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1987 - 1996 F150 & Larger F-Series Trucks 1987 - 1996 Ford F-150, F-250, F-350 and larger pickups - including the 1997 heavy-duty F250/F350+ trucks

Ignition relay.

 
  #1  
Old 05-17-2016, 06:38 PM
roots4thought
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Ignition relay.

So I'm sorta stumped here. I have an 87 f150 i6 300 mt 2wd.
I have power at the ignition relay (brown) at the 12v constant (yellow) wire and when I turn the key to run I hear the relay click. I tested the 12v from the keyed ignition switch by pulling off the relay and checking for voltage with my volt meter. Checked ground wire by putting the red side of my volt meter to the + post on batt and the black side of meter to the ground wire. Everything checks out fine. When the relay is installed, and the key is on, I do not get voltage through the relay to the "out" side of the relay. I have tried 3 different relays including the old/origional one and two brand new ones from two different manufactures. When I jump the 12v to the "out" on the plug with the relay removed I can get the truck to fire right up and run. What is going on here?
 
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Old 05-17-2016, 07:15 PM
bigredtruck
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Is the 12V from the keyed ignition switch the power to the relay that is supposed to pass through it, or is that the 12V to energize the relay coil to pull in and close the circuit?
 
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Old 05-17-2016, 07:27 PM
roots4thought
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The 12v is to pull the coil
 
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Old 05-17-2016, 07:35 PM
bigredtruck
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So, 12V in, 12V keyed, relay clicks, but no 12V out tested on multiple relays.......

All I can guess is the relays have normally open contacts and normally closed contacts. See if you are getting 12V out of any of the leads when the key is off. That would mean the output lead is wired to a normally closed contact with no power applied and when you turn the key, it is opening the circuit.

Just a guess.
 
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Old 05-17-2016, 08:41 PM
roots4thought
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There are 4 wires

1.) yellow wire is always hot/12v
2.) black ground
3.) red key in 12v closed circuit.
4.) brown normally open supply to computer, fuel pump relay, distributor etc etc

When I jump from yellow to brown I get the truck to run.
Red and black are purely to pull the coil and complete the yellow to brown connection.
 
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Old 05-18-2016, 07:01 AM
roots4thought
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Thank you bigredtruck for your responses. I hope that somebody else may have a suggestion as to what I can look at or a test I can perform.

The only thing I can think of is that the ground is maybe not good? It is grounded according to my meter but maybe something changes when a load is applied?
 
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Old 05-18-2016, 07:34 PM
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I opened up the relay and I am not seeing the coil engage. I hear it click but do not see it latch. Guess I'll try the ignition switch
 
  #8  
Old 05-19-2016, 07:41 AM
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Sounds like a bad relay socket or the wires to the socket.
Very common with this era truck.
Most just update the socket and relay to the newer type.By the way the relay you are calling the Ignition relay is called the EEC Power relay.

Here is a diagram for making the update:


/
 
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Old 05-19-2016, 01:06 PM
roots4thought
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Originally Posted by subford View Post
Sounds like a bad relay socket or the wires to the socket.
Very common with this era truck.
Most just update the socket and relay to the newer type.By the way the relay you are calling the Ignition relay is called the EEC Power relay.

Here is a diagram for making the update:


/
Subford you're the man. I'll replace the socket today
 
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Old 05-19-2016, 01:59 PM
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Ok, took the socket apart and wired directly to the relay spades. Still won't engage the coil. I checked that all the terminals are getting power where they need it and ground as well. The only one not getting juice is the supply to the computer. I wired in a manual eec relay (switch) for now. Kinda a pain to have to flip but it works and the truck runs like a champ!
 
 
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