Just a bit more info- - - -the GM original equipment switch is available, but it's ridiculously expensive- - - -something like $85.00 USD. The aftermarket parts source is "Standard" brand, part number VX2. It's about $35.00! Here's a link from Rock Auto, if it will work:

STANDARD MOTOR PRODUCTS Part # VX2 {LOCK-UP TORQUE CONVERTER SWITCH}
Category: Auto Trans Lock-Up Torque Converter Switch
* Non-stock item--shipping delayed up to 2 business days
$35.79

I used a reference for a 1981 Impala, 305 engine, "automatic transmission parts" on the Rock Auto website.

Have fun!
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!