How to go from dual boot to triple boot sierra+windows+mojave?

[MPG951]

I currently have Sierra + Windows on separate SSD drives since 2016. What would be the process for installing Mojave on a third internal SSD. I tried installing mojave to an external SSD but I could not finish the install process as the bootloader does not show the Mojave SSD after restarting even though it seemed to be installing and I believe the EFI for the Mojave SSD is empty after mounting it on Sierra. Tried this method on other macbook and mojave installed on the external SSD & booted. What gives.

 

[Going Bald]

What file format is the Mojave drive? HFS+ or APFS? If APFS, you will need to update Clover on the Sierra drive or install Clover on the Mojave drive to be able to boot it.

 

[MPG951]

What file format is the Mojave drive? HFS+ or APFS? If APFS, you will need to update Clover on the Sierra drive or install Clover on the Mojave drive to be able to boot it.

I would be purchasing a Crucial MX500 SSD after succeeding with the Samsung
Portable SSD T5. PS. I succeeded in getting the
Samsung
Portable SSD T5 with Mojave but could not get the Intel HD graphics to be used & recognized after following some tutorials & messing around I decided to start again. So I attempted to reinstall with Mojave USB but the computer will not recognize the Mojave USB anymore and so I can not boot from it. Any ideas.?

 

[icoric]

Have you managed to accomplish this?

 

[MPG951]

Not yet but about to clone Main drive to Samsung SSD 860 EVO and then attempt a Mojave update on the clone. First have to pickup the SSD from Best buy.