chevylu

When you disconnect and then reconnect the negative battery cable to the battery, does your Corvette’s left hand (driver’s side) headlight motor run for four seconds and then stop?

Before I go further, I need to point out that the headlights and the headlight door motors on my 1990 Corvette work; that is, they open and light when they should and close and extinguish when they should. The left hand motor runs longer than the right, however, both when the door opens and closes.

In the process of disconnecting and then connecting the negative battery cable to the battery, I noticed the left hand (driver’s side) headlight motor will run for four seconds and then stop. The right hand headlight does not do this, only the left. In the past, I had noticed this anomaly, but at that time I did not give it much thought, assuming it was normal. In retrospect, now I believe that the left hand motor probably has a limit switch issue.

Recently I began troubleshooting a particularly frustrating parasitic battery drain problem. The frustration stems from the fact that the battery discharge is intermittent; that is, most of the time the battery does not discharge, however, every once in awhile it does and will not start the engine. The battery itself is less than a year old and I have had it tested: it’s good.

In order to determine if the parasitic current draw is within specifications, I disconnected the negative battery cable and inserted an amp meter between it and the negative post on the battery. According to my FSM, the total load should be 14.9 milliamps @ 12.6 vdc when the CCM is asleep with the key out of the ignition.

Digging a little deeper with my amp meter, I discovered that that when the left hand motor runs, it draws a brief surge of 13 amps and then runs at 1.5 amps for a period of four seconds. I also checked the resistance of both the left and right hand motors at the connector plugs; they both read 1.5 ohms.

At this point, I disconnected both the left and right hand motors at the connectors and checked the total load; it is 12.4 milliamps. Looking at the FSM specifications, I believe this is as it should be as this should effectively take the Headlamp Door Control Module (2.1 milliamps) out of the equation; that is, 14.9 – 2.1 = 12.8 milliamps. That’s quite close to my reading of 12.4 milliamps.

From FSM pg 6D1-4

Load Name Milliamps
ECM Memory = 2.5
HVAC Control Head = 0.2
HVAC Programmer = 4.8
CCM Asleep (Key Out) = 1.4
Headlamp Door Control Module = 2.1
Generator Output = 1.1
Chime Module = 0.8
Radio Control Head = 0.6
Radio Receiver = 1.4
TOTAL = 14.9

Searching this forum for battery drain problems, I found that many posts referred to faulty relays. Given this list of of relays of whose existance I am aware, does anyone have any suggestions for finding an intermittent drain?

Horn
Fuel Pump
Dome Lamp
Fog Lamp
Radio Speaker Amplifier
Antenna
Starter Motor Interrupt
A/C Compressor
Low Blower
High Blower
Primary Fan
Secondary Fan
AIR Pump

janarvae

My '91 headlights don't and they work perfectly too.

vetteric

Don't know about your battery drain, but your left headlight problem is probably due to worn headlight bushings. I've had this problem in both headlights and replacing the bushings cured the problem both times.

bikertrash2001

My '92 did EXACTLY the same thing. It's as if the motor won't park completely because the bushings were shot. Got a gear and bushing kit and replaced the desentigrated bushings and now it parks just fine. I was disconnecting and reconnecting my battery while I was working on the starter.

chevylu

Thanks Biker; that's kind of what I thought was going on. Your post confirms it.

It looks like I'll be taking a trip down shrade's path: http://forums.corvetteforum.com/show...pair+headlight

It's been a busy summer working on my 18 year old car; one damn thing after another! I thank my lucky stars (or forum stars whatever the case may be) I found this forum.

Now if the stars would help me find the battery drain, I'd be good to go until next year.
...

bikertrash2001

The one thing I found was that it was not necessary to completely remove the motor from the motor/gearbox assembly. I just needed to loosen the two screws holding the motor to the gear housing and let it slide just a few mm's.

chevylu

That's a good tip. Thanks.

rodj

Had same problem , not engaging limit switch.
If you try turning the manual **** when it is "parked " you can feel motor trying to drive against you.
The armature "floats" and when loaded at either end of travel is supposed to engage limit switch