1998 corvette headlights will not close

3369 Views 24 Replies 10 Participants Last post by dana.james, 4 mo ago

boatman

Discussion Starter · Jun 30, 2021

Hi all,
My 1998 corvette headlights will not close. I have checked the fuses 8,9 and 10. No luck. This morning I noticed that I also don’t have dash lights. But cruise control still works.I cleaned the 2 grounds and replaced the 3 fuses. Where should I check next?

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Mazda77

· #9 · 6 mo ago

autowiz said:
The headlamp control module mounts under the passenger side headlight. With the headlights open you should unplug the motor from the vehicle so it can not close on you. Then remove the plastic bezel from the open RH headlamp assembly and you will be able to see and reach down below the headlamp to the control module. It is a small black plastic piece with 2 plugs going to it. This is the relay that sends power to the motors and sends reverse polarity to close. This is likely your failure. Don't forget to inspect the 2 connectors for water intrusion or expanded pins.

Of the wires running to these 2 connectors..

Black is ground. It needs to be grounded at all times

Orange is power There are 2 of these wires that run to separate fuses in the underhood fuse block and get power all the time

White is the headlamp on signal This should get power only when the headlamps are commanded on

Dark Green is the headlamp off signal This should get power only when the headlight switch is in the off position

Those wires are all in connector C1 and connector C2 has the pair of green wires and the pair of blue wires that go to each headlamp motor. If you are having a problem getting power to the white or green wires when the headlamp switch is in a given state then you obviously have a headlamp switch or BCM/ambient light sensor failure as the BCM can command the headlights on and off with the Twilight Sentinel. If when the headlamps are switched off you have no power on the white wire and power on the dk green wire and power on both orange wires and ground on the black wire then you likely have a failed headlamp control module.

One final test you can perform is to use the knob on each headlight motor to manually run each motor down to the half way position and then retest the operation. There are switches in the motors that break contacts when the motor hits it's point of load/stop and while both failing together would be rather rare, this is an important verification step if we want to make sure we look smart and ensure that we only replace one part to correct the failure.

I am doing a complete rewiring of an 84 for racing purposes but the class requires the headlights to function as it normally would in a stock/street scenario. We swapped out the original three wire motors to the later two wire in addition to replacing the three relay bank with the later controller found in a junk yard. I have also attached a screen cap of the new wiring schematics as installed now.

The entire dash has been replaced with a formed sheet metal replica and the original digital dash has been removed and replaced with analog gauges and all Honeywell NT MIL-SPEC style toggles.

The doors will open but they will not close and I suspect the control module as all the input voltages and switching are correct as per the factory schematic but it is the outputs from the four pin connector to the motors that I see what I consider a problem. When I have the switch in one position or the other, one of the wires for each motor shows a solid 12VDC but the other one shows a voltage of about 11.4VDC and I was expecting to see 0.

To me it seems the internal solid state coil/switch is not functioning correctly. We did have another controller bought at the same time from the same yard and it does exactly the same.

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Mazda77

· #11 · 6 mo ago

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Mazda77

· #13 · 6 mo ago

Triple dizzle said:
Couldn’t you rewire them on a three way toggle switch and reverse polarity. One way up one way down. I mean no more than your going to use them. Manually raise and lower them. Hold the switch until there up and the same for down. Or do the motors not reverse?

In doing the test harness, that is what we determined to adapt by adding the switch to the dash of a DPDT (ON)-OFF-(ON) sprung to center. Just wait for the clunk when reaching end of travel to let the switch go. Headlights must be on when it is desired to move the doors. The high beams will be on by default and the round push-button is lighted so when the desire to flash from high to low for passing alerts, the button would be easy to find in the dark. It is the lower left button on the center panel.

I've also dispensed with the wiper controls with discete switches and a potentiometer scaled as in the schematics to keep all of its functions OFF, Low, Fast in the upper switch, next down id a momentary for pulse and below that the pot for adjustable delayed. Not shown on this page. I use Visio to create schematics with my custom stencil images.

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Mazda77

· #15 · 6 mo ago

It would be my pleasure. My friends are the Corvette guys. I'm just the propeller head. My specialty is mechanical design using Solidworks and then having those manufactured by an array of CNC vendors. They have a small collection of racing Vettes. Right now getting metal panels in the interior of a C2 open cockpit car once raced many years ago. Basically a tube frame car using the original base frame. This one we'll keep period specific to run in SVRA and HSR. A C3 already running and winning with Bobby Kennedy as the driver. Yhis C4 and also a C6 tube frame car originally built for GrandAm GT.

Other than the mechanical stuff, I also do wiring harnesses and a dealer/installer and analyst for Data Aquisition. I was on two GrandAm champion teams in that capacity. 2003 GTS Heritage Motorsports Mustang and 2011 with Brumos Racing. Also did a few years with Stevenson Motorsports in the Corvette built by Tommy Riggins. Tommy and I led that one with Benny Lozano doing the engines. Tht is when I started to produce the tube frame designs in Solidworks so the entire chassis could be CNC cut, bent, notched, holes and slotted by a company near Ontario. The whole thing comes in a box and each tube labeled ready for taking together on a chassis plate.

This C4 is a departure for me as I typically stay away from "stock" construction cars but making the existing Crossfire Injection work with an AEM 308 ECU and fired by a Holley dual sync distributor sounded kinda neat.

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Mazda77

· #17 · 6 mo ago

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Mazda77

· #18 · 6 mo ago

I had neglected to add a picture of the C4 topic.

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Mazda77

· #20 · 6 mo ago

Aircraft but the term used to be for the guys running around with the propeller hats. My full time gig is designing static maintenance and operational trainer for the military. We take decommissioned air-frames and convert them to the latest models structurally. The equipment inside is all simulation copies of the real things in visual fidelity withut any electronics inside but all of the connections and harnesses must be as real so the trainees can get the muscle memory for their tasks. Mostly Blackhawk and Apache but I've work on some other kewl stuff. www.lsijax.com

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Mazda77

· #23 · 5 mo ago

brayanedward said:
If you are having problems with a missing ground at the motor connectors and you have tried 2 controllers you could verify the integrity of that ground and make sure that pin D in connector C2 hasn't expanded.

When measuring voltage on the motor ground wires, when operating the switch from on to off and back, what is the voltage reading for each state of the switch? If you read my posts above about the two wire swap of the old three wire motors, i had the same issues but the "ground" wires would swap between battery voltage and just a little below 12 at about 11.4. I used two multimeters to monitor both at the same time.

The problem is in the ground distribution in the controller reversing relay and I will be testing it to find out if that is the issue. I was kinda surprised to have found an ice cube relay inside the unit instead of solid state. I will let y'all know what I find as we obtained two controllers from a junk yard and both did the same thing even after making sure the ground was good. Now I'll be able to see if the relay is switching without the grounds floating.

If I find the issue and can fix it, maybe a cottage business may be in order.

BTW, the second schematic works perfectly for our needs. The worst that can happen is to replace the plastic gears inside the motor but as this is for racing only, the need to make them work is very limited.

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