Wipers quit working low speed & delay, wont park. work fine high speed. have changed sw, didnt help

You didn't take into account the wiper switch is a input to the BCM - body control module ,or do you know that ? The BCM controls wiper one an wiper two relay's to turn on the wipers .
Wondering if it is the PCB or perhaps a physical problem? Guessing never finds the problem . Reading how they work in factory service repair info should be the first step for someone that doesn't know .
Intermittent Operation
Windshield wiper DELAY operation is a low speed wiper motor function with a variable delay interval between the wiper motor cycles. The DELAY interval is determined by a series of 5 resistors within the wiper/washer switch. During DELAY wiper operation, the signal circuit voltage is further reduced through the DELAY resistors. The body control module (BCM) monitors the voltage on the signal circuit to determine the delay interval between the low speed wiper motor cycles.
If the wiper switch is moved from a longer delay interval to a shorter delay interval, the BCM will command an immediate wipe cycle and reset the delay timer to the shorter delay interval.
Additionally, intermittent wiper operation is vehicle speed sensitive. As vehicle speed is increased or decreased, the wiper interval will also increase or decrease.

Low Speed Operation
When the wiper switch is in the Low position, voltage is supplied through an internal resistor to the signal circuit. The body control module (BCM) monitors the windshield wiper switch signal 1 circuit and energizes the wiper 1 relay which will operate the windshield wiper motor. The wiper motor will operate at low speed, since the wiper 2 relay is de-energized. Low speed can also be commanded with a scan tool by commanding Wiper Relay Cmd. ON and OFF.
High Speed Operation
In the High position, the windshield wiper/washer switch supplies voltage to both the wiper 1 and wiper 2 relay coils. This energizes both relays and allows battery voltage from the wiper 1 relay switched output to the switched input of the wiper 2 relay through its contacts and out the switched output of the wiper 2 relay to the high speed circuit of the windshield wiper motor. The windshield wiper motor will operate at high speed. During HIGH speed wiper motor operation, the wiper switch signal circuit is at the LOW speed signal voltage, and the body control module (BCM) supplies redundant voltage to the wiper relay via the wiper diode.

Wiper/Washer System Components
The Wiper/Washer System consists of the following components:
• Windshield wiper/washer switch
• Body control module (BCM)
• Wiper 1 relay
• Wiper 2 relay
• Wiper diode
• Windshield wiper motor
• Windshield washer pump
• Windshield washer nozzles
• Windshield washer solvent container
• Windshield wiper arm and blade assemblies
• Windshield wiper transmission
• WIPER/SW 10A fuse
• WIPER 25A fuse
Refer to Master Electrical Component List.

DTC B3715 02: Front Wiper Relay Drive Circuit Short to Ground
DTC B3715 05: Front Wiper Relay Drive Circuit Short to Battery or Open

Your best bet , take it to a qualified repair shop.

There is a wiper delay module under the dash that has failed. Windshield Wiper Switch MOTORCRAFT SW-5665

If you are having problems with the wipers not wanting to park, that is usually the park switch inside the wiper motor. The low and interm speed settings could be the delay module which could also affect park.
You may need a shop manual to troubleshoot the circuits.

Replace the wiper module. Cardone at around $35-$50. This is the black cover under the hood, driver's side with 3 screws and about 4" x 4". Takes about 3 minutes to change.
A1 Cardone 81158PB Remanufactured Wiper Motor Pulse Board Module

check out light switch for return earth back to relays

To the best of my knowledge, no parts are available for this problem.
This will be a big hunt for you to try to get the help you need.
Try car parts stores, car dealer ships, then go to Amazon and finally e-bay.
Feel free to take any side trips you wish in the looking.
I have had similar problems myself with malfunctioning delay circuits.
Perhaps your best bet its to try to find an older mechanic who knows how to by-pass the problem and cut the delay out of the circuit.
God bless your search.

you will need a new washer pump that is located in the washer reservoir and a new wiper motor cover which has the circuitry for the delay wipers. All you do is change them out with new parts and it will operate like new again

its the fuse inside the fusebox under the hood. the box is right in front of the battery. I had the same problem. 4 dollar part. look it up in the owners manuel and your good to go.

I had this problem (wipers only work on high) with my 2002 Chevy Malibu and had to replace the 6 amp diode (22059733) on the wiper control board. It is connected to the back of the wiper motor and is held on by 3 torx screws.
Radio Shack has them for $2.75 6A, 50V Rectifier Diodes (4-Pack) Model:276-1661