Adhesion promoter compositions, containing: a) between 40 and 80 parts by weight of a binder composition, including i) 20-40 wt % of at least one silane-terminated polyurethane polymer STP, which can be obtained from at least one polyol P, aliphatic polyisocyanate I and organosilane OS1, ii) 4-20 wt % of at least one organosilane OS2 and/or organotitanate OT, iii) 0-3 wt % of at least one desiccant, iv) 40-80 wt % of solvent L1; b) between 0-30 parts by weight of industrial carbon black; c) between 0-1 parts by weight of UV marker; d) so much of solvent L2 that sum of a)-d) is 100 parts by weight; OS1 having secondary amino, mercapto or hydroxyl group on organic moiety and the at least one STP having been produced in absence of OS2, and the at least one P having an average OH functionality of at least 2 and equivalent weight of at most 500.