Battery Disconnect, Knife-Switch

I purchased a knife-switch type kill-switch made by the Wirth Co., for the battery on my '99 Merc Grand Marquis. The instructions say to install it on the NEGATIVE post but, I would like to install an other one to the POSITIVE post as well, because my car's manufacturer states that BOTH + & - posts be disconnected, when servicing electrical components (esp. re: possibility of accidental airbag discharge). It is a bit of a pain in the rump to have to unscrew the batt connector from its post EVERY time I have to service an electirical component-- aside thewear & tear it dies to the connector & bolt: Is there some reason that I should not install another one on the positive-side?; or should I just use the knife-switch on the " - ", and just disconnect the " + ", when working on electrical components?
AGAIN: The manufacturer (Ford = Mercury) states that BOTH "+" AND "-" be disconnected, to insure airbag dis-connectivity.

so long as you are NOT working on the dashboard, disconnecting only the negative side is sufficient.
For dashboard or steering wheel work, obviously disconnect both.

As for the switch... it may not be properly insulated for use on the positive terminal. It's possible it may have exposed metal part(s) which may represent an electrical hazard if hooked up that way.

the switch... it may not be properly insulated for use on the positive terminal. It's possible it may have exposed metal part(s) which may represent an electrical hazard if hooked up that way.

Thanks for the advice, M.R.!
Indeed, the switch is composed almost entoirely of metal [here's a pic] http://www.jcwhitney.com/wcsstore/jcwhitney/images/imagecache/G_16121G_CL_1.jpg
At risk of showing (more of) my ignorance/beating a dead horse, seing as-how it appears that the switch is NOT well-insulated, what electrical hazard might that pose?... More likelyhood of pos. charge touching frame or other ground-- Arcing from positive to frame(???)
Thanks!

If the switch is installed on the negative side, when the switch is open, there will be no closed circuit to ground. Therefore, if some device that is connected to the positive terminal touches to ground while the switch is open, the circuit will not be completed and nothing of significant current-storage capability will be shorted. However, you'd certainly want to make sure such a short is not currently present when you flip the switch back to closed.

The other risk would be if you drop a metallic tool/object on the switch while the switch is open and you're working on the car.

Do you really service electrical parts on this car so often that you can justify this effort?

-Rod