1998 chevy blazer windshield wipers intermittent, already replaced pulse board

I have a 98 chevy blazer with the age-old "intermittent wiper" problem, which seems to be a common problem. Apparently just as common is the prescribed fix: to replace the wiper control module circuit board (the pulse board). However, I already replaced the pulse board but still get the same intermittent behavior...

I've also tested the voltage at the yellow and purple wires on the 5-contact connector that plugs in to the pulse board with normal results (I think): ~12 volts on the yellow wire always, and ~12 volts on the purple wire with the wipers set to "high". Any ideas what steps I might take next to debug this thing?

Yellow wire should be hot in the accy and run position. The purple wire is high speed, the grey wire is low/pulse, the dark green wire is mist only, (momentary). The black wire is the ground for the motor and the logic module, (pulse board). Unplug the connector and make sure resistance on the black wire is less than 5 ohms to ground. Try wiggling each wire with the voltmeter connected and watch for drop outs. Could also be a problem with the switch or a poor connection between the switch and the logic module.

Thank you for your response, it was very informative and got me started in the right direction. It turns out the problem was pretty silly, after some fiddling I discovered I could get the wipers to work if I put pressure on the pulse board connector at the right angle. Upon further inspection I figured out that the two little leads on the pulse board simply weren't making good connection with the little plate behind thecircuit board. After bending them up a little further it's working perfectly. Such a simple fix, but such a headache :-) I guess at least I learned a lot in the process :-)

Just curious, how did you know what the signals on each of those wires meant?

Another thing (slightly unrelated, just curious), I was thinking I could just short the purple wire to the yellow (12v) to turn the wipers on "manually" but it didn't work. Whjy would that be? Is the purple wire actually carrying a pwm signal or something?

multifunction switches are commonly a source of problems on blazers.

Wiring schematics are a beautiful thing ;)

The yellow wire in the electrical connector of the pulse module supplies battery voltage for the motor through fuse #17 in the instrument panel fuse box. Depending on which one of the 3 wires from the wiper switch sends a signal to the module, the module operates a relay that connects the yellow wire to the motor itself. With the pulse module connected and the ignition on, applying battery voltage to the purple wire should operate the wiper motor. The wiper switch gets its power from the same circuit that supplies the wiper motor, (the yellow wire). The switch sends battery voltage to the pulse module, nothing special about it, no PWM is used.

Nice, thanks for the tips. It just hit me why shorting yellow to purple wasn't operating the wiper -- the same reason it wasn't working from the multi-function switch! I hadn't bent the leads up at the time I tried shorting them together... Duh!

Thanks again!