Brake lights
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Brake lights
I have a 65 ford f100 and recently my brake lights have not been working. When key is turned on my taillights come on rather dim even though the headlight switch is off. I replaced the headlight switch but the taillights are still dimly lit. The turn signals work but no brake lights and taillights are on whenever the key is on position. Any suggestions would be appreciated. 1 st time post so thanks for understanding.
Fleet Owner
Joined: Jun 1999
Posts: 24,552
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From: Creedmoor, North Carolina
mustangpt, Welcome to 
and the Slicks Forum. 
The ign switch needs to be on for the brake lights to work when the pedal is pressed, but not if it isn't. The brakes and turn signals share the same wire and bulb filament. Tail lights are on a separate wire and circuit.
Check around the rear bumper area, see if there is a trailer light access wire setup back there. A lot of times that can be the culprit.
Bet it is not too complicated.
John
and the Slicks Forum. The ign switch needs to be on for the brake lights to work when the pedal is pressed, but not if it isn't. The brakes and turn signals share the same wire and bulb filament. Tail lights are on a separate wire and circuit.
Check around the rear bumper area, see if there is a trailer light access wire setup back there. A lot of times that can be the culprit.
Bet it is not too complicated.
John
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Thanks John for tip. However I do not have any wiring set up for trailer lights or towing. I'll double check grounds but still curious as to why 2 wiring issues at same time. Wiring diagram shows turn signal switch as being connected to both brake lights and obviously turn signals as well as ignition switch. Short of replacing all 3 switches I guess I'll have to test those 3 circuits to see which one could be at fault. Also wondering if brake pressure switch on master cylinder could be culprit for brake lights not working. But I don't think this explains why taillights are on when headlight switch is off even when key is on.
Lead Driver
Joined: Aug 2003
Posts: 6,305
Likes: 18
From: Boulder Creek, Ca
1st and foremost; Welcome to FTE: As Schuey noted check the ground, found in many cases electrical gremlins can be traced back to faulty ground, a volt meter will be helpful. Had a similar experience and found the offset 2 pin taillight socket became corroded and effected the circuit, also verify the correct bulb is installed??
Posting a diag. link from 65 wiring manual:
http://i300.photobucket.com/albums/n...WireDiagP7.jpg
As Schuey noted check the ground, found in many cases electrical gremlins can be traced back to faulty ground, a volt meter will be helpful. Had a similar experience and found the offset 2 pin taillight socket became corroded and effected the circuit, also verify the correct bulb is installed?? Posting a diag. link from 65 wiring manual:
http://i300.photobucket.com/albums/n...WireDiagP7.jpg
Freshman User
Joined: Jul 2014
Posts: 40
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From: Denver
1st and foremost; Welcome to FTE: As Schuey noted check the ground, found in many cases electrical gremlins can be traced back to faulty ground, a volt meter will be helpful. Had a similar experience and found the offset 2 pin taillight socket became corroded and effected the circuit, also verify the correct bulb is installed??
Posting a diag. link from 65 wiring manual:
http://i300.photobucket.com/albums/n...WireDiagP7.jpg
As Schuey noted check the ground, found in many cases electrical gremlins can be traced back to faulty ground, a volt meter will be helpful. Had a similar experience and found the offset 2 pin taillight socket became corroded and effected the circuit, also verify the correct bulb is installed?? Posting a diag. link from 65 wiring manual:
http://i300.photobucket.com/albums/n...WireDiagP7.jpg
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Fleet Owner
Joined: Jun 1999
Posts: 24,552
Likes: 74
From: Creedmoor, North Carolina
Thanks John for tip. However I do not have any wiring set up for trailer lights or towing. I'll double check grounds but still curious as to why 2 wiring issues at same time. Wiring diagram shows turn signal switch as being connected to both brake lights and obviously turn signals as well as ignition switch. Short of replacing all 3 switches I guess I'll have to test those 3 circuits to see which one could be at fault. Also wondering if brake pressure switch on master cylinder could be culprit for brake lights not working. But I don't think this explains why taillights are on when headlight switch is off even when key is on.
A fact, three wires go to the back of the truck along the drivers side frame rail. One is for the tail lights the other two are for turn signals and brake.
Many times there are prior wiring mangles in the rear bumper area that you may have missed if you have not given it a good inspection. Corrosion and bad grounds many times cause the issues that you mentioned.
John
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More Turbo
Joined: Oct 2009
Posts: 708
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From: Pahrump, Nv.
Go to the brake light switch, pull the wire up on each terminal about 1/4 inch, leaving the wires on. Put a screw driver blade across both terminals it will by pass the switch. If it works the switch should be good. Check and make sure the bulbs are put in correct.(they will go in both ways but only one way is correct.) I would trace the complete harness the wire or wires could be chaffed. That exposed wire on the frame or other metal could be your problem. Make sure you have a ground strap from the cab to the frame. Good luck.
Fleet Owner
Joined: Jun 1999
Posts: 24,552
Likes: 74
From: Creedmoor, North Carolina
Go to the brake light switch, pull the wire up on each terminal about 1/4 inch, leaving the wires on. Put a screw driver blade across both terminals it will by pass the switch. If it works the switch should be good. Check and make sure the bulbs are put in correct.(they will go in both ways but only one way is correct.) I would trace the complete harness the wire or wires could be chaffed. That exposed wire on the frame or other metal could be your problem. Make sure you have a ground strap from the cab to the frame. Good luck.
John
Cross-Country
Joined: Sep 2014
Posts: 60
Likes: 2
I just had to do a rewire on my tail lights, puzzled my head until I out, out of a lark, attached a home made grounding strap to a freshly sanded piece of metal. They work wonderful now, it was the sheild two wire style. There had been so much paint and rust on the frame that it wouldn't ground properly.
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