Brandonman

2003 c5 59k , twilight setting on but headlight door don't open or close

Having issue with my pop up. Have done some extensive research in this forum and need help to narrow down issue. Either the multifunction switch or the headlight module is bad. Headlight don't pop up or close regardless of using the multifunction switch or with twilight on. Issue is for both headlights that stop opening and closing at the same time

Research so far;
-gear and motor works fine and no grinding. Can move it manually with ease
-all fuse and relay checked both by the battery and passenger footwell and verify with multimeter
-can turn on light with switch stalk but headlight don't pop up or down. All other light works such as interior and running light and etc.
-plastic stop on the motor is fine
-engine ground by the headlight connection appear fine. Have not check the other multiple ground locations
-new battery installed so not low battery issue
-turn on twilight to bypass multi switch stalk and light come on but door don't open or close. Emergency break was off
-when installing a new battery, the both headlights did open when connecting both pos and neg cable. I unhooked the battery and tried to duplicate it with no success. Weird! This also confirm that the motor is working fine.

The one question I have is while the twilight setting bypass the multi switch to turn the light on and open the door pop up BUT DOES IT ALSO BYPASS THE HEADLIGHT CONTROL MODULE? At first I thought the switch was bad but if the twilight fail to open the pop up as well then I am assuming the twilight also require the headlight module to send current/power to open the pop up door.

Side note: I did replace the headlight module with a used unit from eBay but wondering if I got a bad used unit.

One more side note: the issue started when I started the engine after the winter storage and the battery exploded ( battery was on a trickle charge). Not sure if this cause any other electrical problem leading to this issue. Battery burst a little on the side and top with a bang noise. No damage visible to the car engine area

Please help with any insight would be greatly appreciated.

Brandon

Vetteman Jack

Moved to C5 Tech.

Brandonman

Thank you Jack

also, today I add 12 v direct power to the headlight from the battery and was able to open and close the headlight. So something is wrong that is not supplying current to it.

Tsumi

First thing I would check for is the HCM harness. One of the harnesses should have white, 2 orange, a green, and a black wire going to it. Turn the headlamps on and make sure you are getting 12v at the white wire. It would also be a good time to check continuity to ground on the black wire. Make sure you are getting 12 volts at all times on the orange wires. The green wire should have 12 volts when the headlight switch is off.

To make sure that the harness to the motors are good, the other HCM harness consists of a light green and dark green pair for powering the left headlight motor, and the light blue and dark blue pair power the right headlight motor. Try powering the motor through that harness to rule the harness out as a possible cause.

If all of the above check out, you have a defective HCM.

Brandonman

Thanks Tsumi. I will take a look at the harness as suggested. Also do you know if the twilight bypass the HCM? Twilight when enable would turn on the light but not the door. If twilight use the HCM then the problem is with the HCM and or the harness. Currently both multifunctional switch and twilight don't open the dooor.

Tsumi

Twilight mode does not bypass the HCM, it only bypasses the control stalk.

Brandonman

Thanks again. This helps. So this almost eliminate the stalk. If the wire harness from and to the HCM are good then the HCM is bad. Kind if of suck as I just replaced with a used HCM from eBay that could be bad. I will also need to figure out how to test the HCM before buying another one. Will try to tackled the project this weekend I hope and report back.

Tsumi

Orange wires provide power to the headlight motors. The HCM changes direction on the motors by reversing polarity to the motors. It stops supplying power when it detects a surge in current, which electric motors do when they are stalled (stopped by something). Obviously ground is ground. 12 volts on the white wire triggers headlight doors to open. 12 volts to the green wire AND white wire grounded will close the headlight doors. If the white wire isn't grounded, the doors will not close.

UM Rebel made a very good post on how to create your own headlight control module: https://www.corvetteforum.com/forums...ol-module.html
It will definitely be cheaper than a replacement HCM, and probably more robust. Rather than monitoring the current to shut off, it uses a timer.

Brandonman

Tsumi,

checking harness with power to the motor:
-both right and left motor works when power directly to the 12 v battery

checking the HCM harness with the white,orange ,green and black:
-white has 10.83 v with light on. Not the 12 v needed but I don't know if this is ok with 10.83 v? Only have a cheap harbor freight model,multimeter so not sure if the reading is slight off either.
-both orange has 11.28 v when light is on. Has 11.6 v when light is off
-black has continuity
-ISSUE MAY BE THE GREEN WIRE: Green has 0 volt when light is off. You mention that this should have 12 V. Please verify if that is correct. If so this may be the issue , thoughts??????how would thus impact the door to open and close with the HCM?

Brandon
weekend warrior , no mechanical expertise. Knowledge through reading from forum and tinkering.

Tsumi

Not sure what would happen when the voltage is too low. Perhaps try applying 12 volts directly to the white wire if you can with everything else plugged in?

For testing the green, did you turn the switch all the way off? It will also read 0 volts if you have only parking lights on. It will only read 12 volts when the switch is in the full off position. No voltage at the green wire should only affect the closing function, and should not affect opening.

Brandonman

Tsumi
for the white wire, I started the engine with the light on and got 12.94 V. With the engine off I got 10.83 v. Does that seem right that the test should have been done with the engine and light on?

for the green wire, yes the multifunction stalk was all the way off( no running light on and etc.) I tested it again. Both with the light on and off positions and both read 0 volt. I visually inspected the harness focusing on the green wire and there appear to be no damage. Contact are clean of corrosions. If there are no volt to the green wire and as you mentioned it should not affect opening but in my case it does not open or close the door. I'm stumped! Is there a way to get volt to the green wire without having to replace the whole harness?????

Both of my HCM (original and the used one from eBay) appear fine from the outside. No cracks or coming apart that would let moisture in from what I read on this forum for those experiencing bad HCM. Though I did not pry it open to visually check the internal parts.

Thanks again for your help. I believe I'm making progress
Brandon

Tsumi

The multifunction stalk swaps 12 volt power from the green to white and vice versa. You might have a MFS problem, though in my testing the green wire didn't need to be connected for the lights to raise when power is applied to white.

Brandonman

Ok a bit of new info...I was just moving the Vette out to clean the garage and a new thing happened. While the engine was running, I was unable to turn the headlight off with the MFS fully in the off position. Usually I'm able to turn it off without the door closing and engine on. With the MFS off and the engine off, the light then turned off. I tried duplicating it and turn the engine and light on again but this time while the engine is on I was able to turn the light off, you could be right the the MFS is bad.

thanks
Brandon

Brandonman

Just to confirm that I tested the green wire properly. With the multimeter I put the red prob to the green wire and the black prob to the car ground and that gave me 0 volt. Is that correct?

Tsumi

Yep. Green should read 12 volts relative to ground when switch is off.

Brandonman

So I've thinking this whole logic through last night and can't seem to make sense of it

- harness to HCM seem fine other than the green wire with 0 Volt with headlight off but that should not impact door opening but the door don't open

-HCM, the odds are both of them original and the used one bought on eBay are both bad is unlikely

-if the MFS is bad then why won't the door open with twilight on which should bypass the MFS though there are signs that it may be bad. This leads me back to the HCM is bad BUT both of them are bad?

Is there a good way to test the HCM with a multimeter?????




next step: buy a new MFS and hope and pray

Tsumi

If you have some time and a bit of electrical knowledge, I would build the DIY HCM that UM Rebel did. The cost of parts is not that high, just time.

Brandonman

Update, took the MFS off and apart to try and manipulate and clean the internal contact from posts that I read. No luck for me and in fact I made it worst to wear much of the function don't work after playing too much with bending the contacts around. Buying a new MFS from amazon. If this don't work then I can rule out the MFS. Will report back in a few days

Brandonman

Update,
replaced the MFS switch today ( brand new) and the problem is still there.

Summary:
-MFS is not the problem
-HCM is not the problem (unless I got a bad used product from eBay but unlikely if both of my HCM are bad
- questionable green wire from HCM harness reads 0 volt wan dshould read 12v

I'm at a lost and may have to bring in to the dealer for a diagnostic. Trying to avoid this as much as possible. Plan B is to just replace with fix head lights

thanks
Brandon

Tsumi

I don't think a dealer would be very helpful. Try posting in the regional section and see if someone with a C5 can help you out, at least by swapping known good parts.