1986 C4 with dashboard backlight problems

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Jul 4, 2007 | 10:58 AM

supersapper1

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7th Gear

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From: Sterling Heights MI

1986 C4 with dashboard backlight problems

I just put an aftermarket radio into my 1986 Convertible and now I'm having a problem with the dashboard lights. When I turn the lights on, or when the car is in the dark, the dash board will not light up. I'm sure this has something to do with the removal of the stock radio, but I dont know where to start. To connect the aftermarket radio head, I used an adaptor harness to connect the radio to the factory radio harness. Any ideas?

Jul 4, 2007 | 11:04 AM

jfb

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From: Cincinnati, Oh USA

Check your 3 amp inst fuse it might be blown. Your aftermarket radio backlights may draw so much current that it blows the inst fuse which also supplies power to the backlights of the cluster, telltale, wiper, header map light, heater a/c, automatic gear shift.

Jul 4, 2007 | 12:00 PM

DrEvil11417

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From: Howard Beach, NY

Quote:

Originally Posted by supersapper1

if i recall the wire that controls the dimmer is a grey one

Jul 4, 2007 | 01:05 PM

supersapper1

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7th Gear

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From: Sterling Heights MI

Quote:

Originally Posted by jfb

I thought fuses too, but I've checked them and there seems to be no issue there. I do have backlighting on the heater/ac, and gearshift. All other controls operate normally as well. I can turn the dome lights on with the dimmer/headlight switch, do I dont think it's that either.

I was reading earlier about how the stock radio controlled the dimming function on later model corvettes. Is this true in 86 and if so, how can I bypass that function? I dont care if I'm not able to dim, but I do need to be able to see the gauges.

Jul 4, 2007 | 04:00 PM

jfb

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From: Cincinnati, Oh USA

The 86 radio has no control over backlight dimming, only the headlight switch has control AND the photoresistor in the cluster controls the backlight dimming. Unplug your radio adapter harness and see if you have backlights again. If so, your adapter harness is the fault.

Jul 4, 2007 | 04:01 PM

jfb

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From: Cincinnati, Oh USA

Jul 4, 2007 | 04:51 PM

CentralCoaster

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From: San Diego , CA Double Yellow DirtBags 1985..Z51..6-speed

Not sure if this is the cause, but:

You cannot use the dash light dimmer circuit with your new stereo.

You have to wire it to the headlamp illumination circuit. The dimmer circuit uses a potentiometer in the headlight **** to decrease voltage to the incandescent dash bulbs.

Your new stereo uses LCD and should not be tied into the dimmer circuit.

The cluster uses the headlamp illumination circuit, the dimmer/potentiometer circuit, and the light sensor. Your new stereo will use only the headlamp illumination circuit to control the display, bright (headlights off), or not as bright (headlights on).

Last edited by CentralCoaster; Jul 4, 2007 at 04:54 PM.

Jul 6, 2007 | 08:26 AM

supersapper1

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7th Gear

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From: Sterling Heights MI

Quote:

Originally Posted by jfb

I took out the radio and reinstalled the stock radio and still could not get the backlighting to work. It was working prior to me installing the new radio so I refuse to believe that the dash panel is bad. The dimmer and the illumination circuit both are not connected to the new radio anyway, so I dont think the problem is there.

How does the photoresistor work in this era vette? Does it automatically sense ambient light to determine how bright to set the display? Can I bypass it's functionality to I can get the backlighting to work on my instrument cluster?