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1994 7.3 going into 1990 F-350- wiring harness questions

Discussion in '6.9L IH & 7.3L IDI Diesels' started by Jimmy Wells, Aug 4, 2020.

  1. Jimmy Wells

    Jimmy Wells Registered User

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    1. Should I keep the old alternator (external voltage regulator) and bring that wiring harness over to new engine so I can just plug in and go or do I want to use the '94 (internal regulator) alternator?

    2. If I keep the 94 alternator what's involved in joining the old and new harnesses?



    I figured why start from scratch and tracing every single wire when there are probably 50 guys on here that have done this exact same project.

    Thanks!!

    JW
     
  2. franklin2

    franklin2 Full Access Member

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    Are you going to keep the serpentine belt? The newer alternator really needs that belt to operate properly and to get the most out of it. If you really don't need it, I would use the old alternator with the v-belt setup.
     
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  3. Jimmy Wells

    Jimmy Wells Registered User

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    I plan on keeping the serpentine belt.....
     
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  4. aggiediesel01

    aggiediesel01 Full Access Member

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    Do you have the alternator harness from the '94? If so, it's plug and play, completely remove the '91 alternator harness and regulator and plug in the '94 one. The connectors are different colors but the interlock tab matches with its receptacle on the other half. That harness will likely have a slightly different set of connectors for the A/C compressor though. When ford went to R134 in '94 they added a high side pressure switch on the outlet of the compressor so you'll have to bypass that or use it. Since you're using the serpentine belt system you'll probably want to convert the A/C as well which involves getting the new style common hose assembly from the accumulator to the compressor to the inlet to the condenser and the newer style condenser which is more efficient. If you don't have/want A/C rockauto sells the Idler Pulley and bracket that goes in place of the compressor.

    If you need to use your '91 harness for the 3G alternator, you have to remove the regulator and jump two of the pins in that connector I can't remember exactly which two but look for Homlessduck's recent thread about his '92 truck. It had the 3G upgrade done and someone posted what you need to do. Then you have to graft the 3G alternator plug in place of the old plug at the alt. You also really need to run a heavier gauge wire for the main charge wire from the alt since the new alt is rated for double the output of the old one. That really makes the '94 harness swap a better option if you have or can get it.
     
    Last edited: Aug 8, 2020
  5. renjaminfrankln

    renjaminfrankln Full Access Member

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    Along the same lines, does anyone know what the 4 pin relay/switch thing on the IP wiring harness does?
     
  6. franklin2

    franklin2 Full Access Member

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    Where is this thing mounted and what are the wire colors?
     
  7. aggiediesel01

    aggiediesel01 Full Access Member

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    If you are talking about the little 1" square brick hanging of the side of the harness near where the IP/Fuel Tower wiring joins the main harness, that's the WIF module. It monitors the water in fuel sensor and turns on the associated light on your dash when it gets wet.
     
  8. renjaminfrankln

    renjaminfrankln Full Access Member

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    thanks. I figured it out and cut all that stuff out. I have cold advance and the glow plugs wired to toggles on the dash. I may add a water in fuel sensor back in later
     
  9. franklin2

    franklin2 Full Access Member

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    I wired my cold advance to a toggle since when I bought the truck the temp sensor for that was bad. After trying it out for awhile, I found no real advantage to it, and I found myself forgetting to turn it off. So I took it back out. You may find you end up in the same situation.
     

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