Grey87

I spent some time searching, but did not find info specific to where I am with this problem;
*Dash illumination goes dark when I turn on the lights (normal in daylight). Took the dash out and ended up sending it out for repair via local Corvette specialist dealer.
* Paid $350 to have unit "fixed". A couple of problems found and repaired. Put dash back in - same problem.
* Checked back with local Corvette dealer. He checked with place that did work on cluster. They said they found a few problems, fixed and tested cluster and it worked correctly. Suggested I replace the headlight switch, based on fact that they had me check to see if the lights for the centerstack (guage switch lights) did not work either.
* Bought and replaced headlight switch. Same problem!
* I then made up a ground wire jumper and connected that to the #1 position in each dash cluster connector and ran ground directly to the battery ground. Same problem - dash goes dark when lights turned on.
* The light sensor "seems to work" correctly. With lights off, dash is bright. If I block light in front of sensor, dash dims according to amount of light available.
With headlights on, I can shine light at sensor and dash illuminates. Remove light and dash goes completely dark.
* Any merit to removal of Bose system affecting dash? I have replaced with new aftermarket system.

Thanks for any help!

engle1147

Bose removal will not do a thing to the cluster.
Most cluster tester equipment machines do not include a headlight switch for test purposes...pretty clear why they would miss this.

To me it sounds like the voltage divider within the photocell is bad. Replace the cell then retest for functionality.

383vett

On my 84 the dashboard will be dark if the ground wire (one of 3 on the driver's side bellhousing) is not connected.

Hooked on Vettes

When you turn on the headlight switch to Head or Park and the back lighting is missing for the Windshield wiper switch, Tell tale display, Header map light, Heater and AC control head, PRND inidcator for auto transmission, back lighting for the radio (which may not apply since you have an aftermarket radio) and the dash cluster, the INST LPS
3 amp fuse is probably blown.

You should post the name of the company you sent the cluster to for repair. Charging you full price for something they probably found no problem with is a rip off.

Grey87

HOOKED ON VETTES; I checked the fuse and it was blown so I replaced it, but it did not resolve the problem. Thanks for your input!!

383Vette: I had created a ground jumper, plugged it into each ground location on both connectors, then ran it to the battery ground, but to no avail, but thanks anyway.

Engle1147; You state convincingly that removing the Bose should have no effect on my problem, but during my research on the web, I found more than one reference that indicated that removing the Bose might create a problem with the dash not illuminating when the headlights were turned on. Can you elaborate?

Right now I'm looking at two options:
* take out the Kenwood unit, put the old unit back in and see if the problem goes away. Then I would need to get in touch with either Kenwood or Crutchfield and see how I need to modify the connections for the Kenwood to get the dash back when the lights are turned on.

* remove the dash and send it back to the company that "fixed" it. They will bypass the sensor for free. The dash will then always be "ON" at "full bright"

Thanks everyone for the help. Any more suggestions would be appreciated!!

Hooked on Vettes

If the dash cluster back lighting worked properly before you installed the new
radio, you most likely wired the radio incorrectly. Most aftermarket radios do not
use the factory dimming circuit.

Since your INST LPS fuse was blown, that indicates there is a problem in the
dimming circuit. If you look at the factory plugs that the Bose radio used one
of the connectors has a Gray wire. That wire should not be used for your
new radio.

After you installed a new fuse, are you sure it didn't blow again?
There is no power to the fuse until the Headlight switch is in the
Head or Park position.

You need to verify with a volt meter or test light there is 12 volts at
that fuse or the Gray wire when the Head light switch is in the Head or Park position.

The actual voltage at the INST LPS fuse or Gray wire will depend on the position of the dimmer switch.

Also verify when the Head light switch is in Head or Park, the tail lights work.
If they don't that would indicate the Tail fuse is blown.

Here is the schematic for the dimming circuit.

Grey87

hookedonvettes;
*The tail lights work
* The new fuse did not blow
* I used a test light and there is no power to the fuse when the lights are on.

I guess I'll have to pull the radio and see what I did with that gray wire.
If I have the gray wire connected, should I just dissconnect and tape it?
Does the fact that I get no power to that fuse that the gray wire is most likely being used?

Then what?!?

Hooked on Vettes

If the tail lights work that indicates the Tail fuse is good.
The Tail fuse supplies the 12 volts to the INST LPS fuse when the Headlight
switch is in Park or Head.

A Dark Green wire from the Headlight switch goes to one side of the INST LPS fuse.
The other side of the fuse is a Gray wire which is the dimmer signal and goes to the
light bulbs to control the back lighting of the dash cluster, AC control head, Tell tale
display etc...

The actual voltage on the Dark Green wire and Gray wire will depend on the position of
the dimmer switch.

If you don't have a volt meter.

Rotate the Headlight dimmer switch all the way clockwise and turn the Parking lights on.
See if the test light lights at the INST LPS fuse. If not, rotate the switch to the counter clockwise position but not past the detent position where the interior lights come on. See if the test light lights at the INST LPS fuse.

If the test light still doesn't light, remove the INST LPS fuse and with the Headlight switch in the Head or Park position, verify again at each prong where the fuse was if the test light still doesn't light.

The test light should light on one of the prongs. If it doesn't there is a wiring problem
from the Headlight switch Dark Green wire to the fuse box INST LPS fuse.

If the test light does light on one prong the INST LPS fuse is blown again.

If you have the Gray wire connected for your new radio, just cut it, tape up the end and don't use it.

Did this back lighting problem occur after you installed the new radio?

Grey87

Hooked on Vettes;
I proceeded with your troubleshooting suggestions and found that turning the headlight switch ALL the way counterclockwise - just to the point of turning on the interior lights - the dash (and the guage switch lights) illuminates!!
Now, if you move the switch a very fraction of an inch clockwise, and I mean a tiny fraction, it goes dark. And this is a new headlight switch.
Also, the switch doesn't "lock" when you turn on the interior lights, you have to hold it, but I think I will live with this for now. At least I have a lighted dash for night driving.
I have had the dash apart so many times with installing the new stereo system and this dash problem, I'd like to get some use out of the car!!

To answer your question, yes the problem seemed to appear after I installed the new system. But I can't state catagorically that it caused the problem as I used the car several times for day trips before that fateful trip where we were out until after dark.

I thank you very much for the assistance. If it wasn't for this last procedure you posted, I probably wouldn't have found the "solution", even though I had turned that switch several times before, but just never hit that "sweet spot" I guess.

Hooked on Vettes

When you have some free time, put the original Headlight switch
back in.

Appears most replacement electrical parts are made overseas.

I purchased a AC Delco relay for my cooling fan and it was
made in India.

Grey87

I was thinking about putting the old switch back - or - going back to my Corvette guy and get another switch. It just doesn't seem to have the same quality as the original. It's action is rough, not smooth as you would expect.
By the way, I did get the interior lights to "click" on this morning. I just had to turn the **** a little harder than might be expected. I was afraid I might break something! Maybe I just need to work the switch a bit to smooth out the action.

Thanks again for your help!

clusterman

Hi, I live in PA and I had a similar issue with my 89 vet, except that the entire instrument cluster has gone dead, though sometimes it lights back up but the speedo is in-operable
anybody have any suggestions?

wbenning

I have the same issue, I have 12v to the INST fuse with the headlight switch pulled out, and as soon as I pull it out the fuse blows.

I have no clue if i have a short on the grey wire i guess it is time for a short circuit detector. unless anyone knows of a normal fail for this INST fuse