Originally Posted by Ponyboychris

GPR = Glow Plug Relay. It energizes your glowplugs at start up. It can be up to two minutes after you first start the engine. (The GPR is working long after "wait to start" light on the dash goes out - a common misconception. FYI). If you are seeing 11 -12v at intial start up but the volts jump to 13.5 - 14v after the GPR stops working, then your alternator is working properly. If you look on top of the engine, behind the plastic Power Stroke vanity cover (if you still have it) there are two relays to the passenger side of the engine between the valve covers. The relay to the rear is the GPR.