all others fr fl and rr all do. I have not tried playing with the hazard switch while the turn signal is engaged, but I have turned em on and off multiple times as I heard they can cause problems. Thanks much, I will try that next, if not that, replace flasher fuse thing, (silver round deal), if no fix there, assume it's the blinker switch itself in the column.
 
OK, makes more sense now.

The blinker module works off of current.
It has an internal heating element that gets hot and causes a bimetal strip to bend.
And is pretty much the same left and right.
Odds are if it works on the left, then its good.

But, they are cheap, and not hard to change. Just remember there are two, one for the e flasher and one for the turn signals.

Usually when they just stay on, it means that you have a blown bulb. It was designed that way so that you would have an indication when one goes out.

With one bulb not drawing current, the flasher unit does not see enough current to get hot enough to flash.

Be sure to check the front bulb and socket on that side too.
If the turn signal indicator on the dash glows faintly when you turn the head lights on, it means you have a bad ground.
It can be internal to the socket.

The socket is grounded by that ground wire you checked, but there is a common ground terminal inside the socket that the side of the bulb touches. If it is dirty, or the ground wire connection to it is bad, then you will have all kinds of weird problems.

If the drivers side bulb lights up with the turn signal, but does not when the E flasher is on, I gotta suspect the E flasher switch.

Try checking the ground on the front bulb, and take the bulb out of the front and back and look at that side terminal.
If it looks corroded, do not bother cleaning it. Its probably corroding because its getting hot from a bad internal connection.
Just go ahead and change it.
 
xsmokey11499x said:
im kinda having a similar problem.. but im not goin to thread jack.. Ill just make another!
Click to expand...


Feel free to post here, I'd be interested to hear your issue.

And thank you Fordum for the helpful info.

One question, you say there are two blinker modules..I see the one up top on the fuse block, is this hazard or blinker and where is the other one?

Once it stops raining I will check the front. but seeing how the front flashes with hazards and stays on with blinker, I'm guessing the bulb is ok, but socket ground may be bad I suppose.

With everything said, could it still be the turn signal switch in the column? The whole lever seems pretty wobbly.
 
One question, you say there are two blinker modules..I see the one up top on the fuse block, is this hazard or blinker and where is the other one?
Click to expand...

Darned if I know. Its one of the fun parts of advising folks here for me. I don't own a GM product, I just know how they work, mostly.
There are plenty of folks here who can tell you, but its pretty easy to tell. Just turn on the blinker that works, and put your finger on the module. You can feel it clicking usually.
Plus, you can turn on the E flashers and listen closely. You can probably find it by the sound.

The turn signal switch can easily cause what you are seeing. It pivots on a center pin, and if it wears, some of the contacts cannot touch.
You can get where you can see the light reflected off a building or window from the driver seat.
Turn on the driver side blinker, and then move the lever up and down and see if it makes a difference.
If the switch is worn, you can usually get it to work briefly by moving it.
 
Hmm..
Turns out it was the turn signal switch all along! If I move it to just the right spot, both brake lights work fine (spot now marked with a sharpie so I can re allign it after using the blinker ((it is very loose)). Sanding down the grounds behind the light housing apparently fixed the turn signal not flashing problem.

But anyone having a similar problem...have someone watch your brake lights while you move the lever ever so slightly..and get your grounds real clean, mine were rust on rust, apparently rust is not very conductive :)
 
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And thank you very much Fordum for all the useful information. I will store it in my memory bank and hopefully make use of it someday, and I hope it helps anyone else who may have a common problem and comes across this thread. Very informative!
 
Glad you got it going. Yep, the brake lights go through the turn signal. And anything that cuts down on the current going to the blinker module can cause it to not flash.
 
my problem is when I press the brakes, the front blinker lights up and the Rear driver brake light doesnt.
The wiring is correct.

could my problem be the same thing, the switch?

also if I turn my right blinker on, Both front "blinker lights" flash
 
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