Use a 12 volt test light or logic probe these external pumps have push on leads for the pump normally. You should have 12 volt on one side and ground on the other side.
http://www.autopart.com/tools/toolsmain/tool/T_3031.htm
http://www.autopart.com/tools/toolsmain/tool/T_3023.htm
These are various type of testers. One does both on the other one hook up to positive and touch the ground.
A Haynes manual should show location of inertia switch. Usually back of a side brace behind an opening.