Well, since the newfangled web forum I posted to hasn't exactly bristling with answers, especially helpful ones, I figured the old tricks were the best and so I have returned. (Amazingly my ISP still has a running news server.)
I traded my 2003 Chevrolet S10 for a 2007 Silverado Classic (carryover body style) LT 4X4 pickup truck when the S10 dropped its fuel pump. I decided it had simply fallen apart beyond what I was willing to fix. Everything's been going well with the "new" truck, or rather, it was until a few days ago.
The trouble started when the Engine Hours counter in the DIC display reset itself to zero. There's no way to do this manually per the owner's manual, but nothing else was affected at the time. A half hour later, the ABS and Brake Fault lights came on, complete with lots of warning chimes. Not long after this I discovered that the blower fan did not function on any of the first four speeds. The fifth and highest blower speed works fine. All others will provoke the brake system warning lights and chimes at random. They'll also cause the cruise control to lose its speed memory when engaged. It then has to be reset.
No fuses are blown. I tried replacing the blower resistor pack to no improvement, thinking it might be an issue with the spike suppression diodes on that assembly. There is no burned wiring at the climate control head (manual dual zone), resistor pack or blower motor. Ground at the resistor pack tests good (zero ohms resistance between it and unpainted body metal). Volt meter shows 11.5 volts at blower motor terminals with motor unplugged and meter connected when control is cycled through the first four positions. Meter shows 11.8 volts at the highest fan speed position. (Engine was not running during these tests.)
I can't imagine the blower motor itself is bad. I'd expect it to overheat, blow fuses or not get up to speed if it was bad. It doesn't have a lot of inertia when spun by hand, but I don't know if a "known good" fan motor would be different. There is no unusual noise from the blower assembly that would suggest a bad bearing.
I noticed yesterday upon shifting into four wheel drive mode (floor mounted shift setup) that the four wheel drive symbol in the instrument cluster did not light (despite the truck very clearly being in 4WD mode) and the ABS/brake failure lights once again came on.
This really seems to me like it should be a ground problem, but I sure haven't found a bad ground.
Any thoughts? Help would be greatly appreciated--driving around with the blower on high all the time is getting old!
William