Can't Find Ignition Wire!

[justind89]

Ok, so i'm trying to run wiring for my new head unit, but with a continuity checker (just one of those screwdriver lightbulb type things) it definetely works as when i touch the positive terminal it lights up, but when i try to check it against every single pin on the radio plugs none of them will light up with the ignition on or off. i don't see how this is possible as i'm sure the stock radio needs power since even lexus doesn't have radios that run off dreams and magic :)

[1990LS400]

even lexus doesn't have radios that run off dreams and magic :)

I see that you are in Australia where your Lexus radios do not run on dreams and magic like they do in here in the U.S. ;)

Maybe it is because we are "two peoples separated by a common language" but I don't understand why you are using a "continuity checker" to find the "hot" wire on the car's original radio harness. My continuity tester has a battery and two probes for sending a current through a circuit and sensing the current appearing somewhere else on the circuit.

I would think you would instead want to use an unpowered (no battery) 12 volt test light to sense which pin on the car's radio harness is the switched (hot only when the ignition key is accessory or run position) pin and which pin is the unswitched pin (hot all the time). I installed a bunch of aftermarket radios in Mercedes, Volvo, Honda and VW cars back in the 70's and 80's and using a 12 volt test light to find the hot wires always did the trick.

Some of the nicer multifunction battery powered testing devices can be used for testing both continuity and voltage ... and lots of other functions. I've got a really nice multi-tester but hardly ever use it ... I mainly use my cheapo continuity tester and my cheapo 12V test light.

[justind89]

sorry for being unclear, im a little tired as its past 2am here, but i meant a 12v test light. i can't find however the continuous power line straight to the battery or the ignition wire.

[1990LS400]

sorry for being unclear, im a little tired as its past 2am here, but i meant a 12v test light. i can't find however the continuous power line straight to the battery or the ignition wire.

Have you tried finding a "continuous power" wire or pin on a connector that plugged into the OEM radio or to the amplifier if your aussie ES has a separate amplifier? Back in the "olden days", I always found switched and unswitched power on a connector that plugged into the original radio -- I usually chopped off the connector from the car's audio system harness to wire the power wires to an aftermarket radio.

Sorry that I may not be following you. The aftermarket radios I installed back in the "dark ages" were usually pretty simple.

[justind89]

no, they really havent changed much since then, thats exactly what i was going to do, i'm just testing through the oem plug atm, but i might check the wires that hook up to the stock amplifier. either way the stock stereo should have a switched and unswitched power. but none of them are lighting up my test light! touching it on the battery confirms the light is working fine. going to check the amplifier plugs now

[justind89]

ok, so i've found switched and unswitched power on the amplifier harnesses (problem is they are under the passenger seat) i suppose i can run the wires back up to the head unit from . but its still perplexing that there are no power lines in to the stock radio. i'm jsut going to cut the plug off and figure it out :)