Right side tail light and marker light not working

[hath]

Hi guys,

I've got a 70 f100 swb 2wd and the other day my right side tail light and marker light stopped working. Everything works on the left side, and everything but the tail light and marker light are working on the rights side, i.e., blinker, brake, and reverse light. What would you suggest?

[HIO Silver]

I suggest doing some troubleshooting like checking grounds, voltage, and bulb sockets, and whether both bulbs could be blown.

[hath]

So I went around and fixed some grounds that looked rather corroded. I've switched bulbs but that didn't fix it, besides the marker light doesn't work either so I feel there's some underlying issue. I figure the marker and tail light work off the same current.

[sargentrs]

Does your turn signal work? How about the front marker and turn signal? Inspect your rear harness and make a jumper at the plug for your left to power your right to test the harness and tail light assembly on that side. Test your power at the connectors in the rear harness. That will narrow it down. Here's a diagram to help you find the connections. http://www.fordification.com/tech/wirin ... odel99.jpg

[hath]

The turn signal works and everything on the front of the truck is working. I'll test the harness like you're saying. I did find what appears to be a stock connection right before the wires go to the left tail light (the harness goes to the left tail light, and from there to the right), the connector is what i'd call a 3-way connector because it has three wires into it and three wires out, but when I test each one, there's only power to one of them, I'd assume there'd be two hots and one ground in that situation, but I"m not sure. This may explain why the left side works but not the right side?

[sargentrs]

Right connector, circuits a little different than you think. The ground is through the light socket to the housing to the bed, through the screws. Check out this diagram http://www.fordification.com/tech/wirin ... odel99.jpg Here's a snip of the connector connection. Hopefully, I'm reading this right, sometimes I get confused. The power comes in on wire 285 (brown) from the headlight switch which is the 2 prong connector next to the 3 prong connector. From there it goes to the center pin of the 3 prong connector. From there, wire 282 (green) goes to the passenger lights, wire 283 (yellow/black) goes the driver side lights. Wire 140 is your back up lights. From the center pin of the 3 prong connector, wire 285 goes to both lights through the corresponding 2 pin connectors (285A and 285B). With the lights on, you should have power to all three prongs of the 3 prong connector to one of the filaments of the tail light bulbs. Wire 282 and 283 are your tail lights, 285A and 285B are your turn signals which double as your brake lights. If not, back up to the 2 prong connector and check it there. If either of those has no power, suspect a bad ground at the bulb socket or where the housing screws into the bed. I had one once that gave me fits. Turned out the dimples inside of the bulb socket were corroded. Some steel wool on a screwdriver cleaned it up and they worked fine after that.

[hath]

That's exactly what I needed, I'll go tinker on it tomorrow to see what I can figure out. I don't think I'll need to go any further back than that 3 way connector. While working on it I did realize that the tail light housing is grounded via the screws, so I took my dremel and ground down all the contact areas to make sure I was getting a good ground.

If I'm hearing this right, when the headlights are on, the only prong having power on the 3 way connector will be the center one? That's how it is already, so that narrows things down quite a bit.

[hath]

I need to clarify a little. When I said I figured out that the lights work via the tail light housing being grounded to the body, it was by accident I figured it out. I had the housing dangling there and I saw it sparking a little as it touched the bumper, when I touched the housing on bare metal (giving it a good contact), the lights would light up. In this case it was the brake lights.

My question is, should that housing be sparking when it is loosely touching bare metal? Now thinking about it, that might not be a good thing, it's kind of acting like the housing is energized?

[sargentrs]

If I'm hearing this right, when the headlights are on, the only prong having power on the 3 way connector will be the center one? That's how it is already, so that narrows things down quite a bit.

That is correct. The bottom one in the drawing is the back up lamp and the top one is the passenger side turn signal.

[sargentrs]

My question is, should that housing be sparking when it is loosely touching bare metal? Now thinking about it, that might not be a good thing, it's kind of acting like the housing is energized?

That's normal. The grounding through the housing is completing circuit. If it didn't spark, I'd suspect a weak power connection.

[hath]

I got it figured out. There was a short in the harness (in a stock splice) between the two tail lights. Thanks for your help everyone!

[sargentrs]

Glad you got her working.