Hey all, I have a 2002 F150 with the 5.4 V8.
When I got the truck a few months ago the turn signals were working, but now they've stopped.
The hazards still working, all of the other lights (brake lights, backup lights, hi/low beams, etc) are also working, it's only the turn signals that don't seem to work.

Repairs attempted:
I've tried clicking the hazards on and off repeatedly, to clear the contacts, no effect. I tried raising the steering all the way, also to no effect.
I've already replaced the flasher relay and the fuse for the turn signals (actually, I pulled and replaced every fuse in the under-dash panel). I've cleaned all of the grounds that I could find. I've also pulled apart and cleaned the MFS, as I've read that the conducting grease can start to run and cause shorting issues. (Everything seemed to be working fine, and I didn't see any broken or cut wires).

I can't get it to pass inspection until I get the turn signals working, so any help would be appreciated!

A little extra information, between the turn signals working and not working, I did have a leaking windshield, which cause shorting and corrosion in the fuse panel, but I pulled it all apart and cleaned up the corrosion.
Also, the side power mirrors and dash cluster illumination are not working. May be unrelated...

 

Do you have (and know how to use) either a multimeter or a test lamp? The time for guessing is long past, it's time to actually troubleshoot the issue.

 

Thanks for the quick reply. I do have (and know how to use) a multimeter.
And yes, I am tired of guessing at the issue.

 

Additional question before digging into the circuit: Does the flasher relay click when either turn signal is selected, same as it does for the hazards (which you indicated are functional)?

 

No. I get no sound from the flasher relay with the turn signal in either direction.

 

I was going to type out a step-by-step, but I see the service manual already has what I was going to type so I attached a copy of the pertinent section and its schematic. Go through the procedure and see where it fails. Let us know if you get stuck or need an explanation.

There's an open circuit somewhere between the fuse box and the internals of the MFS via the flasher relay. Focus on the supply circuit from F23 (#294) first and then circuit #44 between the flasher relay and the MFS. Use the instructions and the road map to trace it out.

 

Ok, thanks so much. I'll check it this afternoon and let you know the results.

 

Ok, circuit #294 tested fine (11.55V), as did circuit #44 (.52ohms to MFS, OL to ground).
Circuit #383 seems to be the problem. I only got .004V from that circuit (tested 4 times, to be certain).

So, we seem to have identified the problem, but how do I fix it?

 

If circuit 383 were un-powered, your hazards would not work. You said that they do work. Therefore, the test results are suspect since they disprove a previous observation.

Did you follow the diagnostic routine (Pinpoint test K) PRECISELY, only one step at a time? If K1 failed, you should not have ended up in K2...

 

Hm, strange. I did go through the Pinpoint test one step at a time. The reason I went on to K2 was 1. Thoroughness 2. I already had the steering column cover off, so it only took me a minute to test it.
I'm certain that the hazards work, so I'll test that circuit again and see if I made a mistake testing it. Thanks again for all of your help so far.

 

Just checked again. You are, of course, correct. Circuit 383 has 11.55V, its circuit 294 that is un-powered. So, how do I fix that?

 

Step K1 said specifically "No - REPAIR the circuit in question. TEST the system for normal operation." You were to proceed to step K2 ONLY if step K1 passed (it failed).

Circuit 294 is supplied by F23 (HOT IN RUN).

Go back to the fusebox and check for power on both of the fuses's test points with the ignition switch in RUN.

If power is on one point but not the other, it's the fuse.
If power is missing from both points, it's the supply to that fuse.
If power is present on both test points, there is an open circuit between the fuse's load terminal and the connection at the flasher relay.

Given that the truck has a history of water infiltration of the fuse box, I'd focus attention there. Pay special attention for spread or corroded fuse terminals.

 

OK, I checked F23 with the truck on, and I've got power (11+V) on both test points, so it's an open circuit between the fusebox output and the flasher relay.
I can see that it's a wh/lb wire that feeds to that circuit in the flasher relay. I'm not great with wiring diagrams, but is there a way to tell whether the wire is a straight shot from the fusebox output to the flasher relay, or if there is a break (wiring harness, etc) in between?

Or would it just be easier to run a new wire from the fusebox to the flasher relay?

 

Bypassing the open would be an easy repair and get you through inspection... or forever. That's probably what I'd do if pressed for time. Pick up a fuse tap of the correct size (ATM or ATC), some wire, and, with a bit of extra work, the open should be bypassed and function restored.

Technically, we can only define it as an open between the points where you made the measurements - the load terminal of F23 and pin 30 of the flasher relay where you made the measurement. Greater precision would require a more focused set of measurements.

 

OK, thanks so much for helping me track this down. Today I pulled out the wiring harnesses from the back of the fuse box and discovered that several of the connectors were really corroded, so I pulled them out and scrubbed them clean. Now the turn signals are working again!

Having said that, I have another issue now. Now, the instrument panel is not working (I have some lights: 4x4, door ajar, ABS) but the gauges are not working. I did check the test points on the fuses, the problem is, there are 4 fuses that all include the instrument panel. Fuses 2, 6, and 30 all have 10+ volts. Fuse 16 only reads .15V, but I wasn't sure if that's what it was supposed to read. (I tested it with the headlights off and the headlights on, headlights work fine, but still no voltage at the fuse.)