Problem transferring data from older Mac using Target mode

Okay if the old computer won't boot, the BEST solution for you is to remove the HD from the old computer. Then put that drive into an enclosure ( OWC Mercury Elite Pro ) and then connect that drive to the new Mac using a USB cable (you will likely need a USB A - C adapter ($10 for 2 on Amazon) and then run Migration Assistant and migrate that way. You can also copy and paste the stuff you want but I'd use MA and then after the migration is complete, go back and get rid of the stuff you don't want.

You mentioned the old computer is a circa 2007, here is a link to the instructions for removing the HD from the 2007. This is for a 24" 2007, if you have a 20" 2007 then it's very similar.

https://eshop.macsales.com/installvideos/imac_24_0708e09_hd/iMac7-1-24/

Well you are certainly doing it the hard way. Please read the instructions below to learn how to migrate quickly, reliably and easily.

When you buy a new Mac the easiest, quickest and most reliable method to migrate from the old Mac to the new Mac is to simply connect the old Mac's Time Machine External Hard Disk to the new Mac using a USB cable before you turn on the new Mac. You will likely need a USB A to USB C adapter, you can find them on Amazon for $10 or less. When you start the new Mac for the first time it will startup Setup Assistant (SA), SA will get to a point where it asks if you are migrating from another computer, select Yes  and follow the on-screen prompts and it's done! It is THAT simple.

If you have already done SA on the new computer then simply connect the Time Machine External Hard Disk using a USB cable and launch Migration Assistant (MA) which is located in Applications - Utilities - MA. Then follow the on-screen prompts. 

The ONLY difference between MA and SA is MA will create a new user account that you need to log into.

Both SA and MA migrate applications (not 32 bit apps), data files & settings. They do not migrate Mac OS itself. Some professional apps such as Adobe and Microsoft apps may require re-installing their apps as they will not allow them to be migrated. As long as you kept the security keys for installing their apps, it is not an issue. 

Finally, never EVER use Wi-Fi when doing Setup Assistant or Migration Assistant. Why, it simply fails in most cases. Please read and follow the directions in Setup Assistant and Migration Assistant. If you do not have a Time Machine backup of the older Mac then create one! If you are not aware of Time Machine, please read Back up your Mac with Time Machine and finally if you need an External Hard Disk to use as a Time Machine External Hard Disk then many experience users on these forums prefer the OWC Mercury Elite Pro due to it's reasonable price, high level of quality and ease of use. 

Is this adapter a pair of adapters? An Apple Thunderbolt 3-to-2 adapter daisy-chained with an Apple Thunderbolt to Firewire adapter? Or an Apple Thunderbolt 3-to-2 adapter daisy-chained with an old dock or Apple Thunderbolt Display that has Firewire?

Beware any product that claims to be a USB-A to Firewire adapter. Such adapters are frauds. At best, they do not work, and at worst they connect incompatible power pins in a way that could damage your equipment.

The FireWire to USB-A adapter is almost certainly a fraudulent product, and, as I said before, one that may be hazardous to your computer and/or FireWire equipment. You can't adapt USB-A to FireWire.

There are some very specialized "USB-A to FireWire" adapters that are not frauds … but are meant for use as a part of a system involving very expensive, industrial-grade, laboratory test equipment. The test equipment has, say, a "USB" port that can be configured to send out USB or FireWire signals. All of the heavy lifting to "adapt" signals takes place in the expensive test equipment, and the "USB-A to FireWire" adapter merely takes FireWire signals (placed in a very NON-standard way on USB pins) and puts them on standard FireWire pins.

If you take a "USB-A to FireWire" connector meant for such test equipment and try to use it with anything else, you'll run into the same issue that you CAN"T adapt USB-A to FireWire and that attempting to do so may cause harm to your equipment. But those particular "adapters" aren't frauds … as long as they are used solely in the extremely narrow context for which they were originally designed and sold.

If I were you, I'd stop using the USB-A to FireWire adapter immediately, and hope that it had not already caused harm to my equipment.

professarap wrote:

If using a different single adapter would solve this issue, I'd be glad to try it -- any advice as to brand/manufacturer would also be appreciated in that case.

Unfortunately, there is no single adapter. Apple never made an updated version of the Thunderbolt to FireWire adapter that would plug directly into a Thunderbolt 3 port.

I agree with rkaufmann87 that you are doing things the hard way. Someone who has an old MiniDV or Digital8 camcorder, or old pro audio gear that uses FireWire, might be stuck having to shell out for daisy-chained Apple adapters – if they can still find the FireWire one.

For migration, it's easier to make a Time Machine or bootable clone (Carbon Copy Cloner, SuperDuper!) backup, of your old system, on an external drive with a USB interface, then migrate from that drive.

Please create Time Machine backup of the old computer, you can ALWAYS re-use the External Hard Disk when your migration is completed. Please read the instructions I provided for migrating, the way you are trying to do things is you are stuck in a corner.

Your welcome. If you buy the enclosure with a HD installed, then remove that drive (takes all of about 1-2 minutes) and put the 2007's into it. Once you have completed migrating then put the HD that shipped with the enclosure back in and you can use it as a Time Machine or Bootable Backup HD. If you already use Time Machine or a Bootable Backup then simply use it for overflow storage for your Photos, Music, and/or Movie libraries.

Do you have a bootable external drive (e.g., clone backup) you could start up from?

Yes, this one:

https://eshop.macsales.com/item/OWC/ME3NH7T00/