I just put the bed back on my truck and now the taillights don’t light up when I press the brake pedal or use my blinkers but they come on when I turn on my headlights. Would this be more likely to be the switch, plug, or am I just gonna have to get out the multimeter and run it down?

 

Yes, Yes and Yes
I like using a test light over a meter as I can see what is going on and not need to be on top of it like a meter.

Has the truck been sitting for a bit?
Check the fuses first. If it has been sitting for a bit pull the fuses and clean the ends and holders.

Then I would check power at the stop light switch.
You should have power into the switch even with out the key on.
Press the brake pedal and the other side of the switch should have power.
If not bad brake light switch.

If power in and out that goes up to the turn signal switch.
If the truck has been sitting try moving the switch a bunch and see if you have turn and brake lights out back.
If not I would then check for power at the turn signal switch plug to see if you have power in and out there.
If power in but not out bad turn switch.

If you have power out then you will need to start checking the wiring from there on back to the rear lights.
There is a rear light harness plug in the engine bay kind of under the brake master, runs along the frame rail to the tail light, can pull it apart and check for power there.
The last plug is at the vary back where the tail light harness plugs into the frame harness.

So as I said yes, yes and yes LOL
Dave ----

 

I got the brake lights to start working but just cleaning out the connector but now when I turn off the truck the brake lights stay on

 

Pull the fuses till they go out. See what number fuse makes the brake lights go out and then write back in. Make sure you tell us what year,, model, etc. you are working on.

 

Take a look at this troubleshooting guide:

https://www.ford-trucks.com/forums/1...ing-guide.html


Note the section describing the dual filaments is some of the bulbs. Look very closely at your bulbs to confirm which filament is illuminated. Under certain conditions, typically a bad ground, the other filament can light up.

The guide also shows the brake switch and how to test it. As Dave suggested, try pulling fuses one at a time to see which one was powering the lights when they are supposed to be off.

 

If it is the brake lights staying on an easy way to check is to unplug the brake light switch and see if they go out.
What connector did you clean out maybe look at it again?

With the truck off there is not much that should have power to it.
Brake lights, 4 ways and head lights if turned on.
Dave ----