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Awesome that is was that simple/cheap. Looks 100% stock. Nice job.

This is really awesome! I am so glad you posted this! You are giving me terrible ideas!

So how did the wiring go? You said modded fuse box connector? Was there any mods to wiring or any issues?

What year did you use? Any year 00-05 should work as a donor correct? Or does the donor have to be the same year as the cadillac?

That is awesome!

Looks like some good work! Completely OEM.

Thanks everyone.
94silverSSEI, I had to change the insulator for the engine harness to match the Caddy
fuse box. One had the bolt in the insulator, the other one the nut that mounts it. I was
able to make the car run and drive after just switching the insulator(moving the wires).
There is wiring in the Caddy harness the Bonne harness doesn't have. ABS wiring mostly.
The ABS module is dead on the Caddy so I didn't bother.

Oh, and I used a 2001 SSEi harness. I imagine '00-'03 would work.

I'm in the "That's friggin Awesome!" camp! Well done!

l67se wrote:Thanks everyone.
94silverSSEI, I had to change the insulator for the engine harness to match the Caddy
fuse box. One had the bolt in the insulator, the other one the nut that mounts it. I was
able to make the car run and drive after just switching the insulator(moving the wires).
There is wiring in the Caddy harness the Bonne harness doesn't have. ABS wiring mostly.
The ABS module is dead on the Caddy so I didn't bother.

So did you have to have a manual for each and actually repin the harness? I'm not sure exactly what you meant by "switching the insulator"? So the ABS won't work with this swap or you are unsure as your ABS was dead? I was very much interested in doing this swap into a 98-03 seville. But I was unsure of the wiring/electronical part. What year was your seville? Also is yours an SLS or STS?
I would prefer an STS but I know it has more electronics that could be come an issue?

My Caddy is a 2000. It's a SLS.
The wires for the fuse box side; I just moved them from the Bonne plastic insulator
to the Caddy insulator so I could mount the insulator into the bottom of the fuse box.
The wires went into the same slots that they came out of. I did have connector pinouts
for both cars that I pulled from alldata.
There were 4 wires for the ABS that ran from C101 to the ABS module on the Caddy that
the Bonne harness didn't have. I added those wires to the Bonne harness (can't remember
what they were for right now) but the Caddy ABS still didn't work. I had checked the power
and grounds to the Caddy ABS and they were good. I assumed the ABS module was dead and
didn't bother pursuing it. So I couldn't tell you for sure whether the ABS was dead already or
the swap somehow caused it.

My SLS is fairly loaded. The only options it doesn't have is the sunroof and rear park aid. I imagine
there wouldn't be anything over and above on a STS that might cause issues.

Ok thanks for the help!

I happen to have an 05 Deville at the moment and I'm 99% sure it has bad headgaskets wonder how similar the seville and deville are? It's an extremely base deville. Has no options. I think it should swap no issue?

During my junkyard runs for a breather that would fit the Seville and 3800, I found that the Deville was much closer in match to the Bonneville. A/C lines route the same so I don't think the condenser would need replaced. The accumulator is in the same place also. On the Seville, I had to move the accumulator(and use the Bonne accumulator) to the engine side of the fuse box to get the 3800 A/C lines to match up.
I just did a quick check on wiring connectors and it looks like the Deville has the same setup. Fuse box for one side of the engine harness and C101 for the other. Definitely looks doable with minimal issues. I imagine since it's closer to the Bonne setup, that the overflow tank and breather from the Bonne would work too.
I couldn't make the coolant overflow from the Bonne work for the Seville since it was on the passenger side and the way the fuse box and A/C lines routed on the Seville, there was no room for it. The overflow (driver side mounted) and breather from a Park Ave ('02 IIRC) fit perfectly.

I had to extend the magnasteer wiring on the Bonne harness because the Seville harness plugged in at the steering gear. The Bonne harness plugged in near the passenger side of the steering gear. I also remember having to do something with the passenger front ABS sensor connector but for the life of me, can't remember if the Bonne harness needed modifying or if it was just damaged there. You'll also have to do the "learn" for the Bonne PCM once it's in the Deville. Key on till the security light goes out on the dash (approx 10 minutes) cycle key off, back on twice more (30 min total time) to get the Deville to recognize it.

Basic parts list (off the top of my head)
Complete 3800 Bonne drivetrain including mounts and exhaust down pipe
Bonne 3800 radiator, radiator hoses and heater hoses
Bonne engine wiring harness and PCM
Bonne 3800 power steering hoses

Can't think of anything else you'll need at the moment.
I'll be happy to help any way I can if you decide to do the swap.
You can PM me for my email

Hmmm. Well I already have the 05 Deville which I originally bought for my grandmother but its too big and then was going to be a swap but I'm thinking this would be a fun project. Never put an engine in something it didn't come in.

Well I've run across an 03 Lesabre with low miles that was in a bad wreck. I know an L36 Deville would be a turd but its such low mileage on the lesabre, its hard to pass up.


I've cross-checked part number and it looks like most all suspension components are the same. I'm wondering if it might be easier just to swap the whole subframe out of the lesabre into the deville? So you used the Cadillac steering rack then?

Checked the radiator and condenser and they show different part numbers but they look VERY similar so I think I would be able to reuse the one from the Deville as the donor Lesabre is whacked pretty hard in the front.


oh yes, I'm very familiar with the 30 minute relearn. I can't even count the number of times I did that on the last Bonnie.

Thanks I really appreciate the help!

I would have to say, GOOD JOB! and agree with Matt. - BC

Great post!! I run a small garage in the caribbean, one of my clients owns a funeral house and has a fleet of caddy's ranging from 1994 to 2004, this post just gave me a great project to work with him, he was excited to know that there is another option rather than the N*. With all the heat and at funeral speed they blow the gasket pretty quickly down here, next week im going for a swap like this one.

I can't believe I never saw this one after l67se posted. This is freaking cool.

I managed to do this swap and get the caddy running fine. So far everything seems allright. Minor details coming up but nothing important. Got 2 more caddys waiting for the outcomw of this one to do the same swap. Biggest headache was getting the passkey to work since the caddy had it override, nothing that some pcm reprogram couldn't solve

I'm just starting on this swap using a 2001 Seville STS and a 1999 Bonneville parts car. Did you guys that did the swap use the 4t65 or the 4t80 trans? I have both and trying to decide the best route to go. I'll be using the Bonneville ECM and engine wiring harness. It looks like if I use the 4T65 I'll have to build mounts for the Caddy engine cradle?

4T80 doesn't fit the 3800. Most of the stuff you need like the radiator, condenser, etc. needs to come from a '00 up Bonneville.
The 99 Bonne trans will need the side cover switched to an aluminum one so the side mount can be used.
You'll also have some wiring compatibility issues as the 99 trans uses an external P/N switch and the '00 up is internal.
I don't know if the 99 wiring harness will work without extensive modification since it doesn't have the C101 and fuse box connectors that match the Caddy.
This is what I can think of off the top of my head at the moment. It's still early and I haven't had a full cup of coffee yet..lol

Wow, didn't realize the differences would be that much in just one year. I guess a trip to the boneyard is in order to find a wiring harness. I'm thinking I can make the radiator work. So the side cover mount on the trans is the one by the rack n pinion?

Thanks for the help!

The 4t80 can be used, just have to grind a few tabs on it, I can point you to more details if you're interested.