Turn signal failure

[qmcdugan]

Light wise, the important stuff is working. The biggest issue is the left rear turn signal. It worked a couple of weeks ago.
The large housing screws were rusted in-place and it took using my hand impact driver to loosen and get them out. In reading the note left on another thread, indicates, rear turn signals ground through the screws. So, some more cleaning is in order. Pulled the housings from the body and unplugged the light.

With ignition, park lights on, and left turn signal engaged. The front left turn signal is flashing but a little slower then the right side. Tested the two connections. The female #285 brown is the tail light (good) and the male #283 ylw/blk is the turn signal (nothing). Check the right side, both are good.

The sockets of both tail lights are in bad shape and I'm in the process of getting housings and new lenses, but that of course won't address the no flash @ the left rear.

Question: Might there be a place, that a break would more likely occur than another? A short would blow the fuse, would it not?

[basketcase0302]

"qmcdugan"]Light wise, the important stuff is working. The biggest issue is the left rear turn signal. It worked a couple of weeks ago.
The large housing screws were rusted in-place and it took using my hand impact driver to loosen and get them out. In reading the note left on another thread, indicates, rear turn signals ground through the screws. So, some more cleaning is in order. Pulled the housings from the body and unplugged the light.
With ignition, park lights on, and left turn signal engaged. The front left turn signal is flashing but a little slower then the right side. Tested the two connections. The female #285 brown is the tail light (good) and the male #283 ylw/blk is the turn signal (nothing). Check the right side, both are good.
The sockets of both tail lights are in bad shape and I'm in the process of getting housings and new lenses, but that of course won't address the no flash @ the left rear.
Question: Might there be a place, that a break would more likely occur than another? A short would blow the fuse, would it not?

A short can be indirectly or partially grounding drawing current away from the circuit and still not be a "dead short" (directly to ground). From your description of the screws I'd first start with running a dedicated ground to the back of the truck from the battery / PS inner fender where you know there is a good ground, (you can also test this troubleshooting by hooking up the ground temporarily). You can also test the circuit for power up by the cab, (believe it's a four wire harness that leads down the firewall by the steering column heading aft).
And hate to be the "bearer of bad news" but most of the time the turn signal issues that aren't ground problems lead back to the turn signal switch, (which really isn't too hard to replace once you've done one).

Hope it helps.

[qmcdugan]

Last month I added an additional ground cable from the engine block to the fire wall. I have also cleaned the other ground points, ie the little pig-tail from the Neg terminal to ground, the negative battery cable to the block etc. If I understand your meaning (PS) = passenger side, wheel well needs a ground ?
Turn signal switch was replaced in 08, but that may yet prove to be the problem. I need to get under the box and clean. Then using my pointed test light and (a little clear finger-nail polish to seal the pin holes I make), start working my way forward till the test light illuminates. Not fun but I don't know what else to do. Thanks for the quick response. Mike

[basketcase0302]

Didn't realize you'd already added the ground-so you've eliminated a ground issue if you have a "dedicated ground wire" ran from the front of the truck back to the rear of the bed, (if you can hook that wire to the left housing and it changes nothing). I absolutely hate those test lights that pierce the insulation as ultimately I've seen hundreds of trucks here over the years with wiring issues where the wire has broken down-that being the culprit.
But if you don't have a voltage meter, ($5 at harbor freight) you have to "make lemonade out of lemons".
The location I was referring to is where your wire #283 yellow black tracer leaves the cab and heads toward the back of the truck (wire #GG267 in the image below). I believe there is a four wire harness very close to the steering column you can unhook and test for power there-as I don't think that wire has another connector before it reaches the tail light lens, (that you could test without piercing the wire). The wiring on these trucks was almost all copper from the start and pretty tough-one of the last issues you'll have with electrical gremlins on the truck.
And there is one more ground i did not see you mention. Our bumps came with a ground "strap" (was a flat braided cable) from the factory that connected the rear of the engine head or intake manifold to the firewall, (a lot of times guys have yanked this one off changing engines or working on the engine)-make sure the engine to firewall ground is intact.



The steering column should also have a ground from the column to the frame something like this (but usually a lot smaller from the factory):

[fordman]

The most common place to fail. Is the turn signal switch or the wiring under the column going to the turn signal switch.