I have a 2005 f350 6.0, my left rear stop signal is not working. I have changed the relay. I only get 5-6 volts at the plug and green-orange wire all the way to the engine bay. Not sure what the problem is

 

There is no relay in the basic stop/turn lamp circuit.

Under what condition did you make that voltage measurement?

Have you tried a new light bulb?

 

I switched the bulb and holder from the right side and still nothing.
To test I simply turned the signal on and tested it with a meter. 5 volts at the plug, 5 volts at relay 202 I am pretty stumped on this.

 

Sounds like it may either be your brake switch or your multi function switch.

Here's a link I found that may help;

https://www.ford-trucks.com/forums/8...t-working.html

 

Nope. That would affect BOTH brake lights.
A decent chance.

It doesn't, different symptom.

Which terminal of the relay? Yep, need to be VERY specific when reporting test results. FWIW, that relay is not used in the truck's turn/brake signal, it is used for the trailer circuit but is activated by the truck's signalling circuit. It's not part of this circuit unless you just want to use it as a test point before taking the column covers off.

Pull the covers off the column and inspect the connectors at the MFS paying particular attention to the LG/OG wire on connector C202b (12-pin connector). Check voltage on that pin by back-probing it while you have your foot on the brake. If it doesn't read battery voltage, check the OG/LB wire on the same connector (that's the rt side stop/turn lamp) as a comparison. If the right side is good (battery voltage) but the left side isn't when measured at the connector, you have a bad MFS (most likely). Check the pin seating and the condition of the suspect pins before buying a new switch.

 

I thought his brake switch had separate leads, one for each side, not one tied to both.

 

Nope. There's a single wire from the BPP switch to the MFS switch for the brake lights. The circuit gets split left/right brake/turn inside the MFS.

 

Ok so still can't fix this.
after it's first assembled it flashes 5-6 times then stops working. I can apply the brake and get 12v at the socket with a meter but a test light or bulb won't light up.

 

I still say it's a ground. If you measure 12v with a meter but no lights it has to be ground. Looking at
wiring diagram if you have a fireside bed the socket is grounded but a standard bed there should be a
terminated ground wire. I would try running a temp ground wire to the socket to see if that fixes it and if it does then you know to look for a bad ground on that side.

 

The ground tests fine and the running light works . I tried jumping the ground and it still don't work , I guess I'll try a new multi function switch and see if that helps

 

You have a high resistance in the circuit (not the ground). It could be in the MFS (Burned contact, for example) or anywhere in the wiring harness (corroded connector, for example) back to the bulb.
That's because the bulb requires far more current than does a voltmeter. A high impedance digital meter requires almost not current at all (a few microamps, perhaps) while the bulb may require several hundred milliamps or more.

Did you ever follow the explicit directions I gave you almost a month ago to measure at the MFS?

 

Ok fixed it was the multi function switch.
Thanks for all the help!
oh no not working again. I am going to try running a new wire from front to back.
I tested battery voltage then gr-bl vs og-br with the brake applied at the mfs and it's good, at the rear connecter by the bumper the left side is down slightly 12.4 vs 11.89. I am assuming that's a problem
Project089 thanks for the advice