No lights on A/C panel or stereo

[pipelineaudio]

Hi all, new here

My mother in law just bought an 87 corvette. There are no lights on the A/C panel or at the stereo. I checked for power at the fuse panel on the edge of the driver's side dashboard and everything looks good.

Is there another fuse panel someplace?

Anywhere online with good wiring diagrams?

I'm very used to working on Jeeps, the vette is a little trickier for me

 

[boomdriver]

mother in law? 87 vette?

is she single???
I'll help.!!

before I arrive (lol) check the panels for dead bulbs. its possible that the lites all died together,,,easy fix....install new bulb and have fun!!!!

 

[pipelineaudio]

She's taken

None of the switches do anything, so I dont think its just bulbs

 

[Schrade]

You say the fuse LOOKS good... That's interesting - I've never seen electricity. FELT it, but never SEEN it NOPe.

Put a multimeter in the fuse terminal, see if power is coming in. Then turn on the radio, and see if you can ground 12V through the other fuse terminal.

If no grounding, pull the radio connector input, and see if the 12V is coming into the radio. If not, the short/open is between the fuse block and the radio harness input. If SO, see if you can ID the harness ground. Try to ground out 12V through it.

There could be a dedicated (wire coming out of the unit, to chassis) ground, and also an integrated ground (the radio MOUNT doubles as ground), or only one of the 2. Check FSM. GET one off eBay tomorrow. FIRST repair will cover the cost UH huh.

If you don't have digital multimeter, you can use the ol' fallback analog multimeter in the fuse connector: (yIKEs)

 

[pipelineaudio]

By "looks good" I mean that my DMM showed at least 12 volts on each side of each fuse.

I'll see if I can get her an FSM, but is there seriously no good free online source for diagrams and mods for these cars? I had been using all the google fu I could muster, but havent found too much compared to other cars I deal with.

 

[G Winter]

Do the courtesy lights work? I had this on my 90 ,no courtesy lights also ,and it was a fuse. Some dash items get power from two sources.

Be sure to get both books of the FSM one is an electrical supplement with all the diagrams.

Glenn

 

[boomdriver]

yes, the passenger side fuse panel that houses the main set, that are all marked, will have a courtesy lt fuse that supplies power to the center cluster area. Power needs to be checked at the plugs if the fuse panel checks out. The lites in the doors and cargo area should be on the same circuit.

Look on EBAY for a FSM. if you shop you can get one for under $100 for the set. Some go for as much as $150. A haynes or chiltons manual is worthless. Save the money for the 2 book set. USPS should be delivering mine today or tomorrow after buying ebay for $85.

 

[Schrade]

By "looks good" I mean that my DMM showed at least 12 volts on each side of each fuse.

Okay - there's the problem.

One side brings IN power. The other side completes the circuit, through the switched device, OUT to ground. If you have 12V COMING IN on both sides, that explains why the radio (and something else on another circuit) doesn't work.

 

[navy2kcoupe]

If the fuse is good, then measuring from EITHER side of it TO GROUND will get you 12 Volts.
Best way to measure the fuse is to check for continuity across the fuse while the fuse is out of the panel. Use the meter on resistance (ohms) setting, one meter lead on each fuse terminal, and look for a low resistance (short). If the meter shows a short, the fuse is good.

Andy

 

[Schrade]

If the fuse is good, then measuring from EITHER side of it TO GROUND will get you 12 Volts.
Best way to measure the fuse is to check for continuity across the fuse while the fuse is out of the panel. Use the meter on resistance (ohms) setting, one meter lead on each fuse terminal, and look for a low resistance (short). If the meter shows a short, the fuse is good.

Andy

That's what I was saying - he has to pull the fuse, and test.

If he pulled it, and was showing 12V on both sockets, he then has a short to POWER on the ground side. As far as I know, all D/C circuits are polarized. I don't know if PWM is polarized, and the control unit might have 5V PWM reference voltage.

Anybody?

 

[pipelineaudio]

Just to clear this up:

I placed tested fuses into the fuse panel and checked for voltage at the exposed test pins to ground. Each pin to ground was roughly 12v.

From pin to pin (in order to see if there was a connectivity issue between the fuse legs and the fuse receptacles)was the expected 0v.

I then swapped circuit breakers on the right of the fuse panel to see if I gained or lost any circuits, which I did not

I don't have any Corvette specific knowledge (except that now I wish to all thats holy that my jeep could stop like this Vette!) but I do heavy electronic troubleshooting in my day job.

 

[Schrade]

Just to clear this up:

I placed tested fuses into the fuse panel and checked for voltage at the exposed test pins to ground. Each pin to ground was roughly 12v.

From pin to pin (in order to see if there was a connectivity issue between the fuse legs and the fuse receptacles)was the expected 0v.

I then swapped circuit breakers on the right of the fuse panel to see if I gained or lost any circuits, which I did not

I don't have any Corvette specific knowledge (except that now I wish to all thats holy that my jeep could stop like this Vette!) but I do heavy electronic troubleshooting in my day job.

Both sides of the fuse socket should NOT give 12V, that I know of.

Normally, one side of the socket is 12V, and the other is ground (sometimes through the switched device).

Water is like electricity. Cut the hose, and water won't keep flowing from BOTH cut ends.

 

[boomdriver]

Pipeline,
heres a brief description of the c-4 electronics...

all CONTROL servos, or functions via relay or not, that are controlled by the ECM work by completing the ground path. Power is always there, at the servo. Its the ground path that changes.

Accessories are operated in a more common power on/off fashion. Interior lites should be on the courtesy circuit. Stereo will have power and use its mechanical switch to operate.

basically, anything thats thru the ECM is ground controlled, and everything else is'nt. Typical ECM control voltage is only 5V but it does have a couple 12V inputs.

If that makes any sense so far.....

I have been in the backside of the fusepanel and lived.

Instead of having a "bar-side" with various circuits on the opposite side, it has "banks" of circuits that are divided by the voltage requirements.
So, one side of a fuse MAY have a jumper to others. It is easy to loose a circuit or get voltage that does not belong because of the numerous "hot" wires that go to the back of the panel. The harness is sometimes stressed right there and can pull a hot wire off its terminal leaving that fuse socket dead but everything else works because of the way the wire jumps to the next socket.

What you need is the chart that shows the "shared" circuits. That would show you what got power from that particular fuse, and that would help you isolate the problem. One side of the fuse socket should be to the item it supplies, so it would be dead, and the other side of that socket should be power,and key on or off DOES matter to some things. There are also a couple hidden fuses and relays behind the center display. You might want to pull that bezel and take a look back there to do a visual inspection of the harness and connectors stuffed in there.

I know this is pretty vague to an electrician, but once the C-4 system is understood it becomes lots easier to deal with.

 

[pipelineaudio]

Both sides of the fuse socket should NOT give 12V, that I know of.

Normally, one side of the socket is 12V, and the other is ground (sometimes through the switched device).

Water is like electricity. Cut the hose, and water won't keep flowing from BOTH cut ends.

Maybe this will help

 

[pipelineaudio]

What you need is the chart that shows the "shared" circuits. That would show you what got power from that particular fuse, and that would help you isolate the problem. One side of the fuse socket should be to the item it supplies, so it would be dead, and the other side of that socket should be power,and key on or off DOES matter to some things. There are also a couple hidden fuses and relays behind the center display. You might want to pull that bezel and take a look back there to do a visual inspection of the harness and connectors stuffed in there.

I think this is the secondary fuse panel the manual was talking about. Do you know a write up of how to get in there without busting everything up? This car is still in really nice shape. Is the FSM the only place to get the chart that shows the shared circuits or are there some write ups someplace?

I got the FSM on order from the ebay links posted here, but being the time of year it is now, and the fact that I'm in central Arizona, I'd like to get this A/C going ASAP

 

[boomdriver]

the center bezel is just a few screws, but the main cluster cover has to be loosened at least,. then the center bezel will come out. Once thats off, pull stereo or a/c controls to get working room in the back area. Perhaps if you looked at one thats apart, that would help.
Go to 20th st auto just south of Sky Harbor and see Matt or larry. They will let you go walk back in the yard and look at some cars to help understand what you're getting into. Its easier being able to see whats inside.

 

[Schrade]

Both sides of the fuse SOCKET will not give 12V. Both sides of the FUSE, IF GOOD, WILL give 12V.

The socket is where the fuse plugs into.

If the socket is grounding 12V on both terminals, that is a problem.

(if you know the fuse is good, then the picture you showed is a redundant test)

Maybe this will help