This 29-page PDF is a collection of pages from AC Bulletin 3D-5, dated October 1968. It covers testing, calibration, service, repair, specifications, and troubleshooting for electronic tachometers used in 1964-1968 GM products, and also includes the tachometer part numbers.
To view the PDF in your web browser, just click the link below. To save to your computer, right-click on the link below and choose "Save As...". AC Electronic Tachometer Repair Manual12.56 MB.