If the glider was built in Germany there's probably also a TN from the manufacturer giving guidance on installing equipment. Linked as an example is the one Schleicher provides. This sort of thing could be useful if your A&P wants more than the (often very terse) glider manual and the AC 43.13 to go by.
https://www.alexander-schleicher.de/...02_E-II_HB.pdf