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Topic # 57741 23-Feb-2010 13:07
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I bought a car stereo, and I've been trying to get the thing to show any signs of life. One of the previous owners has butchered the wiring, so I decided to give wiring it up a try. I've checked google for wiring diagrams and so forth, and as far as i can tell...i have the car wiring attached to the ISO connector in the correct way. Only problem is, the head unit doesn't power up.
Either the wirings wrong or the head unit is a dud. Any suggestions on how i might go about testing both scenarios? I have a multimeter around here somewhere, what leads should I be testing?


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  Reply # 301461 23-Feb-2010 13:11
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More info on the actual unit you are trying to install and make/model of the car may help.

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  Reply # 301462 23-Feb-2010 13:14
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1990 Toyota MR2, Domain Head Unit DM-B528MP. The head unit wiring ends in a standard ISO connector.


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  Reply # 301584 23-Feb-2010 17:04
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Fastest way to check is get another head-end and plug in. There are so many connections - even for 12v, 12v stand-by, 12 v accessory, it can lead to a crazy head case situation. You mentioned butchered wiring - is that on the ISO wiring or the head unit ? Either way, it will end in tears. Lots of tears.... and blown fuses, smoked wiring looms, and carcked speakers.
You may even be able to take the head end into a car stereo installer place and get them to test it - maybe for a small fee. Probably would be the fastest way.

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  Reply # 301600 23-Feb-2010 17:59
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standard iso wiring= yellow fulltime, red accessories, black earth ( negative )
inplug the iso wire get a multi meter or test light, if neither available use a 12v bulb connected to wire, test each of the car looms wires seperatley, earth to a metal part of the dash or somewhere you know it is earthed. It could be the fuse has popped on the fulltime (positive) wire

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  Reply # 301624 23-Feb-2010 19:32
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I always find this site handy:

It has most vehicles listed with wiring diagrams etc.

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  Reply # 301635 23-Feb-2010 19:59
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Ah yes. The MR2. They're fun.

Now, from memory, the colouring of the wires is standard across the board for Toyota's of that era.
If you can find a diagram for that, and match it against your new headunits diagram, you should be sweet.

Btw, the MR2 has a factory 8inch sub, for which is has its own amp which is located in the side panel on the passangers side. The amp from memory is a bit funny with headunits. I think it only works with the factory one.
Luckily, because the cabin is quite small, a couple of 6x9's will give a good bass sound.

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  Reply # 301641 23-Feb-2010 20:10
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easiest way i found to test the headunit.

wind/tie/knot the 12v constant and 12v acc wire together on the headunit wireing harness, find a suitable earth, and touch the two wires to all the wires coming out of your car for your headunit.

repeat once with ignition off (to find constant)
and again with the ignition on (to find acc power)

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  Reply # 301644 23-Feb-2010 20:25
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Cheers everyone for all the advice, after some fiddling I managed to get power to the head unit. The wire for the ignition switching doesn't appear to work, so for now I've tied both into the battery line. This means i have to manually turn the stereo on and off, but its working. I've been tying all the car's wiring into a pair of standard ISO plugs, so hopefully no current or future owner of the car will have to do this again.

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  Reply # 301678 23-Feb-2010 22:03
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rassnor: Cheers everyone for all the advice, after some fiddling I managed to get power to the head unit. The wire for the ignition switching doesn't appear to work,

Blown Fuse, test light or multi meter your fuse box

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  Reply # 301929 24-Feb-2010 22:14
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Does the clock work? If not blown dome fuse. As Adam said, some of the MR2's had an active audio system, all speakers were amped, amps are behind the panel under the passengers seat belt. It was a 4in sub from memory. I rewired mine from the ground up when I had it, put in some decent 12gw direct to the battery and a decent fat earth.

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