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"Wait to Start" Relay is really easy to install, and will help pro-long the glow plug by preventing you from starting while they are heating up.
You will need a 12 volt relay with Normally Closed (N.C.) set of contacts rated for 1 amp or better. Radio Shack's 20-30 amp Automotive relay will do fine. And a few feet of 18 ga. wire
A Diode 1N1004 (added protection to be added to the relay) 1 Amp diode @ 400 PIV (you can get this too from Radio Shack) Connect the white band side of the diode to # 85, connect the other side to # 86. Either solder it to the relay or crimp it in with your wiring. This is to prevent high voltage spikes from the relay when relay is de-energized getting into the "Glow Plug Controller".
Locate orange wire coming from the "WAIT" light just under the right side of the dash.
Locate Starter Relay that is behind the fuse panel cover on the lower right side.
Take one side of the coil ( + side if marked or # 85) and connect it to the orange wire that goes to the "Wait" light and take the other side of the coil (# 86) to ground. Remove the light blue wire from the Starter Relay ( # 86) and connect it to the new relay contacts N.C (# 87a). Install a jumper from the "Starter Relay" coil ( # 86) & the new relay common (# 30). - - - You are now complete.
If the "WAIT" light is on you should not be able to start the engine until the light goes out. If so you are complete. If not make sure you are using the Normally Closed set of contacts on your new relay.
I promised a step by step guide to self install this feature on Hummers. It will not allow a Hummer to crank until the glow plugs are hot. So get in and turn the key it will start when it's ready. Jeffery J. from Dallas is coming down on tuesday with his 1996 turbo wagon. I will get the actual Hummer wire colors and post them next week. This is the method of installing the relay. First you will need one 30amp 5-pin realy(Bosch,Hella,etc.). With relay pins towards you notice the pins are marked. EX: 85,86,30,87a,87. Now locate the crank wire in steering column.(this wire will only be hot in the crank mode"key all the way forward"). Cut this wire in half, then connect each side to pins 30 and 87A. It does not matter which side goes to which pin. Now ground pin 85 to chassis ground. The last connection is the hardest. Find the +12volt side of the wait to start light. This wire switches to +12V when the light comes on, and then loses power when light goes off. Tap into this wire and connect to pin 86. You may need a diode to isolate the "Wait Light" if it rests at ground. If so add a 1 amp diode(band towards pin 86). I'll post the wire colors and locations next week. This will save your glow plugs from eager starters.
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