I am having a problem with my Turn / Brake Lights. Just Purchased Saturday 2005 F150 4door 4x4. at 1st the only blinker that worked properly was Right Front, and both rears would lightly flash if right blinker was on, and Tail Lights Extremely Dim. No brake or Turn signals to speak of in the rear the dash would slow blink normal but when you applied the brakes they stop flashing on the dash (and the Relay Stopped), and if you use the turn signal the cruise control stops.

Things i have Tried
Step 1 Replaced all 4 Turn Signal Bulbs..... No Change
Step 2 Cleaned Battery Terminals, is a brand new battery, but did it to double check..... No Change
Step 3 Cleaned all of the Ground Wire i could find. (1 Under Hood under passenger windshield Wiper, 2 Near Battery on Passenger Inner Fender, 3 Drivers Inner Fender) Left Front Blinker now Working all other probs. still present.
Step 4 Replaced Multi Function Switch on Column. Now rear blinkers working, very dimly, and if step on brake, brake light very dim, and if on brakes the Blinker begins to Rapid Flash.

side note 3rd brake operating normally

I have seen on here about the column wires being too short and messing with the plug. should i chase that, or ground? since the ground seemed to fix drivers front flasher?
if a ground is there a reliable source for an electrical manual that shows all the proper ground locations? Or would i be better off splicing into the ground with a new ground location, hopefully back feeding the ground

 

I would get a DMM and check the resistance on light grounding pins to chassis. I would start there as a reference. It would take a few minutes to check. Ideally you want continuity (0.2 or less ohms).

If all checks out, then its a problem on the positive. Which could mean a wiring harness or connector that has corrosion, or a board problem.

 

Thanks i will check that out tonight,

 

You have a bad ground for the rear lighting circuit.

On this era of F150, that ground runs back through the body/frame harness and fastens to the body behind the LH A-pillar. Pull that kick panel cover and inspect the ground(s) there first. If it checks out, you'll need to run the harness from the rear to the front (it runs along the left frame rail), pulling each connector apart and inspecting for corrosion or other concerns. If nothing is identified by visual inspection, it will get harder.

As G303 is used for many electrical functions, none of which have been reported to have issues, it's probably okay. You'll likely find your problem in that wiring harness or its connectors.

 

I had a few min at lunch,

I checked the 2 Grounds behind the drivers Kick Panel, and the 1 behind the passenger Kick Panel cleaned and reattached (all looked good before cleaning)

then i checked the resistance, Grounded the wire to a scratch on the bed floor, Lights off, flashers offI also Checked Voltage thru the ground on the plugI [size=13px]didn't[/size] have anyone with me to check the brake voltage

i could be totally off on this thought but,i did not have time to crawl underneath to look for connections but that is what im going to check next to see if i can isolate wires.

 

None of that makes any sense and that's coming from an electrical/electronics tech with four and a half decades of experience in the field.

Rule #1. NEVER make resistance checks in a circuit that has (or may have) power applied to it. You will get either wrong readings or a fried meter. Or both.
Rule #2. When making voltage readings - Unless advised to do otherwise, ALWAYS connect the negative meter lead to a KNOWN GOOD ground connection.

Additional advice:

1. Always fully describe what/where/conditions you're making readings at/from.
2. Since the corner stop lamps are also used as your hazards, you can engage your hazards and look for a pulsating voltage to the stop lamp circuit for the corners.

 

Update,

1. i verified the location where i was pulling ground from, with a jumper from the positive battery post, and had 12.7V there.
2. I verified no voltage was going to the wires at the back of the plug, with needle tip probes on a Fluke 87V
3. i double checked the ohms with all the lights off, (Lights were off 1st time but did not verify lack of voltage) and had similar readings to the 1st attempt,
   1. Ground Wire No Continuity about 140 Ohms
   2. Brown Wire Showed Continuity
   3. Lt Green/Orange Showed Continuity
4. Checked Voltage on back of plug
   1. with Parking Lights on, Measured from back of plug 7.4 V
   2. with Flashers on 12.7V. on the Flash (High Side) Low When off was hard to tell, but would fall to about 5.3 before jumping back up again.
   3. Ground was 0V with either
5. Checked Voltage on the bulb connectors
   1. Parking Lights 3.6V
   2. Flashers 7.2V
   3. Ground not 0V but less than 1V

So the issue may be in the plug itself

 

I use items like sanded paper clips to stick into those connectors then use my meter with alligators to ensure I get a good connection.

It sounds lame, but it works and it doesn't damage the connector (as long as you don't ram it in it!).

 

When you are testing ground wires to the chassis is the battery disconnected? It needs to be or you can get false readings.

Like was suggested by ManulF150, I would start by disconnecting the rear parking light connectors at the bulbs, then testing the ohms from each ground wire (i.e. the wire side of the connector) to a known good ground.

Let us know the results so we can work with you to resolve these issues.