Taillight problems

JOHN GUSTAFSON

MEMBER
2004 FORD F-250
6.0L
V8
TURBO
4WD
AUTOMATIC
204,000 MILES

Tail lights do not work. Checked bulbs, checked fuses, when the bulbs are in the brake light on back of cab comes on. When I take the tail light bulbs out of both sides the brake light goes out on the bake of cab it works normal. Bulbs in light on the back of cab is on, bulbs out the light works normal. When the bulbs are in turn signal on either side both lights blink including the brake light on back of cab. I have three maker lights mounted under tailgate the lights are on when bulbs are out, put bulbs in the three marker lights go out. Checked bulbs in front both sides and they look good. The lights work fine in the front and dash lights work fine. Any suggestions? John.

Saturday, February 10th, 2018 AT 7:02 PM

1 Reply

CARADIODOC

MECHANIC
34,330 POSTS

When a group of lights work, but at the wrong times or in the wrong combinations, it is almost always due to broken shared ground wire. If lights were added with Scotch-Lok connectors, corroded splices will occur. It is just a matter of when. Those do not seal out moisture. Trailer wiring harnesses cause the same problem. All of those splices must be soldered, then sealed with heat-shrink tubing with hot-melt glue inside.

The additional clue is one bulb will be lit up, but it will go off when a different bulb, (usually on the other side), is removed. When the ground circuit is okay, no bulb's operation will be affected by any other bulb, meaning removing it from its socket, or when turning it on and off.

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Saturday, February 10th, 2018 AT 7:37 PM