1988 F150 4.9L - complete electrical system shuts down when key is turned on.

Asked by Oct 04, 2016 at 09:21 AM about the 1988 Ford F-150 S Standard Cab LB

Question type: Maintenance & Repair

This truck has not been run for 5 years. Battery was replaced. Initially, when the ignition switch was turned on, the electrical system would turn on with all components (radio, lights, etc.) working. When I moved the ignition switch to the start position, the solenoid would click once, and the entire electrical system shut down. After a short period of time, a relay next to the EEC connector terminal near the air box, would click, and the entire electrical system would reboot. I replaced the starter, and solenoid, to no avail. I put a voltage tester between the negative terminal and the engine block and noticed I was getting a 12 volt reading. Through a process of elimination with a wiring diagram, I was able to determine the source of this voltage reading was through the ignition wiring harness connected to the positive side of the starter relay (solenoid). When I disconnected this lead, the block to negative reading went to 0v. A secondary problem is now occurring. The reset time is growing longer, and the electrical system shuts down when turning the ignition to the on position, as opposed to the start position as earlier stated. This is with that ignition wire either connected or disconnected. Since the last time the ignitions switch was turned on, the electrical system has not rebooted. All connections are tight and clean, and the batter reads 13v.
Thanks for any input. I know through my service manual there is a barrage of testing that can be done, but this truck is not at my house. Tools and research materials are not easily accessed.

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