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Electric short no courtesy lights


Dec 5, 2009
charlotte, mi
1993 Ruby Red
Having problems on my 1993 ruby with no courtesy lights. I am gettin power on both sides at the 5 amp fuse and on each lamp socket. Relay is ok. Was also getting power on white wire of light switch connector. When I grounded the white wire on the courtesy light socket the relay would buzz. I thought about disconnecting the white ground wires at each connector anreplacing it with a new wire to a ground of its own.


Site Administrator
Staff member
Sep 16, 2000
New Hampshire
1990 Corvette ZR-1
Moving out of the New Member Introductions forum and into the correct C4 Tech forum...


Well-known member
Aug 30, 2013
Minneapolis, Mn.
86 Red Convertible
Something I found on the earlier C4's regarding that relay. If you can turn the headlight knob and the lights turn on but not when you open the door etc, it's likely the relay. In the 86, I've read if you remove the relay and connect the 2 white wires the lights will go on and off when the doors are opened and closed.
From the sound of that info, it sounds like one of the 2 white wires has power applied to it while the other goes to ground.


Well-known member
Sep 3, 2004
Bluffton, Indiana
2000 Black Coupe; W/6-Speed
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Active member
Oct 11, 2007
The 93 system is very different from the 86 system. The 86 system has a solid state relay/controller that is notorious for failing. The 93 does not have such a controller.

The 93 has a CCM. ("Body Controller"). The door switches are inputs to the CCM. The CCM controls the dome light relay through one of its outputs. The CCM's inputs and outputs can be monitored and cycled using the Trip and Fuel input panel after shorting two terminals in the ALDL. The technical resources section of this site has the details of how to use the on-board diagnostics in the CCM. Very powerful and cool.


Well-known member
Jan 7, 2003
Ocala, Florida
1993 Blue
Information on courtesy lights...

Some useful information on the 92-93. It helped me troubleshoot mine.

The '90-'96 Corvette courtesy lights are controlled by the CCM (cen- tral control module) located in the dash behind the radio receiver. The courtesy lights are set-up with a delay when entering or exiting the passen- ger compartment; The courtesy lights are also designed to turn off after ten minutes when the doors are left open to avoid battery drain. If the doors are opened and closed in the ten-minute time period, the timer starts all over again. Courtesy lights should not
come on at any time when there is enough ambient
light available to sat- isfy the light sensor in the dash. The light sensor is located in the DIC (driver information center) at the upper left corner. Courtesy light on input signals come from the door ajar switches, door lock key switches (when going from the locked position to unlocked), headlight switch (moving
the instrument cluster dimmer switch to the top), and the ambient light sen- sor. Once the CCM gets a signal from a door lock key switch, it processes the info and then latches a courtesy light relay located behind the passenger side of the dash, but only if the ambient
light sensor senses low-Iight conditions for illuminated entry. If the door was unlocked upon entering, the door ajar switches provide info to the CCM with- out involving the door lock switches.

The ambient light sen- sors come into play after input from the door ajar and lock
switches. After
the PKf {passive keyless entry} system became
involved with the cour- tesy
light. The PKf sig-
naled the CCM that the door was unlocked and
the courtesy lights should be on in
low ambient light conditions. Beware! This same situation may apply if an aftermarket alarm system was
installed on
a '90-'92 Corvette. If you have an aftermarket alarm system, check there first.
Now that we have an idea how the system works, let's see if we can figure out what's causing the problem. The first place to check is the CCM for possible codes relating to the prob- lem. You can enter diagnostic mode by grounding terminal
G to A in the ALDL {assembly line diagnostic link} connector under the driver-side dash panel. The ALDL points downward and is about where your right knee would be while seated in the driver seat. ALDL Terminal A is at the top right corner and terminal G the lower left corner. Use a jumper wire to connect terminals A to G, and then turn the ignition switch to the ON position. When the key is turned on, fault
codes will be displayed automatically in the speedo LCD screen. The module number will be displayed in the left center of the LCD starting with mod- ule
1, which is CCM data. The next module displayed will be 4 fCM {engine control module} codes and finish with module 9 displaying ABS/ ASH {antilock brake system/acceleration slip regulator}
and fBCM {electronic brake control module} codes. The codes will have an "H" for history codes and "C" for current codes, meaning the problem is occurring right at that moment. After any codes are displayed for a
module, the screen will display
,,-- " ending that module interrogation and going on to the next module. If you miss the codes the first time, you can turn the ignition key off and then back to the on position and the codes will display again in the automatic sequence as long as the jumper wire is in place on the ALDL. There is also no limit to the number of times the codes are displayed.
Once you interrogate the CCM, you may find code
24, indicating a shorted courtesy light relay coil or CCM internal open circuit or code 25, which is a courtesy lamp relay coil circuit open or shorted to ground in the CCM. If you find a code, make note of it, then you can select the
CCM cycle inputs function by repeat- edly pressing the TRIP/ODO button in the DIC until
"1.3" is displayed in the trip monitor area of the speedo LCD screen after the automatic code sequence has finished. Once you're there, press the ENG/MET button until "04" is displayed in the odometer area of the LCD. This is the right door ajar input. If you pass "04," you can go back by pressing the FUEL INFO but- ton. When the door is opened, "I" should be displayed in the LCD odometer area and then "0" when the door is closed. If the door is open when you start interrogating the sys- tem, "I" will be displayed and then "0" when closed. After testing the right door ajar, go to "05" left door ajar and do the same test. This will tell you if the door switches are working properly; and if the CCM is
processing the info correctly. If the correct info is displayed, the door switches, wiring, and CCM is process- ing the info correctly.
The most likely problem is a mal- functioning door lock key switch, especially if it's used often. There will be no code for this problem, but can be tested while performing the input tests. Go back to test 1103'1 in the input tests. A "0" should be displayed until the door key is inserted and turned to the unlock position. The display should be showing a "1" in the unlocked position then back to "0" when the key is centered in the door lock. If the display shows "1" all the time, you have found the problem.
The door panel will require removal and door lock cylinder key switch replacement.
If that didn't fix the problem, the next step is to see if the courtesy lights can be controlled by the CCM manually; We can cycle the courtesy lights
through the CCM output test. This tests the courtesy
light relay operation,
wiring from the CCM to the relay and wiring to the courtesy lights. Select the CCM cycle output function by pressing the TRIP/ODO button in the DIC until "1.4" is now displayed in the LCD screen. Once you're there, press the ENG/MET button unti11110'1 is dis- played in the odometer area of the
LCD. If you pass "10," you can go back by pressing the FUEL INFO button. When 1110'1 is displayed, the courtesy lights should go on and off in approxi- mately three-second intervals. If the courtesy lamps stay on during testing, I would check the relay under the pas- senger-side dash for possible sticking contacts. Remove the carpeted lower knee-bolster panel on the passenger side of the dash to access the relays.
The panel on the passenger side of the dash that houses the fuse panel must be removed to remove the lower knee- bolster panel. There is one tmm screw hidden behind the fuse panel bezel for the lower panel. The courtesy light

relay would be the second relay from the passenger door side of the dash. There is a bank of five relays attached to a piece of plastic channel that runs parallel with the dash. Once the relay is pulled, the courtesy lights will be off unless the headlight switch is causing the problem. When the headlight
switch instrument dimmer rheostat is in the fully up position, the ground circuit to the courtesy lights is completed, bypassing all of the aforementioned components. All of this info gives you a good idea of what goes on and should point you in the right direction.
If the door ajar info was correct and pulling the relay turns the courtesy lights oft; try a relay. If the relay isn't
the problem, the CCM is grounding the relays gray/black striped wire, which could mean CCM replacement. It's dif- ficult to access the relay and even more difficult to check the wiring in the relay socket, but to know for sure that the CCM is the culprit, the gray/black wire would need to be checked for ground. There is a possibility the gray/black
wire is shorted to ground between the CCM and courtesy light relay. If the gray/black wire is grounded all the
time, the CCM would require access behind the A/C Controller and the radio. At this point, a factory service manual should be used to further test and access the CCM.


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