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2006 f150 has short indicated in circuit with f12

 
Old 04-17-2019, 02:30 PM
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Default 2006 f150 has short indicated in circuit with f12

Com relay coil the test light goes out when I pull fuse f12 indicating the short is in that circuit for pcm relay coil. Truck won't crank with fuse out. Put fuse back in and truck indicates there's a short by test light lighting up but truck starts up a runs normal except the dash indicators on left side are lit up and no speedometer or Rach and temp guage doesn't work. Already tried switching the relay
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Old 04-18-2019, 02:37 AM
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Default A heavy load or relay coil may look like a short

But it doesn't blow fuses . So no its not shorted then . Load test lights could be used in parallel to feed this circuit each bulb would get dimmer as they share the load .Sounds to me you could have bad dash cluster or check grounds in left and right kick panels .You need to ammeter this circuit to see what it draws over time not just what it draws when first energized .
This is not an easy one to find .
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Old 04-18-2019, 11:32 AM
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Thanks already replaced the cluster, battery, alternator and ignition switch and have checked all grounds and every bit of wiring and pugs that I can see even pulled the fuse box checking for corrosion. I am not seeing anything. I appreciate your input.
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Old 04-18-2019, 01:12 PM
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Default Are you saying it is running your battery down

I have searched for f12 on my diagrams but haven't spotted it on my 05 drawings . I have to look in my book for the fuse assignment layout . Did any of your repairs fix any symptoms at all . I mentioned grounds and corrosion because it cause so many weird symptoms. Of course so is rat/squirrel chewing wires .which is common . You grounds in left and right kick panels should be cleaned .
Your tach comes from crank sensor after pcm ,Temp comes from engine under intake I believe .CHT cyl head temp . Speed should come from sensor on transmission to pcm to cluster .
Wiring to send to pcm on these are in the engine bay where the pcm lives . I'm thinking of a common routing of wires going to pcm on passenger side . I can't think crank sensor signal loss would allow the truck to run tracing the path of the CHT sensor under intake ? tracing crank sensor wires . I am not clear on the path whether some may go direct to dash cluster or can bus signal or damage to wires under dash to cluster . I am going to learn and ponder this point .
There has been damage under intake and near pcm on ac lines and vibration rubs on wires etc . A diagnostic tool would look for these raw signals, possibly VSS ??

This is what I've found on f12 I just can't find it on diagram .
There s a lot smarter guys on here ,hoping they can clear the air .
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Old 04-18-2019, 02:05 PM
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No the battery keeps a full charge the truck runs and drives perfectly it's just all indicators on left side of cluster are lit up and Rach, speedometer and temp guage don't work and the diagnostic port won't link even though the fuse for it and cigarette lighter works. I am currently cleaning all grounds again and going to check for any chewed or wore wires. Thank you very much for your input.
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