Thread: ignition wire

Originally Posted by TeamRSX

Since i will have amp, dsatx and hd radio on ignition on harness for trigger. Will there be too much strain on the ignition and am better off using a relay?

Originally Posted by DarquePervert

No, you're not putting too much sctrain.
All three of those devices are only using the ignition line as a trigger. They are drawing a negligable amount of current.

Ok, i have heard a lot of ppl saying if your going to have more than 2 devices as a trigger on your ignitnon line that you should just use a relay to turn on the devices.

I am also going to be adding another amp to my system, so i will eventually be using 2 amps, dsatx and hd radio for my ignition trigger. I know they are not drawing a lot of current, but would i be safer to add a relay or really makes no difference as the amount of current will never exceed the 7.5a fuse i have for my igntion wire?

I ran 3000 watts of amp, lighting, ect..all on one ignition wire.

You do not need a relay.

A relay is really only to turn things on at slightly different times to avoid a thump noise when your turn on your car.

You do not really draw power from your ignition wire.

Think of your ignition wire as a switch. It is either on or off. It can never be "too on" lol.

Originally Posted by FusionFanatic

no, that is NOT what a relay is for... and no, that is NOT what a relay does...

a relay is used to control an electrical device(s) from a separate/isolated electrical source. it's usually used to control a higher power circuit with a low power source.

in an electromagnetic automotive relay; it only takes a split-second to energize the relay coil. once power is applied to the coil, the relay is switched almost instantaneously (not enough of a delay to prevent a turn-on-thump).

with a remotely turned on device like a car amplifier; the main power is drawn from the 12v+ constant wire, but some power is still drawn from the ACC/IGN wire. it may only be a small amount per device, but it adds up when hooking up multiple devices.

the car's ACC and IGN circuits are not general power wires. they are there to power factory installed components. when you hook up additional devices to them, you are drawing more power than the car manufacturer designed the circuit to handle. for this reason it is a good idea to use a relay to keep the additional power draw to a minimum.


just because you did it and your car didn't catch on fire, is not a good reason to tell others that they can (or should) do the same thing. each car is different; wire sizes, wire lengths, factory power draw, fuse rating, etc all vary from car to car. what works ok on your car may not work and may not be safe on another. using a relay to minimize additional power draw on the car's ACC and/or IGN circuits is a good safety measure to protect the car's factory wiring and should not be discouraged.

Ok, thanks for the info. I'v had several ppl tell me a relay is a good safety measure. My stock igniton wire on my harness is protected my a 7.5a fuse.

I currenly have my amp, dsatx and hd radio getting the trigger from the igntion. Seems to work just fine, but was really thinking of putting in a relay for those devices especially since i want to put another amp in.

Seems that ppl who have relays suggest to put them in and ppl without them dont recommend them.

From what i have read and from what some ppl have mentioned its never a bad idea to isolate your wiring from the stock wiring.

The only think i was not sure of is how big of a power wire i need for the relay and what size of fuse to use on that power line. Since i will only be using the ignition wire as a trigger how big of a power wire is reccommended?

I was planning on getting a 30a relay, but not sure how big of a wire and fuse to use. I guess i could keep them small as not much current is used to trigger the devices.

Originally Posted by FusionFanatic

yes, you should always isolate your own wiring as much as possible from the car's factory wiring. the only non-factory electrical device that is directly connected to my car's factory wiring is a single 30A automotive relay triggered by the ACC circuit that was formerly used to trigger head unit. everything else is powered or triggered from the relay.


if you're absolutely sure that you won't be directly powering any future devices from it then you can use a small wire with a small fuse. if you think you may want to add devices later on (for example; hardwire a cellphone charger, radar detector, etc) then you may want to use a larger wire with a larger main fuse.

I run a 10awg wire with a 10A fuse as my power wire because I use it for more than just remote triggering. I use my relay to directly power my PAC SWI-X, radar detector, and a center console power jack (for cellphone charger, etc); as well as a signal/ trigger for my M2-ATX, equalizer, and 2 amplifiers. I run another 10awg wire with a 15A fuse to provide constant 12v+ to my M2-ATX and equalizer. I run a 4awg wire with a 40A fuse for my amplifiers.

as you can see I'm a little overly cautious when it comes to car wiring. I learned the hard way 10 years ago (I was 17 then ) when my first car caught on fire and burnt to a crisp due to my insufficient amplifier power wiring. I'll never make that mistake again

...the point is. you can never be too safe when it comes to car wiring. wires CAN and WILL burn up if you put too much of a load on them. if you're ever in doubt of how big wire gauge you need, ALWAYS GO BIGGER! (and use the smallest fuse possible regardless of wire gauge)

Wow. looks like your wires are protected.

I will only be using the relay for my remote turn on for all 3 devices. I will not be using it to power constant 12+ to any of the devices, but rather just using it as a trigger to turn on the devices.

I will be using the relay for remote turn on for 2 amps, dsatx and hd radio. Since the current draw is very minimal i was thinking of originally using 10awg from the battery to the relay. Maybe i could go with smaller wire like 12/14awg? Then for the fuse i was going to use something small like a 7.5 or 10a fuse.

I was just determing what style fuse to use if i went with 10awg wire. I think the smallest awg style fuse i have seen around is 20a and i will need something smaller. I guess i could just go for a regular inline fuse, but from my understanding they usually come with small guage wire like 14/16awg.