98.5 24valve to 96 12valve....anyone done it?

[CMartin]

I am in the process of swapping a 12v into my friends 98. 5 and obviously the wiring is very different. Has anyone done this swap (or similar) and can you tell me what you did for wiring? I know I can splice the harness's together from 24v to 12v, but that seems very time consuming... . is it the ONLY way? Thanks for any help. CHAD



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[CMartin]

Ok, so I wired up the fuel shut off solenoid and jumped the starter... . the 12v seems to run real good! The more I look at this wiring mess, the worse it looks. I find it odd that no one has responded on this topic yet?? I guess there are just not that many people going from 24v to 12v huh?

 

[COWBOYDUALLY]

I dont have any suggestions for you but i am currently repowering a 1 ton chevy with a 97 12er. i own a 24v but curious as to why the conversion your doing?... . jeremy

 

[CMartin]

Well, the truck belongs to "Cummnzpowr" in this forum. He had the infamous "53" block with one hell of a crack... . and he decided to put the 12v in because he likes the 12v engine better... . as do I. Technically, the engine will be very easy to rewire since it needs very little to run, but he wants his stock gauges to work of course so I am really having a tough time figuring out which way to go with the rewire of the PCM. The 24v guages and sensors are wired through the ECM on the side of the block and the 12v obviously does not have an ECM or that portion of the wire harness... . so I have a lot of cutting and splicing to do

 

[Lightman]

Your easiest option would be an ecm and harness from a 98 12valve. it will plug right in

 

[CMartin]

Your easiest option would be an ecm and harness from a 98 12valve. it will plug right in

Well, we ended up getting a 98 12 valve harness... $350 later and still nothing works right. The harness does plug into the relay box on the drivers fenderwell, butthat leaves the 3 plugs up on the left firewall wide open and nothing to plug into. I have ultimately decided there HAS to be some cutting and splicing, but I just don't know exactly WHAT to cut and splice. With the limited amount of replies I have received it is obvious this swap is not very common whatsoever... . but I appreciate the help so far. I guess will have to figure it out and post up a an article for future reference.

 

[dcoffman]

Martin, have you tried to get a wiring diagram of both and go from there?

 

[CMartin]

Martin, have you tried to get a wiring diagram of both and go from there?

Yeah I actually have all the wiring diagrams and at this point I have most things up and running, but I am working on getting the fuel sender to read, the speedo to work, check engine light to go out and minor small details. The biggest problem is that in 98 12valve there is one under hood harness... . 98. 5 24v there are 2 harness' and they work together. I have to find the wires from the second harness that ONLY the 24v uses and tie them into the single harness of the 12v style. Here is a pic that might help explain me better.



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