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LEXUS 1UZ-FE Engine Swap My blood sweat and tears. It will be worth it!!

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  #1  
Unread 02-07-2010, 07:55 PM
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Default Alternator Wiring Lexus Alt to Tacoma Chassis

Boy where do I start on this one? I plan on spending some time sorting this out for all the other people who might run into this same task. Sounds easy right? We just want to connect the power generator / alternator that is on our Lexus 1UZ-FE to the chassis electrical system of whatever vehicle we are putting the engine into. In this case it's my Tacoma. Big surprise.
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Unread 02-07-2010, 09:48 PM
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There is so much information on this topic that I have it's hard for me to begin. I'll start with posting pictures of each wiring diagram from both vehicles so you can get an idea of what I'm dealing with making this 1UZ alternator power the 1996 Tacoma chassis wiring harness that I put the engine into.

But FIRST, just to clarify most cars have a chassis wiring harness that controls all the lights, alarm system, accessories, all the lights and everything except the engine. This wiring harness is powered by the main fuse and relay box. This means that you might have some starting relays, engine fuel injector and fuel pump fuses in the same box as well. This central power box is powered directly from the battery which powers the whole vehicle. The alternator on the new engine must be properly connected to keep the batter charged through this power box.

Then you have the engine wiring harness that controls the whole engine, emissions and fuel pump that plugs into the ECU right next to where the chassis wiring harness plugs into it. This is tossed aside with the old engine.

And with your new engine comes a new engine wiring harness.

So with some work and custom wiring you can put in any engine BUT you have to change a couple of wires around so that the new engines alternator will power the chassis fuse and relay box. I call this the power box because all the main fuses for my vehicle are contained in this with the main relays for the starter and stuff.
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Unread 02-07-2010, 10:08 PM
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Lets begin with the nice and simple 3RZ engine starting and charging diagram for an older Tacoma.



When you look at the alternator plug from the little 3RZ engine it has 3 small gauge wires that are red, yellow and white. Then there is a larger gauge white wire that is the main power wire that bolts to a terminal on the alternator and goes directly to the power box's 120amp fuse which links to the battery.
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Unread 02-07-2010, 10:21 PM
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You will notice how the diagrams have changed a little bit in terms of the way they lay it out from the older Lexus SC400 electrical wiring diagram compared to the newer Toyota Tacoma electrical diagram. One is definitely a little easier to understand.

The same components that are displayed on one page in the Tacoma manual are shown across two pages in the Lexus Electrical Wiring Diagram book. You will notice that both the Black/Yellow and the Yellow wire stop short and you are told to refer to the page 56 where they continue to be shown.



Here is the next page showing where those two wires continue on in the diagram:
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Unread 02-07-2010, 10:32 PM
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Now this is where things get complicated just a bit. The Tacoma alternator plug has three wires (R, Y, W) coming out of it and the Lexus alternator plug has more wires of different diameter.

And also you have to realize that the chassis wiring harness is composed of all the accessories the vehicle might have. In the case of my Tacoma I have a radio in the cab and a couple of lights. No power windows, no power locks or any of that monkey business. Then the LS400 is totally the opposite and it has every accessory under the sun including a power hungry stereo with amps. The two chassis harness require COMPLETELY different amounts of power from the alternator. Thus you can see that the Lexus alternator is looking twice as big as the tiny Tacoma 3RZ unit.

So can you guess how much power is needed from each alternator? You can imagine the difference. Now you have to look at the fuses which tell you how much power is the maximum power needed before the main fuse in the circuit blows. When a fuse blows it means that much more power than usual is being consumed by the circuit. It doesn't mean there is a SHORT in a wire but this just happens to be a common cause of too much power being drained through the fuse to the point at which is will burn out. We just need to realize how much power each system is designed for and this will help you understand how the power flows. If you just look at each fuse and hook them up because they match then it will be wrong because the vehicles power systems aren't the same (which obviously means the fuse denominations will be different even though they do the same job but under different loads).
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Unread 02-07-2010, 10:38 PM
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More to come... I told you there was a lot coming. =]
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Unread 03-09-2010, 10:37 AM
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I have been reading your post on the forum about swapping in the lexus alternator. Thanks for posting the wiring diagram. I am doing a little different project of putting in a tacoma 3rz motor into a series land rover (1969). I am trying to figure out what I need to connect the three wires of the alternator to. Are you getting rid of the old 3rz battery harness, that connects the starter-alternator-battery? If so, would you be willing to sell it? My swap involves using the Offroad solutions 3rz conversion harness, and a painless body harness, and a existing 3rz motor harness. The instructions call for using the existing battery harness, but I dont have it. Or if you know how to dumb down the 3 wire alternator that would be great as well. Sorry about the random hijack, but every google search I do, comes to your post. cheers and thanks ian
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Unread 03-09-2010, 04:44 PM
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Dude, you got it made. It's no big deal. I'll take pictures of my alternator harness from my 3RZ and post it for you. You can make your own in about 10 minutes. I'll get back to you when I have a chance. I'm sure more people have the same questions and having the basic wiring here in this thread will be a good thing.
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Unread 03-10-2010, 05:57 PM
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thanks a bunch. great forum
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Unread 03-10-2010, 11:50 PM
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I just keep it nice and simple. I made a note to get the info for you tomorrow so stay tuned.
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Unread 03-13-2010, 10:04 AM
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Here is the factory wiring... seriously this is it. This is what connects the alternator from a 3RZ Tacoma engine to the electrical system of the 1995.5+ Tacoma. You can trace the three colored wires in the wiring diagram earlier in this thread or I can find the pictures of when I cut them from the plugs to use them for my swap. Told you it was easy!


Last edited by Smithers; 06-16-2011 at 11:11 AM.
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Unread 03-13-2010, 10:10 AM
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I've kinda neglected to finish this topic as my 1UZ alternator is working perfectly now. The funny thing is that I assumed the alternator that came with the engine was working fine because it was operational when the car came to the end of its life (right? : ). So when I was trying different ways of hooking it up I just stepped back and said, "what the heck is going on here... it shouldn't be this difficult!?". So I thought yeah... just my luck this alternator is a gonner. I took it to have it tested and sure enough... bad. So here is another example of "this engine swap is costing my MUCH more than I thought it would..." and I thought it would cost me 2x what I originally estimated... try 5x more.

So another $200 later and I have an awesome alternator now. It came from Carquest with a test sheet that proclaimed the company works hard to manufacture quality alternators and they stand by their product. Plus on the sheet they also show the individual alternators bench test results and a little graph showing how well it puts out. Hehe.. puts out.

If you get an alternator for less than $200 I would be concerned... that's just too cheap. You just can't get a quality product for under that price. And when you buy at Carquest it's satisfaction guaranteed and they stand behind that alternator for LIFE. Seriously it's true. If this thing ever goes out... I get another new one for FREE. Same with the starter!
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