NONO5.0

Does anyone have a schematic of the ground distribution for an '86 Corvette? I can't find one anywhere

jackdaroofer

Most of the engine/ecm grounds end up on a tranny/bellhousing bolt in the upper corner on driver's side

Hope this helps

kickbackking

I have a schematic for a 85, not sure if that would be the same. Is there a particular circuit your looking for? Let me know if you want me to scan it or give you more information.

Later Denis

idcard

What are you in need of? I have 6 pages of ground info. in my manual. Page 8A-14-0 & 8A-14-1 is ground distribution (G201), 8A-14-2 ground distribution (G115,G116) front lights ground, 8A-14-3 ground distribution (G401) rear lights ground, 8A-14-4 ground distribution (G320) looks like brake controller ground, 8A-14-5 ground distribution (G104) looks like modules, switches, relays, ECM. Pictures that show wiring - show 1 ground wire on a stud forward of the fuel real on the drivers side, 2 wires on a stud at the rear valve cover on the driverside, 1 wire on the transmission bell - driver side. I don't have a scanner, but could copy and mail to you. Let me know if you need copies at my work cardnf@uwec.edu.

bballarin

Sorry to resurrect this old thread but I have the same need: ground distribution on an 86 for Bose radio/amps/antenna.

I have a scratching noise in the radio on the first 5 minutes after starting the engine on a cold car.
- noise seem to come from all 4 bose speakers
- noise level is independant of the radio volume level
- noise is present whatever I listen to: radio or tape.
- noise is still there if I start the engine with alternator disconnected
- noise is still there after replacing the ingnition noise filtering capacitor
- noise is still there after replacing the output/pre-amp board on my bose radio unit (with a spare one i have)
- noise is still there after reworking my 4 bose amps with all new electrolythic capacitors: audio grade, 105C, panasonic cap (significantly better sound by the way specially on treble)
- but noise is not there when engine turned off or after 5 minutes with engine running
- and sure enough, noise is not there with radio turned off

Any help appreciated.

What I am thinking next:
- test ground connections
- test resisitivity from radio/amps to battery and try to connect directly to battery.
- try If I still have noise with radio and amps powered on, but audio diconnected between radio and amps

Cheers,

BB

Cliff Harris

I don't know how the grounds in a Bose system are connected, but I have heard so much about ground problems that I scanned all the pics in the FSM that showed grounds and posted them on my web site. Click on a pic for a full size view:

http://home.earthlink.net/~cliff_har...s/grounds.html

I wonder if you could pull the fuse for the Bose and power it from an external battery somehow. That would isolate the power circuits. You mention disconnecting the alternator, so this might not help. I'm not familiar with how the speakers are powered. Each one has an amplifier in it, so they all need power somehow. My car has the non-Bose radio so I don't know much about them.

I do know that the fuel injectors pump some ugly noise into the wiring (high current & sharp power spikes are bad news, noise wise).

AGENT 86

Nice work on the grounds.
To the OP, Bose uses G125

pmihaltian

Well Done, Cliff. Thank you.

bballarin

Thank you very much Cliff!

Thanks also for the tip. Powering the audio amps with a distinct external source is an excellent idea to help isolate the problem. The 4 bose amps are powered from a single relay located next to the ECM under the dash on passenger side (can be accessed after removing the center console information cluster). That should not be too difficult to supply them from this location. The relay itself may be the problem too. I replaced it once many years ago even though the failure mode was different (completely ceased to function without advance notice).

Thanks again and this might help others too, here in France.

Cheers,

Bruno

bballarin

Hi Agent 86.

Thanks for the tip on G125.

Will let you know if I make any progress.

BB

bballarin

I have checked G125. There are 2 wires grounded there. One is obviously for the bose amps because it cuts the amps when I removed the ground screw. The ground contacts were of course not as bright as when they left the factory back in 1986 but not corroded. I have cleaned them up and screw them tight. As mentionned in your notes Cliff, I found a symetrical ground contact on the driver side were I did the same treatment even though diconnecting this one did not seem to affect the bose amps which were still functionning.

Anyway my scratching noise is still there for a few minutes after turning on the engine.

I also tried to disconnect the audio cables from the back of my bose head unit (the white and the blue connector) and I still have the scratching noise so that would confort me in the idea that the noise does not come from the audio lines but more from the power lines.

Then I was surprised to realise that there are 2 connectors on the back of the bose unit which are involved with powering up the bose amps, not just one like I thought. One connector is single contact with pink wire and it clearly seem to control the bose-amps- power-relay located under the passenger dash ( I can here the relay closing when I connect that pink wire to my bose head unit). But there is another 2-contact connector which also has something to do with the amps because when I disconnect it I have a loud noise and the amps stop working. Could it be that the bose amps have some kind of filtered power supply that is coming from the bose head unit with this 2-contact connector? or is it some kind of counter-reaction back from the amps to the bose head unit?

AGENT 86

That connection is the power source that goes to pink wire for Bose amps.
Your just removing the input, which kills the output.

This is from my 86 FSM, it should help you understand the wiring.

http://members.shaw.ca/agent86/Radio.pdf

bballarin

That's always good to know the end of a story isn'it?

Well, I lived with that cracking noise for all that time since then. I remind that it was only doing it for a few minutes after starting the car, cold or hot. Sometime it was almost gone, but sure enough, I would have it again on the next day.

After checking and re-checking all the grounds, I ended up replacing the ignition module:



But again on the next morning, still the cracking noise after start up.

I do not remember why, but recently I noticed my right door speaker was out. I though I might have a problem with the bose amp and pull the entire speaker enclosure out of the car to discover this was only the speaker that was bad (open circuit tested with the ohm-meter). I could have accessed the speaker by just removing the grille but since I had rebuilt my amps with new panasonic audio grade electrolitic capacitor a few years ago, I though maybe a soldering went bad...

Anyway, put new bose speaker back into the right door and bingo. All my cracking problems vanished.

I am not sure if the speaker has been out for all that time, or if it has been hesitant before failing completely. Anyway i think that the bose amplifiers may generate cracking noise back to the entire system if they are not properly loaded with a good working bose speaker, which by the way are very low impedance, around 1 ohm if I remember well.

Cheers,

Bruno

bballarin

It has been many years, but sure enough I have experienced again the radio cracking noise, particularly while car is warming up.

Recently I unbolted this hard to access "tranny/bellhousing bolt in the upper corner on driver's side" mentioned by jackdaroofer and cleaned all the ring terminals that are hooked there.

Much better since then even though not perfect.

Maybe I'll go once more to this ground point and try to solder/re-crimp all ground terminals.