1995 Ranger 3rd brake light LED issue

[pintobobster]

Good Afternoon All,

1995 Ford Ranger XLT 4WD Automatic 4.0L

Issue I am having.

3rd brake light slightly comes on "only when ignition is turned on", when brakes applied it does get brighter as should be.
no engine light (CEL), no other light issues, brake lights work, turn signal works, running lights work, stop lights work (even 3rd brake light), just this 3rd brake light issue coming on when key is in the run position or when truck is running? no other lights on.
someone stated 3rd brake light could do this if a bulb is burnt out or bad, so I put in the incandescent bulbs bypassing and removing the LED tail lights.
I have replaced all the following = multi-switch high-beam/hazard/turn/wiper, light switch, Rheostat switch, brake light switch at brake peddle, cruise control cut off switch (under hood at brake master cylinder), replaced hazard/turn signal relay next to steering column under the dash, also replaced LED tail lights, replaced 3rd brake light LED (have these for spares just in case??).
removed trailer wiring harness, cleaned all grounds at tail lights, under hood, checked all factory splice connections for corrosion placed dielectric grease.
All fuse's are working none blown.

What am I missing??
What could be causing this 3rd brake light to come on (dim but it is on and can be seen during the day or night).

what else could cause just the high/3rd brake light to be activated? bed cargo lights on 3rd brake light works as should be with no issue.

Also my or may not be related, But my cruise control has also stopped working. does not engage any more at any speed.

Thank You for any thoughts to help me check.

 

[sheep herder]

Does the 3rd brake light have a ground wire or is it grounded to the cab at the light? Bad ground is what it sounds like.

 

[pintobobster]

Does the 3rd brake light have a ground wire or is it grounded to the cab at the light? Bad ground is what it sounds like.

To access the ground for the 3rd brake light, would I need to pull the whole headliner off to gain access?
Or where is this grounded at? I do not see any grounding at the area of the light itself, Just the three wires, Brake, Cargo light, and ground.

 

[sheep herder]

I've never had to mess with one so I really don't know how it's wired. If the brake light and cargo light share a common ground, then the ground probably isn't the problem.

 

[sheep herder]

Wiring diagram in this thread. https://www.therangerstation.com/forums/index.php?threads/96-cargo-light-wiring-diagram.188750/

 

[Curious Hound]

It almost seems like your brake on/off switch is not working properly, ie; still making some contact even when the brake pedal is not pushed. If thats the case, it would also be applying power to the cruise "disable input" and that would prevent the cruise from functioning. Try disconnecting the brake on/off switch and see if the light goes out. If that works, replace the switch.

 

[pintobobster]

It almost seems like your brake on/off switch is not working properly, ie; still making some contact even when the brake pedal is not pushed. If thats the case, it would also be applying power to the cruise "disable input" and that would prevent the cruise from functioning. Try disconnecting the brake on/off switch and see if the light goes out. If that works, replace the switch.

Thank You for the reply, I replaced the switch and I have bypassed it. Disconnected the switch at the brake peddle completely and the 3rd brake light still came on when the ignition switched to on.

 

[pintobobster]

Wiring diagram in this thread. https://www.therangerstation.com/forums/index.php?threads/96-cargo-light-wiring-diagram.188750/

Thank You, This is for the cargo lamp, The 3rd brake light breaks off and goes to the Exterior lighting Wiring Diagram.

 

[Ranger Mark]

To access the ground for the 3rd brake light, would I need to pull the whole headliner off to gain access?
Or where is this grounded at? I do not see any grounding at the area of the light itself, Just the three wires, Brake, Cargo light, and ground.

Just FYI, the ground is located at the dome light. At least mine is. '96 4x2

 

[pintobobster]

Just FYI, the ground is located at the dome light. At least mine is. '96 4x2

Thank You,
I will dig into that this next weekend,

 

[Ranger Mark]

The more I think about this, it sounds like you have an induction issue. If the insulation is thin and it runs next to a large power wire you could theoretically induce enough voltage to slightly light the bulb. These wires run down the B pillar behind driver then along the floor.

 

[Curious Hound]

The more I think about this, it sounds like you have an induction issue. If the insulation is thin and it runs next to a large power wire you could theoretically induce enough voltage to slightly light the bulb. These wires run down the B pillar behind driver then along the floor.

I doubt that there's enough ripple to the DC to do that. Even if it was AC, at 12volts, it would be doubtful.

Furthermore, it would only work when the neighboring circuits are operating - actually drawing current. Ie; the dome light and cargo light would have to be on.