JacobCanale

Hey y’all,

Currently looking at the option of LS swapping my Jeep MJ as a fun project, and to gain some more hps. I am new to the engine swap thing, so there are a few things that I have questions about if someone out there is kind enough to help me out 🙏. Fair warning, some of these are gonna be dumb questions.

I feel fairly comfortable as far as actually getting the engine in the Jeep, as Novak has made quality motor mounts and has a radiator fan setup that would work. What really scares me and what I can’t seem to wrap my head around is the engine wiring harness. I’m not at all familiar with how engine harnesses work, but would like to learn.

What exactly would need to be removed from my 1989 Renix jeep?
Are engine wiring harnesses separate from the wiring harness for the interior components?
How would the Jeep ignition communicate with the starter for the LS?
Is there anyone out there who can modify a stock LS harness to be plug and play for a Renix era jeep?
Would the lack of an OBD2 port be problematic?

Any help is appreciated. Sorry if some of these are super dumb questions, I just can’t seem to find a place that explains all of this in a way I can understand haha.

4.3L XJ

The real trick is using the LS harness and blending it with the Jeep wiring. What I did and is the easiest is using a stand alone harness from someone like Painless Performance Wiring. If not them, a local hot rod/custom car shop can so it for you

JacobCanale

How do standalone harnesses work? From what I’ve read it is just the barebones to run the engine, which is fine. What would that mean for removal of the Jeep wiring harness? Also, how does the Jeep ignition system hook up to the standalone harness?

TrailerTrash

The only part of the Jeeps ignition that would be kept would be the key switch. The ecu, fuel injectors, distributor, ect would absolutely not work with the LS. The standalone harness runs the LS ignition and everything else on the engine independent of the rest of the vehicles wiring. But it still has to be wired into the vehicle in order to run.

If you buy a premade harness that will cut out alot of work on your end.

Have you thought about transmission and transfer case options?

4.3L XJ

Also, bear in mind that you have to make the transmission work. If you have a standard tranny, then the ECM needs a speed sensor to work so it will know if the vehicle is moving. The stand alone kits have a relay for the fuel pump and all you do is hook up a brake light wire and wire from the ignition and AC. Not sure how I would blend an AW4 with the Chevy ECM. If you want an auto tranny, you will need to have the Chevy trans to go with it

JacobCanale

Ah ok that clears things up a whole lot! Thanks for that info. I’m most likely going to get a 4l60e as it seems to fit well in the trans tunnel. My MJ is 2wd and I’m probably gonna leave it that way, so no need for a transfer case. Also, where would be the best place to buy a pre made harness?

bad_idea

I started down this path with an MJ not too long ago. I abandoned the project due to too many projects and only one of me. Before I kicked it down the road, I started digging into the wiring. When you pull the engine and trans out you can start pulling the Renix engine and trans harness. You will get down to two or three wires that connect into the body harness behind the dash. Basically keyed power and battery power. There isn't too much else that connects into the engine and trans harness. Get some wiring diagrams and start studying. If you can't read them, then learn - they aren't that complicated.

lawsoncl

The stock AW4 transmission has it's own computer and wiring. It needs inputs from the throttle position sensor, brake pedal switch, neutral safety switch and it's own output speed sensor. Note that on the Renix, the TPS signal is backwards from normal which is why it has a dual output. The brake light switch is also backwards, which is why it too has a separate switch.

USN_JeepXJ

Unfortunately there is no plug and play solution out there. I had Novak rework a Corvette harness (along with reprogram a Corvette PCM) and that portion of the harness is standalone for the most part running in parallel with the XJ harness (full 97+ XJ conversion). I highly recommend not trying to integrate the LS1 into the factory wiring (other than ignition switch) and just running a stand alone digital cluster. Way easier than doing what I did. Getting everything to talk to each-other required many weeks of pouring through the wiring diagrams of a 99 XJ, 99 Corvette, and a 89 MJ... In the end I have a fully working cluster (99 TJ cluster), air conditioning, and, hopefully soon, cruise control (99 WJ steering wheel... still working on that one) but it was a massive headache! The swap itself is actually pretty straight forward other than the wiring unless you're trying to adapt the MJ drivetrain... I'm running a AX-15 which was another adventure to make work.



I'm running a Novak module for the cruise and tach and Dakota Digital module to reverse talk to the Corvette PCM for speed. Additionally I added a XJ temp sensor into the radiator and a XJ oil pressure sensor off of the block. In the OBDII Jeeps, those signals are all sent to the XJ PCM and a multiplex signal is then sent to the cluster which necessitates the running of the XJ PCM. Pre OBDII I think the gauges all take inputs directly from the sensors so that may not be as big of a deal to get working. Regardless I still recommend just going with a stand-alone gauge cluster that plugs directly into the LS harness OBDII port as that avoids the headache of getting things to work. Gauges all working as they should:

That Jeep Guy XJMJ

I dug into your full build thread on your through link. Very nice work! I dream of being that diligent with my projects. What's soo special about the 99 TJ cluster vs any other newer style xj cluster? I've searched and cannot make the connection on any relevance to using that one specifically - if there is one?

USN_JeepXJ

Nothing special other than I like the looks of the TJ cluster. Same year and engine TJ and XJ clusters are interchangeable

epitohm

If you buy an engine with an included harness, there are videos online you can follow along to trim it into your own "standalone". Takes some time and reading, but saves the big cost of a premade standalone. Plus your stock computer comes pre-tuned! (unless you're making some changes to the engine...) I put an LM7 in my MJ this year, most of the MJ wiring can go. Track down wires for lights and accessories like wiper pump and horn, Once you identify everything you need to keep, the rest can be snipped. You'll need to know how to do wiring anyways, because no matter what you buy, you still need to integrate starter signal, your fan situation, reverse light, cluster, etc. etc.

Fun fact, if you opt for a chevy NV3500, you can use the stock driveshaft still!

FletcherHubbards

What I did and is the easiest is using a stand alone harness from someone like Painless Performance Wiring. If not them, a local hot rod/custom car shop can so it for you