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FrankenHummer Build

AutoJunky

Member
Messages
21
Location
Utah
Hey Everyone,

I know some of the information that I am hoping to get from this post has been covered somewhat in other threads but they are all from a number of year ago so I thought I would see if there is any new and updated information that all of you might be able to help me with.

I am a relatively new Hummer owner. I have owned an 08 H3 with a 6 speed manual in the past, but now I am the proud owner of an 05 H2 and a 06/08 Hummer H3 Alpha.

The H3 that I had in the past just didn’t have enough power with the l3.7 so I have been keeping my eye open for quite some time for an Alpha. I was able to find a wrecked Alpha on auction and got it for a pretty good price. The front end was toast on it however so I also bought an 06 H3. My plans were to swap the body from the 06 onto the 08 and have me a clean title FrankenAlpha.

I did the swap. The body swapped over very simply. Everything bolted right up. The 06 radiator matched with the 08 Alpha radiator. Really the body swap went so smoothly I was quite surprised. I can see where you all have mentioned that the 06 vs 08 body is tighter on the firewall at the back of the intake on the 5.3l but the Alpha had a foam pad on the back of the intake and that pad just barely rubs the firewall so I don’t think I have any issues there.

So, now to what I am hoping to receive some expert guidance on. I didn’t do my research enough on the wiring. I think if I had swapped an 08 body onto the 08 Alpha my life would be a bit simpler, but with the 06 body the wiring harness from the engine and ECM don’t match up well enough to the harness going up the body of the 06. I am hoping some of you will have expertise or know someone I can contact to help make a custom harness of sorts to simply pair the engine ECM harness from the Alpha to the body of the 06.

Worst case scenario is I strip both H3’s down and swap the entire harness from the 08 into the 06 body, however that is more work than I really want to tackle if there is a more simple solution.

Thanks!
 

JPaul

Well-Known Member
Messages
2,400
Location
Way up north, UT
Good question. The ECM's changed between 06 and 08 so I'm not sure if you can simply get an adapter harness or anything like that without having to either custom make one yourself, or get a harness for the 06 ECU to interface with the 5.3 engine and get the computer reprogrammed (which generally is what everyone that does a V8 swap into the 06/07's does). The 08+ PCM is two units, one for the engine and one for the transmission, whereas the 06 ECU is a single unit for both engine and trans. I'd have to look over the schematics as well to make sure there aren't any differences in the body harness itself between the model years, there very well could be.

Frankly since you already have the parts I would just gut everything and swap the harnesses. Far better (and much cheaper in this case) to stick with OEM than trying to use swap harnesses. Plus then you can really go through everything and take care of any issues and get the interior all cleaned up. Just make sure to take lots of pictures to record how everything is run. Yes, it's a ton of work, but personally I find it worth it in the long run. My Alpha has been down for weeks now just while replacing the cooling system on it. Right now I am actually waiting on the bushings for the lower radiator mounts since the new radiator didn't come with them and the old ones are starting to break down. Of course they're on backorder so I may just put the old ones in for now, but I'd feel a lot better with brand new ones in there. Do it right the first time or regret it later when you have to fix it again.
 

AutoJunky

Member
Messages
21
Location
Utah
I agree probably the “right” way to do it would be to just swap the entire harness over. I guess at this point I shouldn’t be lazy since I’ve already gone as far into the project as I have. Once concern I have is that some of the wires from the ECM running into the dash on the wrecked body were broken or cut somehow. I’ve heard that splicing the wires back together sometimes gives incorrect resistance readings and can cause havoc. I am not great at the wiring stuff so I’m doing my best to learn as I go.
 

amrg

Well-Known Member
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2,317
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Qatar
Trying to adapt the 06 / 08 harness will be a pain since as said earlier, the ecu was updated from a single unit to 2 specific controllers. This will require you to open up the harness and seperate the engine from the trans, then pin each wire to their corresponding locatiok in their corresponding connector. Not difficult, but its work.
You will also need to add a ISS wire as the newer TCM requires one to monitor the input speed at the transmission, otherwise you may go into limp mode
 

AutoJunky

Member
Messages
21
Location
Utah
I am using the original ECM off the Alpha so it should already have the controller for the engine and trans set up as it should be. Unless I’m understanding things incorrectly I just need to adapt the connection on the ECM that runs into the cab through the firewall. For the most part all of these wires have to do with sending error codes and info to the instrument cluster, reading the gear position, t-case shifting, AC pressure etc. There are a couple wires from the 06 that have to do with starting/charging that I don’t know where they trace to. I’m sure I’d have to take things apart still to track wires and put them in the right place, however my know how for such things is lacking. The other thing I’m not positive about is the anti-theft security and whether or not it will shut off my fuel because the body is not the original paired to the ECM.
 

JPaul

Well-Known Member
Messages
2,400
Location
Way up north, UT
Yeah, just swap the harness and be done with it. I can only picture many frustrations down the road otherwise.

As for the broken wires, as long as the crimp is done correctly there won't be enough of a voltage drop to affect the readings. You'd have to have a pretty sensitive meter to detect the minuscule voltage drop once the crimp is done. Use quality and properly sized barrel crimps with adhesive lined heat shrink and a proper ratcheting crimper. You should have no problems at all with it. It's when cheap crimps are used or poorly done and the connection isn't solid that you'll see issues. You might get the suggestion to use solder, but truthfully that is a bad idea for something like this. A mechanical connection like a good crimp is far superior to any soldered connection for several reasons, including durability of the joint (a soldered joint can result in stress failure of the wire right where the solder ends if there is any vibration or bending forces applied), conductivity (solder has lower conductivity than copper, and a good crimp is actually mechanically fusing the two sections of copper together, even if it's a bridge like a barrel crimp.), and longevity (solder, particularly lead free solder, can go wonky over time due to the inherent design of the metallurgy of the solder alloy and the environment it is in).

If you do decide to go with soldered joints, you really need to make sure to do them correctly, which involves twisting the wire ends together to first form a decent mechanical connection that the solder then just holds together. You also only want to do them when you can ensure that the joint will never, ever bend or freely vibrate. And you must use adhesive shrink tubing to seal the joint and help keep it from moving too much. The problem though in this situation is you typically don't have any extra length to work with in the harness to shorten one or two wires by even a half inch. Crimping with barrel crimps allows you to keep the wires the exact same length so the harness won't get all wonky when you try to route it in the stock position. They do add a bit more bulk to the harness but as long as you don't have more than a few wires to splice in that particular spot it should not be an issue.
 

AutoJunky

Member
Messages
21
Location
Utah
Thanks JPaul. That is good information. I have always thought that solder was the way to go. Looks like I need to go invest in some good crimpers and barrel connectors. After the research I’ve done and thoughts from guys here on the forum I’m planning on getting the harness stripped out of the wrecked Hummer this weekend so I’ll fix those wires once I get it out.
 
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