I have a 2005 that I purchased a year ago. I noticed there where some electronic add on the car but I believe it was pulled out. The harness is still there, along with a relay switch that was not grounded, but wanted to know what you think it was used for?

I posted pictures near the ECU and thanks,

 

A quick google search on hwaxe04b it seems to be for some alarm/remote start module.

 

Flanders thanks for the info.

 

Seems a lot of people do this stuff....

When we bought my fiances used Mazda 3 a few years ago with only 18k on it, it had an aftermarket alarm installed....Total piece of garbage too....Would go off randomly, shut down the car, go off while driving, go off at night. One night I finally just got under the dash and unplugged everything and left it kind of in a similar state that yours is in. Car still runs fine with no issues years later.

I was considering removing the wiring, but it's such a rats nest I don't want to start messing with it. I'd just leave it.

 

I was trying to get in there and hook up my Yellow Jacket speed adjuster. I left it up there with some zip ties, I was afraid of yanking it all out and cause my car to not start.

 

+1 on leaving it lol. Assume that's the plan anyways.