when are relays needed for accessories?

I have downloaded and read numerous install manuals for car alarms and remote starts. I'm somewhat confused to know if I need to utilize a relay for parking lights, dome lights, trunk release, etc. Some manuals reference onboard relays for these devises so am I to assume I wouldn't need a relay for that wire?? Just connect the output to the light or trunk release?? Some say very little but tag the output wire saying it has somewhere between 200-500 ma of current. Will that amount of current drive those accessories or would a relay be needed?? Some are very vague about the output for those items and of course I can't find a manual for most Autopage systems, so I don't know about them. The Bulldog manuals are quite specific about the need for relays, but I haven't seen where most here recommend that brand. Is it safe to first hook up the output wire to see if it will drive the accessory or is that not wise?? By the way whatever I decide on will be going into a 2006 Ford Taurus. Thanks for any input!!

In General: If the car's wire is a high-current circuit, and you hook up your alarm's low-current output directly to it, you'll probably burn out the output from the alarm. (You might get lucky if you try it just once or twice.) Yes, generally speaking, if the unit has an onboard relay, you would just connect directly from your product, to the wire on the car. (For example, most alarms/starters have an onboard parking light output, and can drive a car's parking lights directly.) Generally speaking (although not always) if a car's parking light or trunk wire is a negative trigger, it's probably low-current and you could connect your alarm directly to it. On the other hand, if it's a postive, it's probably high-current, and would need a relay (whether internal to your product, or you wire it externally). Most of us professional installers are not impressed by Bulldog's limited range, and lack of extra inputs/outputs.......but since they're made for the do-it-yourselfer, they do have great, well-explained wiring information on their site and with their products. About your Ford Taurus: The pink / YELLOW and pink/green lock/unlock wires at the bottom of the fusebox are low-current, and don't need a relay. (If you plan on configuring the optional driver's-priority unlocking, that would need a relay, though.) If your trunk-release wire (at back of switch) is negative, it's low-current, with no relay needed. If it's postive, it's high-current, relay required. (They seemed to have built these cars both ways, so you have to test.) The brown parking light wire (near fuse box, or back of headlight switch) is positive, high current. But most products have a parking light relay already on-board. If your alarm has a domelight supervision output, there's a low-current (light GREEN/ orange) wire at the back of the dimmer switch. You can connect directly here, no relay needed.

Chris, Wow thanks so much for the information!! Gives me a heads up now when choosing my alarm or starter and what to expect for hook-ups. I assume, I know that's bad, that the horn output on the alarm would work the same?? My Taurus has a negative (Dark Blue) wire so that should also be low current and would probably not require a relay?? And yes I believe my domelight supervision is positive (BLACK/ Light Blue), but if I can find the wire you mentioned I would be OK?? Again all depends on what kind of onboard relays the system has, seen some with 4 or 5 and a few not many.

The horn wire is low-current, yes. The blue/black domelight wire listed on the tech sheet is on the high-current side, and if you choose to connect there, you would require a relay, yes.   The blue/black is the wire that exits the body-control module, and goes right to the bulb(s) in the car. The light/green orange goes from the switch, to the body control module, and activates an internal relay inside there. (You can hear it click inside the fuse box if you move the dimmer wheel all the way to the top position.) Just did alarm/starter in my girlfriend's 2000 Taurus, and use the light GREEN/ orange with no relay, with no problems.

I tries this on my 2000 Taurus, Viper 571 domelight supervision (H1/4) to the light GREEN/ orange wire at the back of the light switch and it works like a charm.  No relay needed just like Chris said.