1996 F150 2WD, 5.0
I am seeking some assistance on a friends truck trying to solve a problem. Basics, truck was running fine and he backed into a utility pole at 10 mph and the truck died. He tried restarting it and the PCM fuse blew. He worked on it and replaced the PCM and still blows the 30A fuse. I put a meter on the power distribution power wire coming into the box and it shorts to gnd. I removed the power wire and meter it and it was good no gnd'ing out. As I go through each of the fuse and place one probe to gnd and touch each side of the the fuses they all go to ground, as I was moving the power box around and testing the fuses it stopped shorting excpet the 30A PCM fuse. A little more moving and twisting the box they all went back to gnd.

Today worked more on this. Disconnected the attached firewall connector and the short to gnd on the power distribution box ceased. The connector doesn't short when inserted only when the 10mm screw is tightened. So with the connector tightened removed the instrument panel and disconnected all connectors and still shorting to gnd. Removed the interior fuses one at a time and no effect on the shorting. Disconnected headlamps, fuel switch as well. Then went to right side behind glove box and disconnected the control module there and 4 other connectors, still shorting to gnd, checked fuel inertia switch.

I have noted pins 67-70 of the male side of the connector (from fuse box) goes to gnd, the female side only 70 goes to gnd. Does anyone have a schematic for the pinouts of the attached connector or have an idea of what to check next?

 

Not sure what you mean by" shorting to gnd".
If you are using an ohm meter just about all wires will have a path to ground. But the resistance will very depending on the device it is going through.
Replacing the computer when fuse #9 blows was a bad idea as this fuse powers the red 361 wire and it goes every place beside going to the computer. Why did you not just unplug the computer and see if the fuse still blows?
If it did then you could replace the fuse with a circuit breaker as you unhook circuits for testing.

Here is a pin-out of C202F you wanted but circuit 361 dose not go through C202F.

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Bill, thanks for your response, another person worked on his prior to me and replaced the PCM. By short to gnd I mean if I put a probe on the power input (yellow wire) to the power distribution box and touch ground, its a dead short. If I unplug the PCM connector stll show gnd, if I unplug the C202 the short to gnd stops. My thought was something on that circuit is causing my problem. is that a correct assumption?

If I connect up the battery and turn key ON the 30A fuse blows immediately.

 

Pin #70 circuit #38 does not go to ground:


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Sorry, I edited that post once re-read it

 

The wires going through C202 is not the problem.

As far as the yellow wire goes here is a lay out of that power distribution box.
It is for a 1994 but I think it would be close to what you have. Note in 1996 the fuses have numbers and not letters.

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Power from that 30 amp fuse does not go through C202.
When you unplug C202 and turn on the key the PCM Power relay does not pull in is why the fuse does not blow at that time.

Your problem is in the 361 circuit.

 

Where can I get information on the 361 ckt for this 96 5.0?

 

It is the red wire coming out of the PCM Power relay in the diagram below:


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Thanks Bill I will get back on this later today.

 

Spent a few hours on the truck today.

I checked each of the 361 circuit locations Red wire, all went to
gnd. I pulled the PCM connector and checked the engine side of
the Red wire, connector pins 71 and 97 and they show gnd.

I looked through the wiring and do not see any bad or cracked or frayed sections from what I looked at.

I disconnected the connector harness to the O2's, the side bringing the power to the connector shows gnd on the pins, the side that goes
out to the O2's doesn not show gnd on its pins.

I noticed if I remove the PCM connector, no longer does the IAC, MAF Starter Solenoid or EGR show gnd on the red wire until I plug in the
PCM connector to the PCM in the truck, or the original one that
the other gentleman replaced. Not sure if that's of any significance.

Any ideas?

The only way I can stop the short to gnd is to remove the 76 pin
connector from its female mate on the firewall.

I have tried disconnecting all connectors within the dash while metering
the input power (Y Wire) on the power box and a chassis gnd node.I would
have thought one of those connectors once separated would have
stop the gnd connection. As I stated earlier I removed each of the
interior fuse box fuses while metering as well. Nothing changed the state
of the Yellow power box lead shorting to gnd.

This all happened after a 5-8mph backup into a tree. I checked all the wiring
in the rear of the truck for bare or pinched wires. I checked the fuel inertia
connector on the passenger side, separated the connector and didn't effect
the Power Box yellow input wire shorting to gnd.

Being I have looked st so much it has to be something very simple I am
overlooking, making it more complicated than what it is... sigh....

 

As stated earlier the red 361 wire does not go inside the cab of the truck and unplugging the fire wall connector just keeps the power relay from closing. With the power relay not closing the red 361 wire does not have any power on it. It also does not go to the starter relay on the fender.

 

Morning, I understand that I am just trying different tests. The starter solenoid doesn't connect to the 361 circuit but I thought it was a relevant test and was surprised to see gnd and power shorting together there with the battery unconnected.

When I get lost like this I just start looking everywhere for evidence of where the problem may be.

Knowing everything is shorting to gnd and not seeing any evidence of bare or exposed wires and all this happened because of a slow bump to the rear bumper I am testing and posting whatever I find

 

All of these wires can not be shorted to ground. Tell me again how you are determining they are shorted to ground.
I know you are saying the fuse that powers the red 361 blows when you turn on the key.

If the 361 wiring is shorted to ground I would think it would be the O2 sensors or the transmission wiring on the passenger side. Those two places is about the only place it goes under the truck.
As I noted above just about every wire goes through a coil to ground and that would mean very low resistance to the ground return wire.
You would have to unplug every plug that the 361 wire goes to and then check for the wire being grounded.

By the way what are you using as a ground reference?

 

Morning Bill, I took off today and going up to the truck. I will check the trans wiring and also record the readings I am getting, perhaps I am misinterpreting the gnd state. So here is my setup, I have all connections plugged in, battery is disconnected and I am placing the meter on continuity mode.

I also want to thank you for being so patient with me while trying to resolve this.

I will update later this afternoon.

Tauni