LED Dash bulbs

I ordered some LEDS and I am ready to install them. With respect to polarity, If using them for "idiot lights", how do you know they are working? In other words, I can easily see the turn signals, dash illumination lights, but what about the oil pressure gauge. I have a separate mechanical gauge as well but sometimes we are idiots!

Interesting question. The easy way is to go back to 194s for the warning lights. Not much point in LEDs there anyway.

Other than that, you would likely need to go under the hood and ground the sender wire to see if they come on.