How to find power for alarms?

[vancouverbc]

I'm looking for a constant plus wire. I know you stab them with test light to see which has constant power but is there more to it. I mean, do you just plug into any circuit at random?

[vancouverbc]

I'm installing keyless entry. Don't you have to worry about too many amps on a circuit?

[vancouverbc]

I have a lot of background with AC but have forgotten it. I found all kinds of constant+ when i removed panel under steering wheel. There was one that was dangling there from an alarm that i did not know about. Black widow is written on one alarm box. There are two alarm boxes and they both blink. A black and red wire are dangling hot. There is a grey wire with some kind of sensor on the end.

I hate just splicing wires together. It seems so amateurish. I think i will get some kind of connections that crimp. I don't know how to connect wires to the relays. The solder won't hold.