Gs300 Bypass Harness With Faulty Amp

nightrave · January 10, 2016

Hi Guys,

After giving up trying to fix my sound (sound went dead after battery poles mixup) I am trying to figure it out how to solve it. I have read a lot about installing a new aftermarket head unit. The easiest way is to bypass the amp like they show in this tuturial . The problem is I can't get it :( What to wire where. I have found a ready harness here so I have 2 questions.

1. Do I just unplug two connectors from the amp, put in the two connectors from the harness and connect the other end to the new aftermarket unit?

2. Would this still work if my stock amp is dead?

sorry for stupid questions, I am really confused and irritated for not having music in my car for almost 6 months :(

BRZ · February 2, 2016

I guess this would depend on weather the Battery pole mix up has blown the amp supply fuse, as I understand it this powers both amp and radio!

Carcathan · February 3, 2016

HI, i'm just in the process of bypassing my 2002 GS430 OE stereo set up, switching to a replacement Kenwood headunit.

Assuming that the people selling the bypass cable have got their wiring right then yes, this is essentially plug and play - of the connectors that plug into the existing amp, there are only two that will fit the two white connectors shown on the bypass cable - so you really can't go wrong once you've disconnected the plugs from the amp.

Once the amp is disconnected then it won't work - i just removed mine. That also means any related items (like the Rear Sub and SatNav if you have it) probably won't work either (or atleast i couldn't see how to keep them working). So in my case i've removed the Amp, CD disc changer, Radio and SatNav unit - all because the radio was no longer working and it simply wasn't cost effective to replace. I'm using the headunits own internal amp for the speakers as it's a decent Kenwood model and i'll be replacing the rear Sub (no longer connected) with a replacement Sub (and Amp i think) powered via the Kenwood headunit (how that works depends on the headunit you choose and will be a different set of wires if done properly).

The ISO connectors on the bypass cable will work with most stereos - so again that should be plug and play.

The only two connectors that probably aren't catered for are the Dimmer/Dash Lights' connection and the Aerial Power connection. On the OE SatNav version that i have i just identified the two wires at the back of the current radio that provide those and made those connections there. In my case there were 3 wires to the aerial - i found that powering the black/white aerial wire operated the aerial so i've left the other two disconnected. I think the Dimmer/Lights was a light green wire - easily found with a multimeter by turning the lights on and off. But you need to check the wiring diagrams for your existing set up and your new stereo. But neitehr of those will stop you playing a CD/USB/Aux in connection on the new headunit to test that the basic system is working.

At least on mine everything is working on the new stereo - it's just the other spin off work that's taking the time as i'm changing the location of the replacement AC controls to a non-standard location (as my AC was originally controlled via the SatNav screen), i've made a small one-off fascia for my stereo (sucker for punishment!) and i'm just working out how to mount a Nexus 7" tablet in a way that suits me. None of which is probably relevant to you - sorry!

But really nothing to stop you now you have found that bypass cable - assuming you haven't blown some other fuses, but that's a different issue.

CustomIce · February 10, 2016

On 1/10/2016 at 6:44 PM, nightrave said:

Hi Guys,

After giving up trying to fix my sound (sound went dead after battery poles mixup) I am trying to figure it out how to solve it. I have read a lot about installing a new aftermarket head unit. The easiest way is to bypass the amp like they show in this tuturial . The problem is I can't get it :( What to wire where. I have found a ready harness here so I have 2 questions.

1. Do I just unplug two connectors from the amp, put in the two connectors from the harness and connect the other end to the new aftermarket unit?

2. Would this still work if my stock amp is dead?

sorry for stupid questions, I am really confused and irritated for not having music in my car for almost 6 months :(

I'd be doing the same thing as BRZ has suggested and replacing fuses.

You will have reversed the polarity for the entire vehicle when mixing up the Battery poles, but that doesn't always mean you fried anything. I'd be looking at fuses in the fuse boxes, and on the units in question.

You might not have a problem at all in reality.

nightrave · February 10, 2016

On 2/3/2016 at 2:45 PM, Carcathan said:

HI, i'm just in the process of bypassing my 2002 GS430 OE stereo set up, switching to a replacement Kenwood headunit.

The ISO connectors on the bypass cable will work with most stereos - so again that should be plug and play.

3

Was your stereo working straight away? I had no power on it when I connected the harness. I had to cut the wires from the plug that used to be connected to the old head unit and attached the grey to red and blue(with yellow stripe) to the yellow wires of the ISO harness. Now the radio does power on but goes directly into protect mode. According to the manual it means that the speaker wires are short circued or touching the car. No idea what to do anymore. I have read that you need to ground the unit, which I have not done yet, but not sure if that's the issue. Any suggestions are greatly appreciated.

Carcathan · February 10, 2016

I did look at connecting to power and earth directly behind the radio but when i looked at the wiring diagram the power and earth to the amp were actually better (thicker wire) and aligned with the pins on the amp end of the patch cable.

That sounds like one of your blown fuses may be affecting the power to what was the amp - i'm sure one of the audio fuses only supplies the amp.

The colour coding for the speaker wires is pretty easy to work out with the audio wiring diagrams that you can find here through search - so it would be worth you methodically checking both sides of the plugs at the amp end to make sure those are correct. As i'm of an age where i need glasses more and more i actually took digital photos on the plugs from several angles and then put them on the pc so i could zoom in, see the colours clearly and check them against the wiring diagram.

These are the two diagrams i used (i think Tigerfish posted them on here - mine is a 2002 so these applied to me perfectly) they may not be right for your model so check the colours. But they don't show which wires go to which connetor plugs - so i recommend taking photos. Try disconnecting the speakers then bridging one pair at a time with some spare wire - that might help establish which speaker is the problematic one.

But certainly sounds like you have some kind of fuse issue, which i see the others have been advising you on better than i can.

nightrave · February 10, 2016

Thank you for replying! Will check the cables one by one tomorrow morning! It is definitely not a fuse issue as I have checked them all with multimeter - all fuses are good (there were blown ones but I have exchanged them already)

nightrave · February 11, 2016

ok. Now it's me just being me. I have pulled out all the wires from the iso harness (which I probably shouldn't do) and rearranged them according to the schema. Now nothing works at all. The radio doesn't even power on. I am clueless. I have tried taking the power from the amp connector - nothing. Trying to get the power from behind the head unit - nothing. I mean technically, in order for the stereo to power on, shouldn't those two wires connected be enough ( RED ACC and the YELLOW 12V)? Can't understand what I am missing to power it on.

Carcathan · February 11, 2016

OK, removing the wires from the ISO harness is not the worst thing so long as you are going to be methodical before putting each one back!

Do you have a multimeter or a test lamp so you can establish for certain that you have power from the car 12v supplies? One is switched and one is permanent - so establish which is which and that they do provide power and then check which colour that is meant to be supplying at the stereo end (sometimes red and yellow have to be switched around).

But it still won't work without the power being earthed - so check that it is the correct earth wire and then do the same check for the stereo earth wire.

Once you have those three connected then you should be able to see the stereo power up and hold a settings in its memory - if not then the either the connection plugs aren't making a good connection or the stereo has blown it's own fuse (10 amp on the back?). So again use the mutimeter on the stereo end of the wiring to make sure the supply is definitely reaching the stereo and being earthed.

Then use the same process for the speakers - start at the stereo end, make sure you know which two wires are for an individual speaker then follow that through to the car end and connect those two up - turn it on and use the fader/balance controls on the stereo to isolate that speaker and make sure it's the correct one. Then do that for the remaining speakers. Don't guess or assume on any wire colour as car wiring is always more confusing than you think.

Lastly, if you're really struggling with these principles consider whether you are the right person to be doing wiring!! It isn't everyone's skill area - some are better at mechanical/bodywork but won't touch wiring, so it's no shame to admit defeat and get a mate in who's got more skills in this area.

nightrave · February 11, 2016

Thank you so much! You are extremely helpful! I do have a multimeter so will go and check the wires. The only bit that I am struggling to understand - which of the wires of the harness, that initially was in the amp, is the ground one. Or do I just take the ground wire from the ISO harness and attach it to car body?

TigerFish · February 11, 2016

The white and black wire should be ground, but you can just connect to the car body instead (that is all the harness wire will be doing a short distance away).

Sent from my Iphone using Lexus OC

nightrave · February 11, 2016

Holly molly! It's alive!!! After almost 7 months I've music in my car!! Thank you so much everyone! Two things I still trying to figure out to make the job perfect:

1. In order to connect the sub - do I need to lay down new wires from the sub to the new unit or do I just connect it parallel to one of the speakers (not ideal but...)?

2. How to make the antenna pull out when I switch to radio? Currently it's just retracted.

200h · February 11, 2016

you've answered your 1st question yourself run a new set of cables,if you have preout on the back of the stereo run these cable to a new amp then hook up your sub

on your wiring loom there should be an accessory cable connect this to your aerial power cable.

nightrave · February 12, 2016

16 hours ago, 200h said:

you've answered your 1st question yourself run a new set of cables,if you have preout on the back of the stereo run these cable to a new amp then hook up your sub

Thanks! Technically - the stock amp was powering the sub before, right? So would I be wrong to assume, that some of the wires that were going into the amp lead to the sub? I know I am probably wrong, but that does sound plausible :)

Carcathan · February 12, 2016

the trouble is that the wiring from the amp to the sub is essentially speaker wire so far as i can see - and the sub is spec'd to suit the slightly unusual Lexus amp.

So in principle the best solution is to replace the sub with a more standard free air model, use your head unit to power a separate amp in the boot (hence the need to wire it up the way 200h suggests) and then connect that new amp to the sub.

I have read on another GS forum that it might be worth connecting the new headunit direct to the amp speaker wires as you suggest. Some people have spurred off the rear speaker wires - but that sounds like it can be fairly poor sub output and possibly damage the sub/headunit long term - not sure of the technical reasons.
As my headunit has a pre-out specifically for a sub i'm going to try and connect that direct to the sub speaker wire near the old amp - there is a report on the other GS forum that it worked, and as the lead is a couple of quid i'm going to try it before going to the trouble of a new sub, amp and wiring the length of the car. No idea if it will work or work well. Should know in a week or two - unless you find a solution sooner!

200h · February 12, 2016

1 hour ago, nightrave said:

Thanks! Technically - the stock amp was powering the sub before, right? So would I be wrong to assume, that some of the wires that were going into the amp lead to the sub? I know I am probably wrong, but that does sound plausible :)

have a look at the sub wires and make a note of the colours so you will know what wires you are looking for

at the amp end of the cabling,once the cable are located if you are unsure which wire is + and which is - connect a AA Battery across the 2 wires

you will hear a pop sound this is because the speaker cone has moved when the speaker has moved outwards

you know what wire is + & - from the connection on the Battery