[SOLVED] Booting Mojave OS from an external HDD.(WD my Passport)

[Reak111]

I use a Macbook pro-2015 15inch model. I don't know what happened but, my SSD failed and stopped working. I tried all sorts of resets and whatnot, all the same. so, I decided to install Mojave OS on an external HDD. (WD my Passport). I installed Mojave OS successfully through an Imac that's on Mojave already because the process didn't work on El Capitan. Now,if I choose the newly loaded external HDD as the start up disk on the imac that installed it, it will boot successfully to desktop or home screen. But,if I mount it on the macbook pro,it will only boot halfway on the apple logo ,then restart. It's not booting successfully on the he macbook pro.

1. Is it wrong to put Mojave on a HDD?
2. Is my MacBook pro missing a firmware?
3. Please,else can i do?
4. I formatted the external HDD in APFS.

 

[velocityg4]

Run the hardware diagnostic there may be more wrong with the machine.
https://support.apple.com/en-us/HT202731

When Macs have a failed drive connected. I've found they have a difficult to impossible time booting. Even if that drive is not the current boot drive. I couldn't say why the OS won't just ignore the faulty drive.

Try booting to Internet Recovery.
Option-⌘-R or Shift-Option-⌘-R at boot. I believe you can also just hold the option key and select your network. If it locks up on booting internet recovery. Getting the machine to boot. At least into macOS may not be possible.

While you're at it. Try a PRAM and SMC reset.

https://support.apple.com/en-us/HT204063

Reset the SMC of your Mac - Apple Support

The SMC is responsible for managing power on your Mac. Resetting it can resolve certain uncommon issues related to power or thermal management.

support.apple.com