I want to no test something for 3 volts testing a solar cell

Taking the vehicle to ford an having the modual programmed . You can't just replace these modules . Give them the old one ,check for DTC'S - diagnostic trouble code's . Nothing you can or should do.
NOTE: Some PCM DTCs may inhibit A/C operation. If any PCM DTCs are retreived, diagnose those first. Refer to the Powertrain Control/Emissions Diagnosis (PC/ED) manual. DTC Description Action to Take B1003 Mode Door Short/Failure Go To Pinpoint Test F . B1200 Stuck Button Button held too long may set DTC. ATTEMPT to clean buttons. If code returns, INSTALL a new electronic automatic temperature control (EATC) module. REFER to Section 412-01 . B1251 In-Vehicle Temperature Sensor Open Circuit Go To Pinpoint Test A . B1253 In-Vehicle Temperature Sensor Circuit Short to Ground Go To Pinpoint Test A . B1255 Ambient Temperature Sensor Open Circuit Go To Pinpoint Test B . B1257 Ambient Temperature Sensor Circuit Short to Ground Go To Pinpoint Test B . B1342 EATC Module Faulted INSTALL a new EATC module. REFER to Section 412-01 . B1676 Battery Voltage Out of Range Go To Pinpoint Test Q . B2266 LH Blend Door Failure or Short For vehicles not equipped with electric heater, Go To Pinpoint Test K .
For vehicles equipped with electric heater, Go To Pinpoint Test L . B2267 RH Blend Door Failure or Short For vehicles not equipped with electric heater, Go To Pinpoint Test K .
For vehicles equipped with electric heater, Go To Pinpoint Test L . B2268 Steering Wheel Control Switch Circuit Open Go To Pinpoint Test D . B2269 Steering Wheel Control Switch Circuit Short to Ground Go To Pinpoint Test D . B2426 RH A/C Solar Radiation Sensor Open Circuit Go To Pinpoint Test C . B2427 RH A/C Solar Radiation Sensor Circuit Short to Ground Go To Pinpoint Test C . B2795 LH A/C Solar Radiation Sensor Circuit Short to Ground Go To Pinpoint Test C . B2796 LH A/C Solar Radiation Sensor Open Circuit Go To Pinpoint Test C . U2050 No Application Present INSTALL a new EATC module. REFER to Section 412-01 . All Other DTCs - REFER to the Master DTC Chart in Section 419-10 .

Have it checked for DTC'S - diagnostic trouble codes .
Electronic Automatic Temperature Control (EATC) Module DTC Chart NOTE: Some PCM DTCs may inhibit air conditioning (A/C) operation. If any PCM DTCs are retrieved, diagnose those first. Refer to the Powertrain Control/Emissions Diagnosis (PC/ED) manual. DTC Description Action to Take B1251 A/C In-Vehicle Temperature Sensor Open Circuit Go To Pinpoint Test A . B1253 A/C In-Vehicle Temperature Sensor Circuit Short to Ground Go To Pinpoint Test A . B1255 A/C Ambient Temperature Sensor Open Circuit Go To Pinpoint Test B . B1257 A/C Ambient Temperature Sensor Circuit Short to Ground Go To Pinpoint Test B . B2427 RH A/C Solar Radiation Sensor Circuit Short to Ground Go To Pinpoint Test C . B2426 RH A/C Solar Radiation Sensor Open Circuit Go To Pinpoint Test C . B2795 LH A/C Solar Radiation Sensor Circuit Short to Ground Go To Pinpoint Test C . B2796 LH A/C Solar Radiation Sensor Open Circuit Go To Pinpoint Test C . B2014 Evaporator Temperature Sensor Circuit Open Go To Pinpoint Test D . B1947 Evaporator Temperature Sensor Circuit Short to Ground Go To Pinpoint Test D . B295A LH Blend Door Potentiometer Feedback Circuit Open Go To Pinpoint Test F . B295B LH Blend Door Potentiometer Feedback Short to Ground Go To Pinpoint Test F . B226C LH Blend Door Motor Stalled Go To Pinpoint Test F . B295C RH Blend Door Potentiometer Feedback Circuit Open Go To Pinpoint Test F . B295D RH Blend Door Potentiometer Feedback Short to Ground Go To Pinpoint Test F . B226D RH Blend Door Motor Stalled Go To Pinpoint Test F . B295E Mode Door Potentiometer Feedback Circuit Open Go To Pinpoint Test F . B295F Mode Door Potentiometer Feedback Short to Ground Go To Pinpoint Test F . B226E Mode Door Motor Stalled Go To Pinpoint Test F .
Need to use a professional scan tool to check these codes !

3 volts plugged in?

Even though it has a new battery , it may be a faulty battery. If it is a sealed battery test by connecting to a volt meter or if you can top up the battery fluid (distilled water) you can test with a battery hydrometer, alternatively you could use a solar battery charger plugged into cigarette lighter to maintain charge. Hope this helps

When a battery is giving 18.8 volt, the battery is defect, or your Volt (multi) meter is not calibrated or defect.
Check if all cells have enough fluid and if possible measure each cell to establish if one or more are defect.
each cell can be a little over 2 volts, but 3 or more is really not possible for a working lead acid battery.

Alternator tested 'On Vehicle' of 'Bench Tested' ??
I recommend begining with a scan,followed by our shop's standard fault tracing procedure....
INSPECT BATTERY ELECTROLYTE LEVEL
INSPECT BATTERY RESTRAINT
INSPECT BATTERY CABLES/TERMINALS
****LOAD TEST BATTERY,_______VOLTS @ 150 AMPS (Min SPEC 10.2 VOLTS @ 150 AMPS.)
TEST STARTER AMP DRAW,______AMPS INITAL,_____
AMPS SUSTAINED.
****INSPECT BELT(s),
****TEST ALTERNATOR OUTPUT,_____AMPS @ 12 VOLTS @ 2500 RPM (SPEC ______ AMPS.]
****TEST FOR DRAW,______(MAX ALLOWABLE 350 Ma),

If you need further help, reach me via phone at https://www.6ya.com/expert/ralph_2f0886b7d6af32ce

if problem is a parasite drain the following links will help
How to Find Parasitic Battery Drain How To Perform Parasitic Draw Test EricTheCarGuy How to do Parasitic Battery Drain Test

You can have a dead cell in the battery which pulls the other cells down when it is sitting. If the battery is over 3 years old, I would suspect this is your problem. You may also have something on that is draining the battery. A glove box, dome, interior, trunk, or under hood light, for example. If you remove the negative battery cable when it is fairly dark and see a spark there is something drawing power. The radio presets will draw very little power and you will see a tiny spark which is normal. If you see more than a tiny spark something else is on. I suspect you just need a new battery.

suspect the air bag light came on due to it sensing a low battery voltage which woud cause the air bag to not deploy. Check to see if your battery is carging first. It should read 12 volts with engine off. it should read 14 -15 volts with engine running.
Next check for a dead cell in battery. Need to have any auto store test it for free.
If all good, check for battery drain from something still on after key is off.