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Discussion Starter · #1 ·
Got a 96 that I just replaced the relay on. KOEO, I get 12+v to all three posts except the glow plug side, also not continuity between the large posts
Motor vehicle Automotive tire Vehicle Automotive exterior Car

. What is the operation of the OBS relay? I know the SD is a ground from the PCM and +v key in the ignition.
 

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It's the same as the super duty, the PCM provides the ground. So if you are not getting the ground when the key is first turned on there may be a broken wire, a PCM problem.

You will see voltage on both sides of the coil, the small terminals because all that is there is a coil of wire from the key on power source going through the coil of wire to the other terminal.
 

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Discussion Starter · #3 ·
Figured they would have used another color wire besides red for a ground voltage wire. What is the black plug for they run through? I get voltage when I check between both small posts and the negative battery post.

Now I just discovered in installed my spare starter relay. Glow plug relays are brown. I had the glow plug relay in tge door pocket, and the starter replay in the console 🤦‍♂️
 

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Figured they would have used another color wire besides red for a ground voltage wire. What is the black plug for they run through? I get voltage when I check between both small posts and the negative battery post.

Now I just discovered in installed my spare starter relay. Glow plug relays are brown. I had the glow plug relay in tge door pocket, and the starter replay in the console 🤦‍♂️
One of the heavy posts has twelve volts from the battery to turn on the glow plugs if the soleniod contacts are activated. The other heavy post does NOT have 12v because the solenoid is not being activated. One of the little posts has a 12v supply to feed the magnet in the solenoid switch. The other has 12v that comes through the magnet coil which is, apparently, not getting the necessary ground from the engine computer to activate the coil and turn on the glow plugs. If you want to cheat you could run that to a pushbutton or toggle switch to turn on the glow plugs manually. This will be the wire that does NOT have 12v if removed from the solenoid.
 

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That may be a early 96, in 94 and 95 they had a plug in connector on the glow plug relay and the fix for it was to have a plug that brought out the wires onto eye connectors to connect onto the relay.

If you had a starter relay connected you would quite possibly have power to the glow plugs as long as the key was on since they are a case grounded relay and as long as there is power it will be on.
 

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That may be a early 96, in 94 and 95 they had a plug in connector on the glow plug relay and the fix for it was to have a plug that brought out the wires onto eye connectors to connect onto the relay.

If you had a starter relay connected you would quite possibly have power to the glow plugs as long as the key was on since they are a case grounded relay and as long as there is power it will be on.
That may be a early 96, in 94 and 95 they had a plug in connector on the glow plug relay and the fix for it was to have a plug that brought out the wires onto eye connectors to connect onto the relay.

If you had a starter relay connected you would quite possibly have power to the glow plugs as long as the key was on since they are a case grounded relay and as long as there is power it will be on.
Yes, a starter relay has a "hold-in" coil.
 

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The glowplug relay (GPR) must be case-isolated (not connected to ground) as mentioned, or the GPR will always be "ON". To check the GPR, measure the voltage drop across the GPR's large terminals. While the GPR is active (up to 1.5 to 2 minutes after the key is turned to Wait-to-Start) put your meter leads on the large terminals (one lead on one large terminal and the other lead on the other large terminal). This measures how much voltage is being "lost" across the relay. A reading of 0.3V or more indicates a bad relay. Also, check the relay’s control wires (smaller wires) disconnected from the relay for battery voltage at the Red/Light Green striped wire and ground at the Purple/Orange striped wire (check both when the key is turned to Wait-to-Start). Cheers!
 
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