No, not all M104's have the harness problem. Only the one's with what has been called EFI on this post, more technically would be referred to as SFI, or Sequential fuel injection. The earlier versions, KE or CSI-E (same thing) didn't have a wire that connected to each individual injector. The CIS-E versions used an injection set-up much like the 103 had. When they went to the SFI injection, there was much more wiring involved due to the fact that each injector had to be connected to the control module.
The early version is easily identified by looking for the metal tubes that run from the fuel distributor to the injectors, like a M103 motor. On the later version, you can see the wire going to each injector, the injector is suppied with fuel from a large common pipe that runs over the injectors, not small individual pipes for each cylinder.
ps Another easy way IN GENERAL to tell the 2 types apart is the early version has a metal air filter housing on the drivers side of the engine, the later (troublesome harness) engine has the air filter in a square plastic box on the passenger side of the car, behind the headlight.