The non digital Stainz and porter locos were 18 volt screw in tinted lights.  The newest (Marklin/MTS) digital units would most likely be 5 volts.

If the 6 digit gold sticker is still on the bottom of the engine then the first and last digit is the year.

split case would be before mid 90's.

Rear light is secured by a screw located behind the white reflector.  And this screw attaches the fixtures on the rear of the cab.

Disassembly:

https://shop.waltonsmodels.co.uk/Stainz.php

I bought a used one, and will convert to DCC. I found some links for conversions:

https://riksrailway.blogspot.com/2016/03/how-i-converted-lgb-stainz-loco-to.html

https://riksrailway.blogspot.co.uk/2008/06/how-did-i-install-decoder-in-my-stainz.html