Sianturi was elected as the Regent of Sintang in a parliamentary election held by the local council on 14 March 1989. In the election, Bonar obtained 25 out of the 34 votes cast, defeating the two other candidates. He was installed on 27 March by the governor. Sianturi also initiated road repairs and the construction of a connecting bridge between the Tebelian and
Nanga Pinoh subdistrict. He commissioned the Eva Kalbar company for the project, but the company failed to finish the project in a timely manner. He later transferred the project to a different company and allocated a budget of three billion rupiahs for the completion of the project. Towards the end of Sianturi's term, the government nominated
Dayak bureaucrat L.H. Kadir to replace Sianturi, and put forward the
Malay Abdillah Kamarullah and Abdul Hadi Karsoem as puppet candidates in the elections. Unexpectedly, Abdillah Kamarullah won the election, angering Dayak politicians inside the council. Dayak politicians lobbied the central government to use their veto powers to cancel the election results, but to no avail. On the other side, the Malays consider the election of Kamarullah as fair and lauded the council for electing a popular candidate instead of a pre-determined government candidate. As a result of this dispute, the government briefly extended Sianturi's term in order to ease tensions between the supporters of Kamarullah and Kadir. Sianturi was officially replaced by Kamarullah on 5 April 1994. == Later life ==