what kind of relays do i need?

Go to Radio Shack and purchase an 1/8 inch to RCA adapter, connect it to the output of the secondary radio and to the input of the primary unit.  When you want to use the secondary deck simply select aux in on the primary deck and power up and play the secondary unit.

There will be minimal extra current draw from the secondary unit.  Maybe 2 amps of current.  The main current consumption of a radio is the current needed to drive speakers.  The secondary unit will have no speakers connected to it, hence the couple amps of current.

i am an idiot wrote: Go to Radio Shack and purchase an 1/8 inch to RCA adapter, connect it to the output of the secondary radio and to the input of the primary unit.  When you want to use the secondary deck simply select aux in on the primary deck and power up and play the secondary unit. There will be minimal extra current draw from the secondary unit.  Maybe 2 amps of current.  The main current consumption of a radio is the current needed to drive speakers.  The secondary unit will have no speakers connected to it, hence the couple amps of current.

okay i see what you mean and how it would help save power but id like to have two fully functional head units, not to have on piggy back off the other. the more i think about im liking the idea of keeping both powered, but flipping a switch to change the outputs between the two. but if my car cant handle that kinda demand im perfectly content to have one work at a time. im sorry, i know its easier but not really what i was looking for but thanks for your interest in my topic:)

OK, I stand chastened, you shouldn't need a switch for the following reason You will need one standard automotive and two 4PDT relays such as Mouser part #655-PT52AO12B One radio, your second, is the default, left switched on all the time, as soon as you turn on the original that will come on and turn off the aftermarket, turn it off, back comes the aftermarket The reason is that you will use the factory amp out (remote switch lead) to also trigger your relays Thus turning on the original radio will switch the speakers and the power to that unit Here's how- Normal Bosch style cube relay, ACC from ignition switch to 30 ACC to new radio 87a ACC to old radio 87 Ground to 85 Join to your amp switch lead from original radio via an inline diode 1N4004 to 86 band, (cathode) and to the amp again towards the amp Another of the same diode across 86 and 85 with the band (cathode) to 86 Now here's the complicated part, link 86 to both of the four pole relays, ground the other side of both coils 4 speaker plus outputs to 30 From original head unit to 87 New head unit to 87a Repeat with last relay for speaker minus outputs 85 = coil minus 86 = coil plus 87a = N/Closed 87 = N/Open 30 = Common Having said all that you will also need shrink sleeving to go over the terminals on the 4PDT relays as insulation the soldering part on those relays will blow your mind it's so boring, the constant 12v+, illumination, grounds etc can also be joined to both, RCA/phono leads also the amp switching lead on the second radio should also have an inline diode as above. Having done all of this you do realise that Mr. Idiot's last post was a much better idea, assuming you can reach both units

okay. you win haha you lost me. i still dont understand how i would manually switch between each radio. and whats with the diodes? also i know that idiots way is super easy but its not what i want and it would double eq the second radio and my second radio is out of reach. why wont my original set up work? just having relays and one radio is on in the "off" position and the second is on in the "on" position(possibly keeping the remote and acc,constant,ground,illum all hard wired to each radio if it wont use too much power just to have a second powered) i know im being difficult/newbie, but thanks for everyones help so far:) im really liking the12volt community

Which is why I made that comment, actually that pompous crap about "undisclosed" location really got to me When your dealing with people like Mr I and myself who install stealthed tracking equipment for a living undisclosed doesn't mean much. Again with the second head unit on all the time via the ACC, you won't need a switch, the diodes are to protect the output stages of both head units from feedback when the other is on Your last suggestion will work fine if you're not powering up any speakers, just line outputs to amps. Otherwise do as you suggested and wait for the feedback to blow up your head units, hence isolating or switching relays.

Howard!! It was undisclosed reasons - not location. If you & Mr I are having troubles tapping into echelon let me know and I'll branch my pipe - that's assuming yous lack the quality I enjoy. (Don't worry - it's still the same virtual wave technology... and still undetected. Don'tcha love fibre-optic technology?!) And don't give LocDet info... PS - I should send you that joke about bouncing proxies... it's so last millennium (probably not even 8-bits at that!).

Peter Echelon ONLY listens to the US from here, NSA listens to the UK you listen to NZ (boring), NZ listens to you and the Mossad does the rest of the world

Geez they really don't trust you do they? I could say it's all Greek to me... but that was local (Simpson) which is may not have been linked in... (NZ don't have Greeks do they? I think NZ got the Scots et al, we got the Poms and the South of Romers. Meanwhile we still track semi-trailers to our north... maybe even London....

I've done tracker installs where they wanted two in a vehicle but I recently did some work where they wanted three because the drivers were so untrustworthy.

Crikey - three >20kW amplifiers in one vehicle! We prefer to keep ours remote and fixed - mobile stratosphere modeling is just too far over most peoples horizons... er, I mean... heads.