I had a shop install my Nakamichi MB75 in my old car (98 vette) and I'm moving it to a 99 vette. I figured this should be idiot proof. Funny, make something idiot proof and they make a better idiot.

I put a new GM wiring harness on it, because I kind of screwed up old one installing it.

I have the red, black and yellow wires connected and the unit powers up enough for me to eject my CDs that were in it. The problem is the display won't turn on. I took it into a shop and they hooked it up on the bench and it worked fine.

I didn't have an amp or any speakers connected. Also there are two orange wires (illumination) on the GM harness and I don't know where to connect them.

Thanks for any help you can provide.

 

The C5 stereo does not use the standard pinout that is in most older GM cars. Most installers have no clue on the wiring of the C5. The HU is connected to the car DLC serial data buss. It gets various control messages sent to it from the BCM and PCM like power ON/OFF, illumination changes, car speed changes ...etc..

You DO NOT want to connect to wires in the HU harness you are unsure of. Only use the 8 speaker connections, unswitched power and ground. Other connections are not to be used.

1. The HU does not get a switched power input from the car. The BCM commands it on. The HU then outputs switched power to turn on the stereo modules. You must find a switched power point to tap and add a power relay for a high power deck.

2. Unfortunately you will have to tie your illumination input to +12 and leave it fixed. The HU is not connected to the car dash illumination. The BCM commands the HU for illumination changes. The dash illumination is driven by the BCM which uses a technique called PWM to vary brightness. The bulbs are connected to +12 volts and then the BCM "pulses" them to ground.

Signal CD/Radio connection

Power C1(10) ORG
ground C1(5) BLK/WHT

RF+ C1(4) DK GRN
RF- C1(3) LT GRN

LF+ C1(2) TAN
LF- C1(1) GRY

RR+ C2(18) DK BLU
RR- C2(17) LT BLU

LR+ C2(20) BRN
LR- C2(19) YEL

 

What 99HT said...

Actually, in layman's terms ...

The connector will get you what you're wanting for a full time power source, but what you're missing is your switched power source. If you look at the pin on the connector you've got hooked up to your new headunit that is for switched power, then look at the factory harness that you're plugging into, you'll notice that the factory harness actually has nothing at that pin slot. The reason (as 99HT already stated) is because the Corvette uses the Body Control Module (BCM) to turn on the factory headunit. Well, you can't use the BCM to turn on the aftermarket Nakamichi (or any other brand) unit. You need a switched power source. I went over to the ignition switch for mine. You may find a better place though?

 

99HT, I'm sending you a diagram of how I'm thinking of wiring this. Could you let me know if it looks ok?

I would put it online, but my webserver is giving me problems right now.

 

Superficially it seems OK. You must be sure not to cause a ground loop between the modules and that the power you are pulling out of the footwell to feed the power amp will not be too much for the harness to handle.

A simple schematic is only going to give me a rough idea what you are going to do.

 

Got the AC controls moved to where the ash tray was, last night. Turned out pretty good. I cut a horizontal slit on the bracket on the right hand side of it so it would slide over where the dash mounts to the metal frame. Really, really snug. Dremel tools rock!

Tonight I'm going to build a little circuit board with a voltage regulator and some capacitors for power to the computer, then the stereo install!

 

"Tonight I'm going to build a little circuit board with a voltage regulator and some capacitors for power to the computer, then the stereo install! "


Do you have any idea how much the "Computer" draws for current? Be sure not to overheat the regulator.

 

Computer uses 18V 3A, it'll run fine at 12V, some I'm guessing about 4.5A at 12V. I'm trying to find someone locally who sells voltage regulators that'll handle that amount of current.

 

Also, where should I get the switched power from? I have my Valentine 1 wired into the accessory plug in the passenger footwell, should I just connect the HU there also?

 

I assume you are talking about a laptop computer? You must test your laptop to see if it will run AND charge the battery on +13.8 volts. You may need to buy a special adapter from the laptop manufacturer that convert +13.8 volts to the correct voltage.

You will not need a to build a voltage regulator to convert 12 volts to 12 volts.

 

The reason I was going to use a voltage regulator is because the voltage is kind of dirty and jumps between 12.8 and 14 in a car.

The computer isn't technically a laptop, but it's about the same size. I actually found something that converts ~12V to ~16-21V, should work perfect for the computer.

Here is a link to the PC. http://www.armcomputer.com/armg1/home.htm