Brakes ABS Module Light is on constantly-HELP!

[99 FLA PONY GT]

Has anyone had this problem of having staggered tires causing the ABS light to stay on. If so, how did you correct the problem?
I'm the original owner of a 1999 Mustang GT automatic with traction control.
The car came with 245/45ZR17s all around.
I now am running 245/40ZR18s up front and 295ZR18s in the rear.
The ABS light has been on for years and when the problem first appeared I took it to a local Ford dealer and they wanted $800 to replace the ABS module. I said screw it, I'll drive with the light on. Well I now am annoyed at looking at the dash and seeing the ABS light on and also traction control being off.
I went and got a used ABS module and the light was out for a day and then it came back the next morning when I started the car. The mechanic said the ABS module he put in is good and that it's talking to the computer and it's telling him that the right sensor is bad. The mechanic also said that replacing the right sensor may not correct the problem. My problem according to him is that the wheels and tires are 2 different sizes and it's throwing the ABS module off. He said that on the '05 and newer cars you can enter your new tire sizes and it would allow you to go forward w/o the light coming on.
Thanks in advance.

 

[Kilgore Trout]

Try cleaning the problem sensor.

 

[99 FLA PONY GT]

Sensor is cleaned and still lights on. If I replace the so called bad sensor do anyone thinks my problem will be solved?
Has anyone encountered this ABS problem running different size tires?

 

[gearheadboy]

Yes running tires that are different heights can be a problem. The computer sees vehicle speed at each wheel and determines that the wheel speed is correct. What I would do first is see what code it sets and perform the appropriate diagnostic. It could certainly be a bad wheel speed sensor. A sensor can be tested by measuring the resistance in comparison with the other one from the other side. Also I would check for AC voltage in the sensor connector when spinning the wheel. A slightly different tire size will work but a large height difference will not.

 

[bullitt 736]

You've got 0.4" difference front to rear which for many has not been a problem. Double check your sensors before anything else.

 

[joshjwc9]

Going through this right now. My light will come on temporarily for about 5 minutes and 3-5 miles then go out until the car cools off. I replaced my module (which was a Cobra, although my car is a GT) and still no change. My car is either a Monday build car or something, but I've never touched the module since I got it with 68k miles and no ABS light until now at 160k. There are modules on eBay for cheap and you can do it in about 2 hours with some beers, or you can remove the module, still drive your car and have it repaired for about $100.

 

[bquinlan]

Going through this right now. My light will come on temporarily for about 5 minutes and 3-5 miles then go out until the car cools off. I replaced my module (which was a Cobra, although my car is a GT) and still no change. My car is either a Monday build car or something, but I've never touched the module since I got it with 68k miles and no ABS light until now at 160k. There are modules on eBay for cheap and you can do it in about 2 hours with some beers, or you can remove the module, still drive your car and have it repaired for about $100.

Did changing the module fix your issues?