legacy es44ac blinking cab lights

I had an MU with 115 cars pulled by two Legacy U28 U-Boats, and I started out very slowly, never saw any blinking lights.  AFAIK, that is not normal.

Make sure your track had good feeder wires around the grade area, as track joints can develop resistance and cause voltage droops as the current requirements change on the motors.

you beat our club record of 107 cars a few months ago.

also the op did not state what kind of track power they are using.

could be an issue.

You're pulling your consist with a Z4000?  Must have been an interesting sight!

I believe that Jon's comment doesn't address what transformer you're using, but rather the wiring and track condition.  Clearly, with the Z4000, you have sufficient power for your engines.

we have found at the club that the z4000 has a tuff time on our large layout so we recommend everyone use the two 180watt bricks we also have on the layout, for large trains.  our z4000's are over ten years old.

I will edit the above.  the z4000 have a tuff time with large trains of two or more engines and 10 or more lighted passengers cars.  we make the general statement if running in command to use the bricks and they have less issues.

Hard to believe that the Z4000 won't move an engine and 10 cars, even heavy cars!  I've moved a lot more than that with my Z4000.

After Jons comment on the track power lockons, I have cleaned the track and also put 19 volts to the track with the z4000. Ater doing this with one of the Es44ac's I couldn't get it to stall out. I thought the track was clean, but I guess it can always be cleaner. I haven't got around to checking the other loco.

 Keep in mind I am using the cab 1 and get the loco to literally crawl around a 24 x 12 oval with 82 curves. It takes over what seems to be 15 minutes to make a lap. Amps show low on the z4000. I am hoping that the semi dirty track is the issue. I am curious if anyone out there has ever stalled a consist with only using 1 legacy loco.

I don't find it surprising that dirty track causes the issue.  Of course, I'd also clean the wheels and rollers to complete the job.  Poor connections anywhere in the chain will indeed cause all sorts of operational issues.