I lost the instructions to program a Westek UMDW10 digital wall switch timer and can't seem to figure it out--help.

No, the wiring does not allow you to power a 12 volt load directly ... but you could use the timer ... 1) to turn the LED driver on-off ... or 2) to switch a small relay on-off, and use the relay to control 12 volt LED driver
The following page has typical programming and manual for this timer that is sold under several different brand names:
http://waterheatertimer.org/Program-wire-Utilitec-LW60418.html

http://waterheatertimer.org/Program-wire-Utilitec-LW60418.html
Westek TMDW10 is same as Utilitec/ probably made by Intermatic.

Gene
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If you need further help, I’m available over the phone at https://www.6ya.com/expert/gene_9f0ef4df2f9897e7

Need instructions

Copy following link to identify timer and download possible manual:
http://waterheatertimer.org/Woods-timers-and-manuals.html#Westek



2) Model number and timers change frequently.
If your timer does not show, then add a photo or comment with clear description of timer

If you need further help, I’m available over the phone at https://www.6ya.com/expert/gene_9f0ef4df2f9897e7

You have westek 7 day timer
Open following link to identify timer and read possible instructions:
http://waterheatertimer.org/Program-wire-Utilitec-0141224.html

If you need further help, I’m available over the phone at https://www.6ya.com/expert/gene_9f0ef4df2f9897e7

TE05W is a Westek timer.
Here is copy of manual:
http://waterheatertimer.org/pdf/Westek-TE05W-manual.pdf

Other Westek timer manuals:

http://waterheatertimer.org/pdf/Westek-TE05WHBL-manual.pdf

http://waterheatertimer.org/pdf/Westek-TM07DHBL-manual.pdf

http://waterheatertimer.org/pdf/Westek-TM07WHBL-manual.pdf

http://waterheatertimer.org/pdf/Westek-TM08DHBL-manual.pdf

Westek TE06WHB timer
Utilitec TE06WHB timer
Woods 59377 are identical timers
http://waterheatertimer.org/Woods-timers-and-manuals.html#59377

Woods 59377 manual
http://waterheatertimer.org/pdf/Woods-59377.pdf

Written instructions:
http://waterheatertimer.org/How-to-program-Utilitec-0155671.html

http://www.intermatic.com/products/timers/consumer%20indoor%20timers/in-wall%20timers.aspx

http://www.intermatic.com/products/timers/consumer%20indoor%20timers/in-wall%20timers/ej500c.aspx

http://www.intermatic.com/~/media/files/intermatic/products/instructions/timers/ej500c%20-%20english.ashx

Westek TE05W
http://www.alexfish.com/dload/Westek%20TE05W%20digital%20timer%20manual.pdf

Westek TE06WHB timer
Utilitec TE06WHB timer
Woods 59377 are identical timers
http://waterheatertimer.org/Woods-timers-and-manuals.html#59377

Woods 59377 manual
http://waterheatertimer.org/pdf/Woods-59377.pdf

Written instructions:
http://waterheatertimer.org/How-to-program-Utilitec-0155671.html