I have bought a low mile 98 model 5.9 Magnum with all of the engine wiring and ECU, and will be putting it in my beater truck. 88 D100 has a TBI 318 in it now. I want to use the MPFI that is with the 5.9. My question is, does anyone have a step by step process for converting the existing engine wiring with the 5.9 to work in older vehicles? I know I could send the harness to several reputable place and let them do it, but I don't want to have more money in the harness than what I paid for the truck! Yes, I'll admit that I'm being a cheapskate....lol. Any help or ideas appreciated!

A 95 and earlier harness and PCM would be easier to make work than the later JTEC controller.

That's kind of what I've gathered from what info that I have been able to find. I don't suppose it matters what a 95 or earlier harness comes out of, as long as it's a Magnum vehicle? Truck, van or Jeep should work. If it matters, the truck that my motor is coming out of is a 3500 5 spd truck, and I will be using an automatic.

Any pre OBD-II 95-down V-8 magnum harness should fit the bill. The manual trans PCM will help considerably in the conversion since there will no transmission controls needed.

I just did this to my 88. Great conversion.
http://ramchargercentral.com/mopar-trucks/1988-w-100/50/

Using anything 96 and later except the engine will greatly complicate things. 92 and 93 trucks are the preferred donor but tough to find.

Only thing that got me was engine mounts. I swear they moved the holes in the crossmemnber from 88 to 92 b/c it was a PIA to get the engine seated. It still sits 1 inch farther back than my stock 92

I'm planning on using the 318 motor mounts back on the 360. I know I will have to shim the drivers side, and have done it before. It's funny how even with the cavernous engine compartment of these trucks, that it's such a pain to get the motor set down in place! I had an 84 D350 with a 360, and had it out a few times. I finally figured out that I needed to leave the insulators a little loose on the mounts to make things easier. I'm hoping to find a simple solution to the wiring.....but I might get to hope for a while! LOL. Thanks for the reply and the link.

When I converted my '87 D250LE to 5.2Magnum/A518 I had a complete '92 D250 Donor. I went ahead and swapped the whole harness from the headlights to the taillights. The factory bulkhead connector hole fit just fine with the new harness but there was a whole extra bundle of wires I had to drill a hole for right next to it. The new computer bracket bolted right in where the TBI computer was. The instrument cluster was a direct swap using the late harness.