Battery Light

That's not what the battery light is telling you. It's telling you that the battery is not being recharged by the truck. You need to have the charging system checked. It's usually a bad alternator but could be other things too. this guide can help fix it

https://www.2carpros.com/articles/how-to-check-a-car-alternator

Please run down this guide and report back.

TEST C
Ensure good connection at generator 3-pin electrical connector. Repair as necessary and check system operation. If connection is okay, go to next step.
With engine at 2000 RPM, measure voltage between generator terminal B+, Black/Orange wire (Yellow/White wire on F250 Super-Duty and F350 Pickups) and ground. See Fig. 1 . If voltage is less than 16 volts, go to next step. If voltage is 16 volts or more, go to TEST G .
With engine running at 2000 RPM, measure voltage between generator 1-pin connector terminal "S" (White/Black wire) and ground. See Fig. 1 . If voltage is 5 volts or greater, go to next step. If voltage is less than 5 volts, replace voltage regulator. See VOLTAGE REGULATOR under REMOVAL & INSTALLATION.
Turn ignition off. Disconnect generator 1-pin connector terminal "S" (White/Black wire). See Fig. 1 . Start vehicle. With engine running, measure voltage between generator terminal "S" and ground. If voltage is 5 volts or greater, repair White/Black wire between generator 1-pin connector and generator 3-pin connector. See WIRING DIAGRAMS . If voltage is less than 5 volts, replace generator. See GENERATOR under REMOVAL & INSTALLATION.

TEST G
Turn ignition to run and measure voltage drop in voltage sensing circuit "A" by connecting voltmeter positive lead to battery positive terminal. Connect voltmeter negative lead to generator terminal "A" screw. See Fig. 3 . If voltage is less than .5 volt, go to next step. If voltage is .5 volt or greater, voltage drop is excessive. Repair circuit "A" and check system operation. See WIRING DIAGRAMS .
Start engine and turn off all accessories. Increase engine speed while measuring voltage between battery terminals. If battery voltage stays at or less than 15 volts, go to next step. If battery voltage increases to greater than 15 volts, go to step 6 .
Turn ignition off. Measure voltage between generator terminal "F" screw and ground. See Fig. 3 . If battery voltage is present, go to step 5 . If battery voltage is not present, go to next step.
Disconnect generator 3-pin and 1-pin connectors. Remove voltage regulator and brush holder. See VOLTAGE REGULATOR under REMOVAL & INSTALLATION. Measure resistance between each generator slip ring and ground. See Fig. 4 . If resistance is greater than 1000 ohms between both slip rings and ground, replace voltage regulator. If resistance between one or both slip rings and ground is less than 1000 ohms, replace generator. See GENERATOR under REMOVAL & INSTALLATION.
Start engine. Measure battery voltage and observe charge indicator while increasing engine speed. If battery voltage increases to greater than 15 volts, or indicator light flickers, repair "A" or "I" circuits from generator. See WIRING DIAGRAMS . If battery voltage is 15 volts or less and indicator light does not flicker, replace generator. See GENERATOR under REMOVAL & INSTALLATION.
Measure voltage between generator terminal "F" screw and ground while increasing engine speed. If voltage increases with engine speed, replace generator. See GENERATOR under REMOVAL & INSTALLATION. If voltage does not increase with engine speed, replace voltage regulator. See VOLTAGE REGULATOR under REMOVAL & INSTALLATION.

Hi entaylor4 and TY for the donation and Merry Christmas

Check fuse no. 11 20amp and fuse no. 30 30amp

Battery light coming on means a problem within the charging system-could be the alternator not putting out or the battery is not taking it-Double check wiring/connections if okay get the alternator load tested.

Check the fusible link off of erlay to battery, there are two an dthey are a rd wire that goes to gray wires. If one I sburnt it won't charge. They ae available at auto parts stores.

This sounds like ground problems that I see pretty regularly on F-150 trucks. Remove the left and right kick panels and remove the 8mm bolts from the grounds and inspect. I’ve had lots of rust issues in these areas. Also check to make sure the ground at the passenger side frame is attached and tight, I see these left loose when engines are replaced. Another thing to try is attach a jumper cable from the battery negative to a clean spot on the chassis and drive it to see if the problem goes away. Hope this helps.

My pleasure, let us know what you find.

Check for a blown 15 amp fuse under the hood. If it's okay, measure the voltages on the wires and tell me the wire colors and the values you get. We already have one valuable clue when the battery light circuit is working. That's the "turn-on" circuit for the voltage regulator.

The voltage on the white wire has to be measured when the engine is running.

Alternator Light Stays On With Engine Running

Loose or worn alternator drive belt. Check alternator drive tension and condition,

Loose alternator wiring connections. Check all charging system connections

Short in alternator light wiring. Check wiring

Defective alternator stator or diodes. See Bench Tests in ALTERNATOR article
Defective regulator. See Regulator Check in ALTERNATOR article

Ground "B" are most of your grounds for this vehicle including pcm and trans. Unless you have the 165 amp Leece Neville alternator that is how yours is wired. Check the things I've pointed out in pic the grn wires off of starter are fusible links you have one that is either burnt, not connected or is partially making contact. Twirl them around as you check them if they break contact replace it especially how old they are. Also I am assuming that you hooked up all the sensors to the new engine. Make sure you have a ground from battery to engine and engine to body as well as battery to body and they all make contact. If you did the trans and problems started after that check for pinched harness or wire.

The flickering of power may be just to abad connection like the junction block at firewall, etc. You might try running a ground wire form engine to body or battery to body. I've sent a pic of ground locations that says where they are. Try the one on cowls and cross members. Cowl Is part in front of windshield