Remote Start isn't that hard.....
I'll break down the wiring (without colors, but if you post year and any options up until like 98 i can get you exact colors), and the install.
FIRST THING, VERY IMPORTANT
CHECK YOU OWNERS MANUAL!!! Do you have VATS/PATS/PATSII? etc. If your key a special key? Does it have the black plastic with a piece of metal? is it thicker than normal? These are all safety features...some are easy to bypass (black with metal is a resistor, and is about $0.50 to do) some are harder (if you have a chip, it'* harder) and require addons...some (may) be impossible....my other car starts with a plastic key w/ infared in the tip, and is impossible to put a remote start in. These are all "anti theft" features, and if you ignore these and put a remote start in, things can get ugly. If you need help with it, post your type, and i will try and help.
Acc1 (or Ignition1)
Acc2 (or Ignirion2)
Crank (or Starter)
You need a constant (always + on battery). That'* about the easiest one. Your best bet (as with anything that'* going to draw a decent amount of power) is to run a 10 or 12ga wire up to the battery (ALWAYS fuse within 12" of the + of battery). If not, you can tap off of the pack of wires running to your key (but by running your own wire, one less to "tap" into). I'll cover the other wires down below.
Now there'* at least 3 types of remote start.
RPM (or Tach)
Vacuum is least common. RPM taps onto your RPM wire, and uses that as a point of "car running". Voltage Sensing is as the name implies, voltage sensing. If you can, you really want to use RPM - but you will have ZERO problems using Voltage Sense. Only reason i say RPM is best is because most reputable alarms will shutdown the engine if they rev over 3k RPM while on remote start.
Alarm/Remote Start Brands:
If you have the money, you will not go wrong with a Viper/DEI. In saying that, they are also the most expensive. I have had success with other alarms, but if your concerned with anything going wrong, but a name brand. Make sure they have plenty of documentation. Read it fully. In NY, there is a "kill switch" REQUIRED on any remote start (turn to off, car will not start with anything but a key)...and i always suggest that you buy an alarm with them.
Now the down and dirty: Installation
-Are You installing a alarm/remote start?
-If you are doing an alarm and remote start, install the alarm FIRST. DON'T touch the remote start part yet - get you alarm working to your liking, then tackle the remote start.
-Do you have at least a day of no usage for your car?
-If your installing for the first time, plan on it taking you a long time. It'* not that difficult, but you want to take your time and do it right
-Do you have the tools you will need?
-Here'* what i suggest as a MINIMUM:
Wire Strippers/Cutters, Knife, Zip Ties, Multi Meter, Electrical tape, Butt Crimps (or soldering iron/solder...but it'* a bit harder)
-I have a test light (ground clip, sharp + probe). Can i use that?
-Yes. BUT, i do not suggest it. Why? It actually carries electricity through it (as in it'* using it to light a bulb)...so whatever circuit you test will need to carry the capicity the bulb requires. For some places, this may be fine. But what happens if you accidentally hit the (Well marked) airbag wires? BAM....there they go. With a multimeter, it draws milliamps of current, and is highly unlikely to hurt your electronics. I highly suggest a multimeter, and for $20, home depot or Radio Shack has decent ones (which also check resistance, diodes, amps, ac/dc, etc)
OK. So you car is parked. You have a multimeter. You have your keys. Your car runs. Your ready to go. Drop down that panel underneath your driver side. Look for the big bundle of wires going up the steering column. Find a suitable place where you are going to "Tap" into all these wires. Make sure that once your done, it all will tuck nicely back under there, and it will not disrupt anything else.
You have the bundle, and the location....how what? If the wires are bound together with tape or anything else, carefully remove the tape and clean them up. Seperate them out (so you can do testing on them) and WRITE DOWN ALL THE COLORS NOW!
This will help greatly.
Take out your multimeter. Set it to DC Voltage, or DC Voltage 20V. Take the black, your ground, and find a nice ground location. An alligator clip is helpfull, as it will hold the lead to ground this whole time. With the key out of the ignition, probe each wire carefully until you find +12V. Write this down on that piece of paper. Next, turn the car to ACC. Probe all the wires again. You allready have the Constant 12....now there will be 1 or 2 wires which show voltage. Mark those down "acc". Next, turn the key to "on". Measure wires. They should be similar to acc, with possibly another +12V. This would be your Acc3. The next step is tricky, and may take a long time. You need to find the crank wire. If you only have a couple of wires, then this may be easy. Pick a wire. Probe it. Hold the probe there. While turning the key to crank position, look for +12V on the multimeter. The crank should be +12V while starting, and 0 while running. Mark this wire down.
You now have a piece of paper with all the wiring colors on it for your car. Copy it. Put it with the owners manual, or somewhere with your documentation.
Now you have some options. If you have an alarm...do you want a starter kill? Do you want your heat to come on with the start? etc.
Now'* the time to lookup the wiring from the remote start manual.
On paper, match up all the wiring colors. If you have a Acc3, most alarms require a relay for that.
The first wire you want to connect is you Constant +. As i suggested, best bet is a + from battery. If not...tap into the + on the bundle.
How do i tap into the wire?
several ways...as people suggested, you can strip the wire (be very carefull) and "wrap" the wire around, then tape it over. You can use butt connectors (yellow). Or, you can solder. Soldering is the most professional and clean method, but if you haven't soldered before, this isn't the place to learn. My preference is butt connectors over stripping and wrapping, but thats all up to you.
Now that you have a positive, Pick the first ACC wire. Tap in. If you want heat and all the functions as if the key were in, also connect acc2. If you don't, your going to need to see which (Acc1 or Acc2) controls heat, and not attach it (but verify the car will still start).
Now do you want a starter kill? This scares people, as they believe that if the alarm malfunctions of breaks they will not be able to start the car. Not true, if done properly. To explain why, i will need to explain about relays quick.
Relays have 5 "posts" 85, 86, 30, 86, 87, and 87a. What does this mean? 85 + 86 are the "coil", which you can think of a light switch. Polarity (+/-) does not matter on this, as long as one is + and one -. The relay will work on about 9 - 18vdc. 30 is "Common". 87a is NC and 87 is NO. NC...NO? Normally closed, Normally open. This may help
When you apply voltage to 85 + 86, the / switches, to make 30 + 87 connected.
Instead of re-inventing the wheel, this is a great site for all your 12v needs, and will explain starter kills:
If you don't want a starter kill, then just tap into the crank wire. If you'r using Tach sense, find that wire and tap in. If not, your done.
Now'* the time to set various options on the Remote Start (crank time, run time, Tach or Voltage sense, etc). Once your satisfied with that, try the remote start. Adjust Your options, and if it works...congratulations!
-Car starts then runs for a minute or two, then turns off. "Security" light may come on.
-You didn't check your manual, did you? You have some anti theft system, and didn't bypass correctly.
-Car cranks too long
-Lower crank time, or try the Tach Sense.
-Car does not start.
-When you hit remote start...what happens? does your radio and other things get power? does it try? post more details
-Some things (heater, radio, wipers) etc don't come on
-You missed a Acc (ignition) wire....
any other questions or comments...post em'! I've done hundreds of remote starts, and seen it all and done it all.....this is far from "Everything you will encounter", and may contain mistakes. Hope it helps though! I'll be installing an alarm and remote start in my 92 bonne sometime soon, and i will take pics of every step and post them for you all.