Do you have another vehicle you can test with? You don't need to install just to check the servo. Maybe the BEC isn't strong enough in your current electronics.
What is a bec? And what does it look like because I have the 2in1 and ill need a bec.
And I'm looking at them on amazon, but I see where one plugs into the channels on the receiver but what are the negative and positive leads coming off the bec?
I guess it replaces the 2 in 1 esc and reciever? Does that mean ill need a receiver too?
The thing is, that servo draws a lot of amps. The stock esc doesn’t have a good enough built in bec to provide the correct voltage or amps to the servo. I would get something like this as it would work the best as it is a name brand.
The black wire and red wire go to battery voltage. Usually it's soldered in on the ESC's battery lead (plug).
This needs to be wired in along with keeping your ESC and receiver. I don't know anything about the 2in1 esc and receiver. If I was to wire in a separate BEC it would be in an ESC bypass configuration.
Also if you get the Castle BEC you will need a castle link to adjust it. It comes preset at 5volts. Not sure if that will affect the 2in1 Firma setup you have if you don't do the bypass.
To remove the red wire from the ESC's JR connector, use a small pick and push the little tab down gently til the red terminal pulls out of the connector. Then just fold the red wire back and tape it to the cable. If you ever need to reinsert it back into the connector, gently pry that little tab back up and push it back in.
Alternately, you could pudh the wire in and pry up the plastic tab on the connector housing that is locking that terminal in there. Then pull the terminal out.
And get yourself a servo tester
DIYmall HJ Digital RC Servo Tester ESC Consistency Tester Speed Controller for RC Helicopter Airplane Car Motor Throttle Display https://a.co/d/fKZAsGj
Did you test the radio signal with a known good servo?
Did you accidently turned down the radio's steering dual rate?
The servo will only draw max amperage when there is a load on it. I highly doubt having the wheels and tires off the ground would overload a speed control's 3A BEC.