I'm installing my old Bulldog Keyless entry on my sister's 94 ST, and I asked went to RadioShack and told them I needed 2 12V 1AMP Diodes (that's what I used on my car, and re-used them when I bought an alarm) they didn't have 1AMP in 12V, so I got the biggest they had, 21mA which is a lot smaller than 1AMP. I really don't feel like going out and hunting down 1AMP diodes.

My guess is it will render one of those "Don't lock your keys in your car" features useless. If I absolutely have to, I'll get 1AMPs but it's not a big deal to me, lol.

What will happen if I use the smaller ones?

i'm confused what you are trying to do... if you use a 21mA diode where a 1A is called for you will most likly burn the diode up. if you are just trying to isolate a circuit, meaning current will only flow in one direction then you just need a PIV rating of higher then 12V and a current rating higher then what will flow through that wire. just go try a 1n4001 (PIV: 50V, Imax: 1A) they cost about 10 cents.

What are you trying to diode-isolate?

The door triggers aren't separate so there is nothing to diode-isolate on the Celica. A lot of GMs the door triggers are separate so this is necessary but in our case it isn't.

No, all of you misunderstood me. I know diodes only let power feed one way and I was under the impression that the unlock wires going from the alarm brain to the door control module had to be diode-isolated. It says this in all of my alarm instructions and it also says it in the alarm install guide. I used 1AMP on my car, and used 21mA on my sister's 6GC, and it worked fine, no problems after a thorough test.