Pad Sensor Info / Pad Replacement
The sensors are a loop of wire that run through a bit of metal (it maybe brake pad material actually) that slots into the top of the pads. As the pads wear past 70% (roughly) the metal starts wearing away. Once the metal wears away the insulation on the wires gets eaten and when the wire loop itself wears and breaks you get the warning light. You'll have to replace the wire itself. As I didn't let mine get that far I can't advise on exactly how to do that. I suspect that the entire wire (about a foot long) needs to be replaced. Talk to Dave Roberts he can fill you in on the rest and get the parts to you.
As far as doing the pads is concerned the shop manuals have an easy to follow procedure. You'll need new pads, 16 damper plates AND a means of bleeding and/or flushing the brakes and slave clutch cylinder when you're done. The really frustrating part about the pads is getting the sensors out without damaging them. However, for at least one of your calipers that won't be a problem.
Piece of cake, the pads have a notch on the top where you insert the 'sensor'. You're right too, once the sensor is worn away, it's time for a new one. They are cheap though. Phil's tip is to get the dual sensor loop, that way you can watch both pads per side and not just either the inboard or outboard pad. I don't know when the change was made, but the GT and certainly the GTS has dual sensors per rotor.
If you ever wish to circumvent the brake pad wear warning you need to connect the wires that go to pins 19 and 20 on the black plug to the central warning unit. If you orient the plug so that the alignment tabs are upward, the pins read left to right as 14 to 25. The central warning unit is located under the "dead pedal" (just to the left of the clutch.)
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