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620 no brake lights no hazzards


Jbone32

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Turn signals all work no brake lights and when i pull dukes of hazard switch it shuts off signals but no hazzard ..i think it may be two separate issues as theres  no click from under dash when hazard switch pulled..swapped the flashers under the dash with hazards and neither work..swap em back and just have signals again..no brake

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The brakes and signals share the same bulb filament and wires. If the signals work then the wiring and bulbs are there and working. To operate, the turn signal switch disconnects the brake on the side that being signaled or the bulb would just stay lit while braking.

 

 Go the the turn signal switch and find the Green/Yellow stripe wire. This is the brake light signal. Test it for power when the brake is applied. Follow that wire into the switch it must be broken or something.

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Well i followed green and yellow wire  that gets 12v when pedal is depressed it disappears deep into harness ..im about to pull the seat out and see where it goes but .the factory rear harness only has these colors.. red black stripe, white red stripe, white black stripe, green blue stripe,and black and none of them probe out power when pedals depressed 

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Edited by Jbone32
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20 hours ago, datzenmike said:

The brakes and signals share the same bulb filament and wires. If the signals work then the wiring and bulbs are there and working. To operate, the turn signal switch disconnects the brake on the side that being signaled or the bulb would just stay lit while braking.

 

 Go the the turn signal switch and find the Green/Yellow stripe wire. This is the brake light signal. Test it for power when the brake is applied. Follow that wire into the switch it must be broken or something.

 

Green/Yellow is the stop signal into the turn signal switch. There, it becomes the Light Green/Black strip for the right rear and the Light Green/Red stripe for the left rear.

 

Light Green/Red and Light Green/Black are the stop and turn signal wires to the rear. Should have 12v when brake applied. If not then the problem is back towards the turn signal switch.

 

IMG_20210405_155812883.thumb.jpg.bc45d09

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1 hour ago, datzenmike said:

Go the the turn signal switch and find the Green/Yellow stripe wire. This is the brake light signal.

Rear wires you mentioned in rear do not give voltage when pressed..All of the terminals on the switch are constantly hot at switch even when brake is pressed turning on signals makes the probe flash brighter on probe..the brake switch at pedal has a terminal thats always hot that comes from the signal switch in first picture and one that lights up when pressed thats goes out to firewall both are green and yellow..if thats right then im thinking something is cut somewhere..btw non related what is that box on the firwall do in this picture?..thanks again mike

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Edited by Jbone32
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Just realised my probe only tests continuity..lol 

Somebody should probably delete this post so somebody as dumb as me dosnt follow it in the future.. sorry...so the brake wire at switch has no voltage when depressed but pedal has continuity should it have 12v in one side?

Edited by Jbone32
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All hazard switched disconnect the turn signals to work but re connect them in the off position. That's normal. Did you swap the two flasher units?????? If 4 ways start working then the flasher unit was bad. Simple.

 

1 hour ago, Jbone32 said:

At the switch they are both green with yellow stripe one goes to the turn signal switch and has no power the other goes out firewall thru harness "pic earlier" appreciate the help

 

The brake light would not go through the firewall it would go to the tail lights through the L&R turn signal wires. Light Green/Red and Light Green/Black

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15 hours ago, datzenmike said:

 

The brake light would not go through the firewall it would go to the tail lights through the L&R turn signal wires. Light Green/Red and Light Green/Black

I followed the turn signal wires and they go from the signal switch through the harness and turn off and go under seat and out the back..the brake light wire keeps going thru harness out firewall..this wire dead shorts to ground when depressed and blows fuses when i hook 12v to one side from fusebox..aside from further tearing apart harness im thinking of installing some aftermarket lights as 3 days on brake lights is not normal for me...this truck is driving me nowhere but crazy

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 No.

 

The power wire from the fuse box feeds several things, like the 4 way flasher, and through the fire wall as a Green/White wire to power the horn relay. As a Green/Yellow wire it goes to one side of the brake switch, through it and to the turn signal switch ONLY, as a Green/Yellow wire. Nothing else is connected to the 12v passed through the brake switch when the peddle is depressed. At the turn signal switch it splits onto the Light Green/Black and the Ligh Green/Red wires.

 

If blowing the fuse, a short to ground can be anywhere between fuse box, 4 way flasher, brake light switch and the horn relay.... ALL are powered from the same fuse.  Find the horn relay on the driver's side of the radiator support, I think on the '73/'74 and unplug. See if that helps

 

 

 

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1 hour ago, Jbone32 said:

when i hook 12v to one side from

12volt should come from the fuse box to the switch at the pedal. Find the 12volts .

If I understand you correct your bypassing the 12volt and hooking it straight up to the switch then it pops the turnsignal fuse.?????

 

 

OK I think Mike got this covered

 

as mike said unplug the horn relay. Maybe there is not horn and its grouning out?

unplugg the 4 way flasher and see if that does anything.

 

the brake lights should come on either way if those worked or not I would think

Edited by banzai510(hainz)
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