2001 Mustang gauge cluster service lights are all out (and other problems)

I have a 2001 Mustang GT (automatic) and boy does it have problems. Let me start out with the biggest:

This car got flagged by a smog referee (CA) before I bought it last year, due to being straight-piped. I have solved that problem and have 4 brand new cats on my car, but when I went to go have it inspected the computer was a problem. Namely, the service lights are not coming on at all no matter what position the key is in. On or turned on, ABS, power steering, E-brake, TCS, O/D, CEL, etc. - none of them turn on at any point. I know it's not the bulbs because I have switched gauge clusters and the problem is still there.

Another oddity - the CEL was actually off while the car had straight-pipes, and zero codes were coming up. Despite this, it still failed the smog test with OBD2 being a data-fail. I don't know what the hell I can do at this point, since I've also had to drop in an 2004 engine due to the previous engine crapping out.

Some other problems I could use help with - sort of numb steering. I was told to have my rag-joint modified. Does anyone have a diagram or step-by-step list on how to improve it for improved steering feedback? Another problem I have with the steering is that there's a creaking noise at low speeds while turning (doesn't matter which way I'm turning). Besides this, I also have a steering/braking problem - previous owner stuck on Saleen calipers on the front, and as I'm turning at low speeds while braking, the brake calipers or something feel loose or jumbled for some reason. It's very noticeable.

One more thing - my O/D switch is busted since the previous owner had it wired out of the shifter like an idiot. I've now gotten a new shifter with O/D button, but my mechanic can't find the O/D wiring. Diagram anyone? I'm also having problems with the TCS button - namely that the light is off and I cannot disable it. Unsure what's causing that problem.

In terms of your no CEL while it was straight-piped, it's common for an aftermarket tune to shut off the rear oxygen sensors, so no CEL and associated code would be thrown.  That thwarted the emissions program in CT for a few years, but then they started checking for the rear O2s, and if they were off, the car failed emissions.

I see you're looking at getting another shell, and given the number of hacks you've seen on your car, that may be the best idea.

Yeah, it's just that I'm a bit broke right now and the cheapest mechanic in my area does the swaps for $1200 (engine, transmission, and exhaust)

You know of a way to get stock OEM computer flashing done without going to the dealership, by any chance?

Could you buy a off the shelf part? Is it plug and play?

The computer itself? Probably, but I don't know if it'd need a tune to be flashed to my VIN

I would recommend searching on a Mustang-specific site for each of your detailed issues.  I had a computer refreshed once at a dealer for a Dodge truck, and it was around $130. That's probably the easiest way to get back to stock.

I've played around with these cars some and can probably comment on a few of the issues. I used to live in CA and learned that playing around with mixing engines, ECMs, and emissions equipment becomes a frustrating and expensive game. While engine hardware from 99-04 is all very similar you still have to deal with the PATS system. IIRC those cars don't play nice unless they have a paired ECM, gauge cluster, and ignition switch (or at least the transponder ring). I don't recall if the stereo was tied into that system as well. You can get the dealer to reprogram the ECM to the existing PATS system but it can get complicated fast if things aren't matching the original VIN.

Steering could be a few things but my Mustangs have always felt a bit sluggish. Check for play in the steering column linkage and tie rods. Steering racks can also get sloppy with miles. The creaking is likely the steering rack bushings. There was a TSB for the New Edge mustangs regarding that issue. You can fix it with aftermarket bushings pretty easily. No clue about the loose brake calipers...need some more information to make sense of that one.

Can't help with the overdrive switch either...never even driven an automatic Mustang.