Thank you for your comments, in response:
PS-2 upgrade on a SS 4-8-4. Previously working fine for quite a few total hours. Has been run on medium to slow speed on a regular basis. Beautiful brass beast and a great puller.
Controller works fine for other PS-2 upgrades and factory PS-2 & factory PS-3 locos steam and Diesel.
Tether is fully engaged and the cord appears intact.
Only ever used in conventional.