strange behavior with 2 Legacy locomotives

A question.

Are either of those two locomotives affected by ANY other TMCC or Legacy locomotive, and do they affect ANY other TMCC or Legacy locomotive?

John, by themselves each locomotive plays fine with everybody else.  It is only when they are both powered and get near each other.

do the have the same number in the legacy system?

The getting near each other loses me, that implies that one or both are actually radiating some sort of EMI.  I seriously doubt I could figure this out without having both of them in front of me and some test equipment.

John, I have been fooling around with both locomotives since 6:30 this morning and I think I've got it.  Running the SD70 on the outer loop with the GG1 stopped but addressed on the inner loop had no effect on either loco.  With SD70 stopped but addressed running the GG1 had no effect until a curve (072 Fastrack) where the front truck assembly turned to the right.  At that point the headlight flickered, the SD70 horn blew and became unresponsive to the controller.  I reset everything, removed the GG1 shell and ran just the chassis.  Everything work fine with no anomalies even when I ran it through an 060 crossover.

Looking at the shell, the are a number of grab irons and ladders that protrude through the shell an into the chassis area.  I flattened these down and put a 3/8 band of kapton tape around the inside bottom of the shell.  Reassembled, I repeated my tests and everything is working, even when the GG1 goes through the 060 crossover.

It seems that, for whatever reason, only the SD70 is sensitive enough to be disturbed.

Thanks for trying to help, I really appreciate it.

Very interesting, thanks for posting the cure.  That's pretty interesting, I wonder what exactly was happening.

My thought is that one of the ladder studs was able to touch the chassis but, because they are both painted, the contact was poor and intermittent causing interference in the signal.  I can see that causing the GG1 to have an issue; the SD70's sensitivity was a red herring.

I am not sure how they were contacting.  The engineering on the truck assembly seems good and I could not see any point where turning the truck could contact the shell.

In conclusion, while the problem is fixed, I can't definitively say what was touching what.

It's a mystery!

I finally got back to this.  Maybe it is not such a mystery after all but, rather, two coincidental issues.  The GG1 had some insulation issues which I corrected with kapton tape. After surgery, the GG1 is working as it should.  I removed the GG1 from the layout and ran the SD70.  It seemed to be fine but after 2 laps the horn blew once and it suddenly stopped.  It was unresponsive to the controller and could not be reset.  After about 1/2 hour, it accepted commands again but not for long.  The real problem - the RCMC board. A new one is on the way from Lionel.  I let you know how that goes.