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Mike S.
Mike S., ASE Certified Technician
Category: Ford
Satisfied Customers: 7568
Experience:  ASE Certified Master Technician
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Won't crank over. Blows fuse #20 on the passenger instrument

Customer Question

Won't crank over. Blows fuse #20 on the passenger instrument panel. Having voltage come out of the small wire coming from ignition the the starter motor relay of the fender. 2000 Ford F-250 5.4L
JA: How many miles are on the car? Has the car been starting normally?
Customer: 150k miles or so. And it won't start without the #20 fuse because the relay doesn't have 12 volts through the ignition
JA: Are you fixing your F250 yourself? What have you tried so far?
Customer: Yes fixing myself. And so far I've volt tested the battery, took a battery load test, tried new fuses, tested voltages on fuses.
JA: Anything else you want the mechanic to know before I connect you?
Customer: I'm getting about 5.5 volts coming out of the small wire on the starter motor relay coil at ALL times with the battery ON. Take the battery cable off and obviously it's 0V. With the ignition at START I t 5.5V and same with the ignition at CRANK
Submitted: 2 months ago.
Category: Ford
Expert:  Mike S. replied 2 months ago.

Hi, I am Mike, welcome. I'm reviewing your question.

Expert:  Mike S. replied 2 months ago.

Try removing the starter relay and if the fuse no longer blows when the key is turned to start, try a new starter relay.

Expert:  Mike S. replied 2 months ago.

Ok, 5.5 volts on which wire?

Customer: replied 2 months ago.
The starter relay isn't the problem. And I'm getting 5.5V on the small wire (ignition switch wire) on the starter relay coil. And it's constant
Expert:  Mike S. replied 2 months ago.

Dark blue/orange if a manual transmission or tan/red automatic?

Customer: replied 2 months ago.
Tan/red as its automatic
Expert:  Mike S. replied 2 months ago.

Remove that #20 fuse and heck the voltage again.

Expert:  Mike S. replied 2 months ago.

check not heck

Customer: replied 2 months ago.
That's without the #20 fuse. I haven't put a #20 fuse in since the problem has been going on. I'll put one in and check the new voltage at the wire to see if there's any difference
Customer: replied 2 months ago.
Voltage is the same. Around 5.5V actual is 5.4V at the wire with #20 fuse in
Expert:  Mike S. replied 2 months ago.

No, instead disconnect the transmission range sensor harness and check for that 5.5 v again.

Expert:  Mike S. replied 2 months ago.

There should be nothing on that circuit until the key is turned to start.

Expert:  Mike S. replied 2 months ago.

Here is that Starting Circuit

Customer: replied 2 months ago.
DTR sensor unplugged and no voltage
Expert:  Mike S. replied 2 months ago.

Ok check the voltage going to that range sensor on the dark blue/orange or white/pink wire.

Expert:  Mike S. replied 2 months ago.

While you are at it while that sensor is unhooked make sure that fuse #20 has no voltage also.

Expert:  Mike S. replied 2 months ago.

If there is nothing at fuse 20 now and also nothing going into that range sensor, the sensor is obviously shorted out and needs to be replaced.

Customer: replied 2 months ago.
DTR sensor has 5.5V at the white/pink wire. Checking #20 now
Expert:  Mike S. replied 2 months ago.

If there is voltage going to that range sensor check again at the clutch switch bypass jumper behind left side of dash.

Customer: replied 2 months ago.
There is 5.5V at the #20 fuse. And how do I check clutch switch bypass?
Expert:  Mike S. replied 2 months ago.

First of all remove the fuse and see which side of that fuse socket has that 5.5 volts.

Expert:  Mike S. replied 2 months ago.

the clutch jumper should be where a clutch position sensor would be.

Expert:  Mike S. replied 2 months ago.

or near it.

Expert:  Mike S. replied 2 months ago.

as far as the fuse socket goes, the side from the battery would have the 12 volts when the key is on start, the other side goes down to the range sensor so see if that 5.5 v is on the same side that is hot with 12v when key is on start or not.

Customer: replied 2 months ago.
Left side is where 5.5V is coming from on the #20
Expert:  Mike S. replied 2 months ago.

That tells me nothing. I don't know right from left.

Expert:  Mike S. replied 2 months ago.

Which side has 12v when key on start?

Customer: replied 2 months ago.
Neither. Key on or off the one side has 5.5v and the other has 0V without the fuse
Expert:  Mike S. replied 2 months ago.

make sure you didn't pop the other #20 fuse under the hood in the battery junction box.

Customer: replied 2 months ago.
20 under hood is good. Has full 12V to both sides
Expert:  Mike S. replied 2 months ago.

It is obviously not on that side of that fuse anyhow, since you still had that 5.5v with that fuse out.

So check that fuse under the hood ,, get that working then check for a short a the clutch jumper.

Expert:  Mike S. replied 2 months ago.

Then you have more than 1 problem. Maybe a faulty ignition switch as well as a short of 5.5 to that start circuit.

Customer: replied 2 months ago.
Let me check the clutch jumper. Got to find it first. Have no idea where to look.
Expert:  Mike S. replied 2 months ago.

Find hat clutch jumper switch and disconnect it and check both wires for voltage there.

Expert:  Mike S. replied 2 months ago.

Look under the dash where a clutch pedal would normally be.

Expert:  Mike S. replied 2 months ago.

find it?

Customer: replied 2 months ago.
Just found it and tested. There are 2 white/pink wires, both have 5.5V, dark blue/orange has 0V
Expert:  Mike S. replied 2 months ago.

Well, them white/pinks go in and out, just ignore the dark blue/orange, that must have been if there was a manual trans.

Expert:  Mike S. replied 2 months ago.

Disconnect them white pink wires and now do both still have 5.5 v or just the one

Expert:  Mike S. replied 2 months ago.

Depending on which one and I will assume it's only 1 either that wire goes back to the fuse or it goes to the range sensor, so it would have a short circuit. You will just have to trace the wire and find out where the short is. or just cut both ends and run a new wire.

Customer: replied 2 months ago.
They aren't connected to anything. The cable is attactched to a "stopper" with little prongs on the inside I assume for stopping the connection. I took that stopper off and put my voltmeter in the prongs and tested all 3 wires. The 2 white/pink ones showed 5.5V
Customer: replied 2 months ago.
trace the wire back to where? To the steering column?
Expert:  Mike S. replied 2 months ago.

Wherever it goes, but first you will have to somehow separate those 2 white/pink wires so you can test each individually.

Expert:  Mike S. replied 2 months ago.

It's not for stopping the connection, it is a jumper to connect the 2.

Customer: replied 2 months ago.
Is there any way you can get me a full wiring schematic on the ignition system? The one you gave me was very vague. And I just assumed because the only metal inside the stopper is the prongs that go into the female end of the connector and they don't seem to be connected. Is there anything I can do to narrow down where the wires run?
Expert:  Mike S. replied 2 months ago.

The one comes from that #20 fuse and the other goes to the range sensor.

Expert:  Mike S. replied 2 months ago.

Here is the entire power distribution showing the ignition switch on page fig2.

Expert:  Mike S. replied 2 months ago.

No wait, them 2 white/pink wires are for either/or auto or manual.

Expert:  Mike S. replied 2 months ago.

So they should both be hot when key is on start, but not with key off and surely not 5.5v.

Expert:  Mike S. replied 2 months ago.

Then the problem is between there and back to that fuse and could be inside that central junction box itself and a rusted/shorted out box.

Customer: replied 2 months ago.
I need to take the central junction box out and check in there for a shorted wire? Is the central junction box the instrument fuse panel?
Expert:  Mike S. replied 2 months ago.

See if you can disconnect the harness from that central junction block and then run those tests again and also on pin 4 of that harness where that white/pink wire is.

Expert:  Mike S. replied 2 months ago.

It is behind lower left side of dash.

Expert:  Mike S. replied 2 months ago.

It is where that fuse #20 is. Not the one under the hood.

Customer: replied 2 months ago.
Okay, how do you disconnect the harness?
Expert:  Mike S. replied 2 months ago.

Look for clips on both ends.

Expert:  Mike S. replied 2 months ago.

I don't have any further info on how to unhook it.

Customer: replied 2 months ago.
I found out the two plugs on the back of the central junction box (instrument fuse panel) have 1-10mm bolt in each holding them in. I don't have any tools on me at the moment besides a couple screwdrivers and voltmeter and wrenches. I will get back with you shortly after I get these out and test those wires and let you know what happens. Thanks
Expert:  Mike S. replied 2 months ago.

ok

Expert:  Mike S. replied 2 months ago.

Any news?

Customer: replied 2 months ago.
No sir, can't get to it until either later tonight or tomorrow. I'll let you know. Thanks!
Expert:  Mike S. replied 2 months ago.

Roger that...

Expert:  Mike S. replied 2 months ago.

Find the problem yet?