94 5.7 to 98 7.4 questions about wiring

[Nobodys94]

Truck is a 94 with this 5.7, I have everything from a 98 3500 7.4 vortec except dash harness. I have the AC system and the wiring from the firewall to headlights. Fuse box and computer. Is the wiring harness plug and play? Can I repine it to work with my 94 firewall. Plug so I don't Have too swap dash harness. Will the vortec computer run my built 4l60e trans
:
Other option is megasquirt and megasquirg wiring.

I wanna stay mpfi on this.

 

[Truckingeek]

Recently I swapped in a 98 4.3 into my 94 C1500. I cannot answer all your questions but I do have a couple of answers. The dash harness will need to be custom built. The old 94 dash relied on analog devices to report the temps, speed etc. The 98 sends most of this info to the PCM then digitally to the dash. Speedo will work fine, fuel gauge will work but more than likely will have the "Hummingbird effect" meaning it bounces around very fast. Temp gauges and oil psi will work with a little wiring. Cruise control will also require a little custom wire work.

The fire wall of my truck still looks like somebody threw a 100 pounds of scrape wire in the engine bay and closed the hood, but it is a work in progress.

If I was to do it again I would make the wiring harness for the new engine a "stand alone" deal by removing any wires not needed for just the engine. Then create smaller harness's as needed for the cruise, ac, etc.

I can provide you with some schematics to help you figure out what runs where if you need them.

 

[Truckingeek]

1998 7.4L Vin "J" Engine Performance Schematics

Hope these help you.

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