When you jumped 30 to 87 is the starter fuse (30 amp) being powered ??...just check it with a 12 volt test light...if power is going down to the starter you need to check the battery connections not only at the battery but at the engine block ground and at the starter solenoid...86 should receive 12 volts when the starter button is pushed...have you checked that ??...checking the relay terminals should only take a few minutes.

 

Well if its upstream of the Starter Relay then things like the windshield washer pump won't work, the horn, the headlamps they are all on the same B+ Bus bar as the Starter.

If the Relay is fine, the main battery comes off an underhood fuse block with the Alternator, Power Steering, and Fans

 

And FYI the tiny wire on the battery goes to the BCM while the larger one goes to the frame/body which is how everything else is grounded.

 

We haven't seen rain in weeks and today while I have time to check things, it decides to rain. What I was able to check is the 30A fuse does get power with 30 and 87 jumpered. The rain came before I could check 86 with the start button pushed. With a full charge on the battery now, I can here a click from what I believe is the starter but nothing else. I still get the dark display on the dash except for the CEL and a green light on the start button with brake pedal pushed. If I push the start button again with brake pedal applied, all of the displays come up and light stays green. If I push the start button without applying the brake pedal it goes into accessory mode as normal.

The exterior lights work but no horn. I do not know if the horn worked before I got the car. The horn does not work when the alarm is activated but the lights do. The windshield washer works as well. Radio keeps defaulting to on every power cycle even though I turn it off (off not mute). All of the other systems appear to work. HVAC blower, door locks, windows, HUD, etc.

I can hear what sounds like relays clicking in the rear cargo area with the fuse panel and battery exposed.

I'm on weather hold but any other suggestions greatly appreciated. If I don't get anywhere today I'm going to have the owner come get it and have a shop/dealer deal with it. I've got three projects of my own that need my attention.

Thanks again for everyone's help.

 

Well if the horn doesn't work it takes 2 minutes to check with a test light...both the load and control sides are fed from the 350 amp fuse...you can see some of the circuits that are powered by that fuse...these circuits are "hot at all times"...if no power on 2 of the relay terminals check if the 350 amp fuse is blown...if you don't follow a systematic approach to diagnosing this with the wiring schematics and a DMM and test light you will not be successful !!...having a factory level scan tool either OEM or aftermarket will help immensely...I'd STRONGLY suggest to the owner NOT to take a car to an indie shop or dealership...the techs there can't even diagnose a light bulb circuit !!...I've seen it !!...go to an auto electric shop or a diagnostician.

 

Thanks. I have been using the diagrams you posted and using my DMM and test light. As soon as the rain stops, I'll check the latest items you have posted. Unfortunately for us up here in the panhandle we do not have the car culture other areas have so we're limited to local inde shops or one of the two Chevy dealers. It's for this reason, I know longer own an exotic car up here. I played that game with a Ferrari F430 and while the general maintenance I could do, the diagnostics required specialty equipment. The best I could do was an inde in Panama City. If this was my personal car, I would approach things differently but it's not and this all started as a favour to the owner to check it out.

 

Some things are powered both off the underhood box and the rear cargo area. I'd investigate the noise back there.

 

Everything you said that should check hot does. I did get the horn working. I'm pretty sure that the 30A fuse wasn't making good contact as it was pretty corroded. New fuse and now the horn works. The owner is having it towed tomorrow morning. I'll find out where they're taking it tomorrow.

Thanks again for all of the assistance but it's time for me to bow out.

 

Just a quick follow up. Three things contributed to the no start and I'm pretty sure they were all related. The fuse block had lots of corrosion underneath. There was some rodent damage as well but repairable. The starter was bad as well and I think that may have been due to the wiring that the squirrels enjoyed. The car is back running again and thanks to you guys that chimed in (big thanks to C5 Diag) I may have been able to expedite the owner's repairs and saved them some labour costs. I gave the Corvette tech at the dealer everything you guys had me check and the all of the diagrams you posted. Again, I appreciate all of the inputs. It's what makes this forum the best.

 

Glad you got it running !!...the "Corvette Tech" didn't need any input from us...he is supposed to be the EXPERT but then again highly unlikely !!