In the study of third language (L3) acquisition, it has been recently been suggested that patterns of crosslinguistic influence (CLI) may differ for, e.g., syntax as compared to phonology, with the latter being more dynamically affected by changes in the learner’s environment (Kopečková, Marecka, Wrembel, & Gut, 2016). However, since most L3 studies to date have investigated CLI within a single language domain, there is a call for studies that systematically assess CLI across multiple modules of the grammar within the same population of speakers (Rothman, González Alonso & Puig-Mayenco, 2019, p. 256). The present study examines the acquisition of L3 English across two domains, namely perceived global accent (phonetics-phonology) and acceptability judgements (syntax). The participants are 21 German-dominant heritage speakers (HSs) of Italian, with two control groups of L1 Italian and L1 German speakers (N=31). The effect of HL use on CLI into English was controlled for using an extensive background questionnaire. The results from the accent rating study indicated that, while most of the bilingual speakers were rated as German-sounding (no statistical difference to L1 German controls), an influence from Italian was detected in one third of speakers. In regression analyses, the number of ‘Italian-like’ ratings was predicted by ‘Italian Use’. In the AJT, the bilinguals accepted embedded wh-questions following the Italian linear word order significantly more often than L1 German controls did (interpreted as CLI from Italian), but also accepted stimuli following the German word order, suggesting simultaneous CLI from both sources. Interestingly, while ‘Italian Use’ predicted an Italian-sounding accent, it did not predict syntactic CLI from Italian. The results speak for the equal availability of both systems for L3, with L3 accent being more affected by dominance patterns and HL use than syntax is.