My 7.3L won't start or even crank over - Page 3 - Diesel Forum - TheDieselStop.com
'99 & up 7.3L Power Stroke Engine and Drivetrain Discussion of the '99 & up 7.3L Power Stroke diesel engine and drivetrain in the 1999-Up Super Duty trucks and Excursions. No gas engine discussion allowed except on transmissions and drivetrain that pertain to all models. Please confine discussion of topics in this forum to those items that are specific to the 7.3L Power Stroke engine.

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post #31 of 54 (permalink) Old 07-02-2017, 09:05 AM
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Thanks RT, this is exactly what I needed! I was literally just looking where I could buy the switch locally but I'll test mine before buying a new one, I'm going to check all fuses and relays one more time too just to be sure -it's just so strange that while replacing the motor I also lost the switch or whatever is killing the power source, but I did have a few no-start mornings before so maybe it is just coincidence.
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post #32 of 54 (permalink) Old 07-02-2017, 12:49 PM
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I am having the same symptoms. In my case it is not the ignition switch (B4 to STA shows continuity when switch in the START position). The problem is that I am not getting power to the wire that plugs into B4 -- should be a constant 12v. Anybody have an idea what should be supplying power to that wire? Fuse? Relay? Having difficulty tracing the wire through the firewall.
--JB
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post #33 of 54 (permalink) Old 07-03-2017, 12:02 PM
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Quote:
Originally Posted by RT View Post
Here's some info - you'll have to get your voltmeter out and work through each pin to see that it is acting correctly with the key in the respective positions:

Attachment 111818

Attachment 111826
RT - thanks for all the help, I tested the ignition switch and it is working properly. I used the other sheet you sent and tested the DTRS connection and didn't get any power on pins 10 or 12 but I'm not sure what that means???

Also, as I was checking fuses and relays again I noticed my fuse panel has a lot of "not used" positions with fuses in them, I pulled them out since they shouldn't be powering anything but those slots did have the metal leads that the fuses would plug into, I think this is so you could add a circuit later but I'm not sure - are the unused positions typically just the plastic "slot" without the metal contacts?

I know the everything from the plug near the passenger fender down to the starter is good, the ignition switch is good, I don't know about the DTRS, and it seems like all fuses and relays are good - just to confirm, not getting power at pins 10 and 12 on the DTRS wire harness doesn't mean the DTRS itself is bad, it confirms I have an electrical issue somewhere that's cutting off power, correct?
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post #34 of 54 (permalink) Old 07-03-2017, 02:18 PM
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Go here: BBB Industries - TSB's & Wiring Diagrams and sign up for free access, you can download the wiring diagrams for your truck, and they include the color codes.

On the other hand, Since your wife drove it last, tell her she broke it and that she has to buy you a new one...

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post #35 of 54 (permalink) Old 07-03-2017, 08:05 PM
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Para_Bellum,
I found my issue and am sharing in the hopes that it'll solve yours as well.
Like you, everything from the starter relay on the fender to the starter is fine. Fuses fine. Tested my ignition switch, that tested fine in all positions. Here's what I did...

Check to see that you have 12v going to your fuse #3 (20A) in the Power Distribution Box. Set your multimeter to DCV, connect one lead to the neg terminal on the battery and probe the fuse with the other lead. Should read ~12v on both posts. If you don't show power, the problem is between the Starter Relay on the fender and the fuse -- most likely one of the fusible links. If you do have power, pull the fuse and probe the terminals that the fuse plugs into to see which one has power. The one that does not have power is the wire going to your ignition switch.

Set your multimeter to Ohms to check continuity. Test continuity between the non-powered terminal and the connector at the ignition switch (B4 in the diagram that RT sent). Mine showed an open line, no continuity.

After much blood, sweat, expletives and gnashing of teeth I traced the issue to a corroded and broken wire inside the Power Distribution Box, which coincidentally was the output wire from fuse #3. A couple of snips, strips, and a $.10 connector later to splice the wire back together and I'm back in business. Once fixed, you should show continuity all the way from the STA pin on the ignition switch to the ignition wire at the Starter Relay, and when you turn the ignition to Start you should see ~12v at the end of that same wire.

Hope this helps.
--JB
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post #36 of 54 (permalink) Old 07-04-2017, 09:35 AM
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Thanks JB, I'll check it out, somewhere in the process I also shorted out my new starter motor but had a lifetime warranty so I replaced it yesterday, spending some time with the family today for Independence Day so I'll try your fix hopefully tomorrow and will report back - thanks again!

Happy Independence Day!
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post #37 of 54 (permalink) Old 07-05-2017, 05:06 PM
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Update: Put a new starter motor in, didn't have time to test the fuses as JB suggested but did try to jump it to check everything from the "fender connection" down - motor just clicked.

When I put a wire between the ignition wire and positive battery connection to jump the starter it is now sparking at the positive battery stud, it wasn't doing that before so I'm not sure what would have changed, does this indicate a short somewhere or bad ground or could it be rooted somewhere in the fuse panel?

If I check the starter ignition wire (smaller wire, not the constant 12v wire) for continuity and confirm there isn't a break in it, what would be causing the new starter motor not to start if it has constant 12 v, 12v ignition when jumped, and a solid ground? I am wondering if by jumping the starter motor off the same battery a few times I could have drained it enough that it's too weak to jump the starter again? On top of this, when I turned the key the wait to start light flashed quickly then the battery light came on but I had no power to any electronics - does anyone have any idea what my actual problem may be or what the source is?

Thanks in advance for any suggestions, I hate chasing electrical issues and mine seem to be getting worse the deeper I look...
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post #38 of 54 (permalink) Old 07-05-2017, 06:24 PM
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Sparking at that stud would indicate a bad connection there. Tighten it up and try again.


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post #39 of 54 (permalink) Old 07-06-2017, 11:55 AM
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Thanks to both JB and RT for the help. I confirmed that the connection was just loose, so I can once again jump the starter motor and drive the truck if needed, though I'm striving to fix the starter issue before leaving the house.


JB - I ran through the procedure you suggested, when facing the dash, fuse #3 which is a 20 amp fuse DOES HAVE power on both terminals, once removed I still have 12v on the left/driver's side terminal and no power on the right/passenger side. I checked for continuity between B4 on the ignition switch and the right terminal of the fuse "plug" and had nothing, open circuit, so I'm wondering if I have the same issue you were having. Before I pull the fuse box out I'm going to do some research to make sure I don't need to disconnect anything (batteries or otherwise) to make sure I don't fry something else. If I don't find a break in that wire (which seems like I'd have to since I don't have continuity there) I may resort to spending $20 on a new DTRS just in case that's the issue and I tested it wrong before.

Can anyone send me the actual fuse diagram for a 2003 F250 with the 7.3? I pulled the official manual from Ford's website but it shows a number of fuses as "not used" INCLUDING the #3 fuse that JB/I tested (see attached photo)- so I'm not sure why but the manual doesn't match my actual fuses, I also have no fuse in the FICM spot (according to the diagram in the manual) but doesn't seem to affect anything...

One more question on the ignition wiring - I attached a photo of something (blue wire) that is spliced into A5 of the ignition switch then runs to what looks like a relay, just hanging off another wire with a zip-tie (follow the red/blue/yellow/brown wires and you'll see the black wire harness that plugs into what I think is a relay), all the other wires for this "relay" are cut or don't go to anything, it's only that blue wire -does anyone know what this is and if these other wires need to be connected? (I know this isn't affecting the starting situation because it's been like this since I bought it but it can't be right the way it is...)
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Last edited by Para_Bellum; 07-06-2017 at 12:03 PM. Reason: clarifying attached photo.
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post #40 of 54 (permalink) Old 07-06-2017, 01:00 PM
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That last photo of yours doesn't look stock. I'm guessing someone put a remote start/alarm in at one time. That relay may be to prevent cranking if the engine is running.

Looks like you have a fun time ahead of you cleaning up.

If I can remember, I'll see if I can get you a wiring diagram tonight.

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post #41 of 54 (permalink) Old 07-07-2017, 09:42 AM
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Bump on the wiring/fuse diagram - anyone have one that looks like my fuse panel? My issue is that the 2003 manual available on Ford's website has a lot of spots marked "not used" that I have fuses in...?
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post #42 of 54 (permalink) Old 07-07-2017, 10:35 AM
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I have found the manual is less than reliable on identifying all fuses. Any slot that has two prongs in it should be considered used by something, so I wouldn't go pulling fuses that were there out all willy-nilly. Ford didn't put extra fuses in unused slots out of the goodness of their heart.

I have an 03 as well, so if it would be helpful, I can take pictures of any area that you need.

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post #43 of 54 (permalink) Old 07-07-2017, 11:12 AM
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Thanks RT, that makes sense, glad to know it's not just something that's not lining up in my truck versus a somewhat unreliable manual.

If you can shoot me a photo of your fuse panel that would be awesome, I'll just make sure mine lines up and fill in any empty spots accordingly. Next step once all the fuses are there is to trace the wires behind it as JB suggested to see if I have a break that's preventing the ignition from actually getting the ignition voltage to the starter motor.
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post #44 of 54 (permalink) Old 07-07-2017, 10:23 PM
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Alright fellas - I'm at a loss. I pulled the central junction box (CJB) and found no breaks or shorts in the wires behind it. Next I traced the starter motor ignition wire back through the firewall and into the CJB, I tested that wire for continuity and confirmed that the wiring from the back of the CJB all the way to the starter motor is good.

I previously tested the ignition switch following the procedure that RT provided (I only tested the four positions for the start circuit) and found no issues.

I thought my issue may be the DTRS/Safety neutral, I swapped the DTRS for a brand-new one but still no luck.

I previously checked all fuses and relays - they all seem to be good.

I have no idea what else I can check, it seems I'm not getting power to/through the CJB to the actual ignition wire for the starter - anyone have any ideas what else I can check or have a diagram of the actual circuitry of the CJB?

Thanks in advance and thanks for all the input from everyone so far, I've been able to narrow this down but still haven't pinpointed the issue.
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post #45 of 54 (permalink) Old 07-08-2017, 09:59 AM
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Quote:
Originally Posted by DieselExhausted View Post
Para_Bellum,
I found my issue and am sharing in the hopes that it'll solve yours as well.
Like you, everything from the starter relay on the fender to the starter is fine. Fuses fine. Tested my ignition switch, that tested fine in all positions. Here's what I did...

Check to see that you have 12v going to your fuse #3 (20A) in the Power Distribution Box. Set your multimeter to DCV, connect one lead to the neg terminal on the battery and probe the fuse with the other lead. Should read ~12v on both posts. If you don't show power, the problem is between the Starter Relay on the fender and the fuse -- most likely one of the fusible links. If you do have power, pull the fuse and probe the terminals that the fuse plugs into to see which one has power. The one that does not have power is the wire going to your ignition switch.

Set your multimeter to Ohms to check continuity. Test continuity between the non-powered terminal and the connector at the ignition switch (B4 in the diagram that RT sent). Mine showed an open line, no continuity.

After much blood, sweat, expletives and gnashing of teeth I traced the issue to a corroded and broken wire inside the Power Distribution Box, which coincidentally was the output wire from fuse #3. A couple of snips, strips, and a $.10 connector later to splice the wire back together and I'm back in business. Once fixed, you should show continuity all the way from the STA pin on the ignition switch to the ignition wire at the Starter Relay, and when you turn the ignition to Start you should see ~12v at the end of that same wire.

Hope this helps.
--JB
JB - now that I've tested everything else and confirmed the issue is somewhere between the key and junction box (but not the ignition switch or a wire that's clearly visible), I wanted to confirm before pulling the junction box again - was your issue a wire INSIDE the box opposed to one that plugs into it? When I re-read your post that's what I am thinking now but wasn't sure if the fuse panel (junction box) actually comes apart to see the wires inside?
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