I am installing a used furnace, approximately 3 years old. I am trying to prime the burner but the pump is not running long enough. The literature I have says to bypass the timer. How do I do this?

By pass the safety control will cause the burner motor to run all the time and allow the pump to prime the system. Usually this is not necessary if the iol line from the tank to burner is tight with no air leaks.

Just jumper the power directly to the burner motor or in some cases you can jump out the cad cell on older safetys.