Cannot connect Host Mac to Target with Thunderbolt 3 cable

Started Target Disc [Mojave]  by holding ’T’ key until Thundebolt icon appears.  Started 2 Finder windows on Host [Mojave], cannot locate Target machine - both Finder windows the same.  Host connected to Target with Thunderbolt 3 cable

I have 2 Mojave Mac Mini: Host late 2012, Target late 2004
MARSPATHRetired EE/Computers/ITAsked:
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Are you sure you're using a Thunderbolt 3 cable?  It uses the same connector as a USB-C cable, but the USB-C cable can't handle Thunderbolt traffic.  If it is a Thunderbolt 3 cable, check the the ports don't have something obstructing it.  The charger cable that came with a Mac will be Thunderbolt 3.

However, your description indicates the years prior to the arrival of Thunderbolt 3.  You need a Thunderbolt 2 cable.  It also matches the connectors for Displayport, and Displayport only carries video not Thunderbolt 2.  (I'm accounting for a possible typo for late 2004 to be 2014.)

If you really do mean a late 2004, you will need some sort of Firewire to Thunderbolt adapter, but it's much easier to just find and use ethernet cables.
MARSPATHRetired EE/Computers/ITAuthor Commented:
"a possible typo for late 2004 to be 2014"... yes, a typo 2014 is correct.

I am using Thunderbolt 3 cable from StarTech/Amazon - 

My understanding is a Thunderbolt 3 cable supports earlier hosts.

...Are you sure you're using a Thunderbolt 3 cable?
 I believe so, installed between  both Mac Mini with no difficulties.
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