The red wire w/green stripe is what powers your High Idle and GPC. If that wire was dead, then... yeah. Unpredictable results. "Relay" is in quotes, because to me, it's not a relay but everybody calls it one. Definitions between them vary and there is a lot of confusion about it. But primarily, a relay has a hinge, and a front and a back. The type of device used to carry really high current is more suitably called a contactor. The same thing you might find in your AC compressor outside your house. Any device that uses a solenoid to draw in a bar or pole that has a pair of contacts that move in unison is considered a contactor. For the purposes of most conversations, it's neither here nor there if it is a contactor or a relay, but contactors and relays usually make distinctively different sounds when they actuate, so I like calling them what they are. The solenoid on the fender for your starter motor is also a contactor, where as all the little black plastic boxes in your power distribution block are typically relays. The reason contactors carry heavier loads than relays, is that in a relay, you have a hinge which is typically a bronze or thin flexible metal strip which bends with each actuation. In order for the relay contact to move, the metal strip must be thin enough so that it can bend easily. This thin strip is also responsible for carrying the circuit load, so if you were to make a relay heavy enough to carry the kind of current your glow plugs draw, then the flexible strip would be so thick it wouldn't bend. That's why a contactor is necessary. There is no hinge to flex.
