OK, I have been having an issue with my Wife's 99 Coupe, A4. When you start the car (or even just turn the key on not on acc) the reverse lights light up but very dim.

I checked the voltage in the socket with the bulb out and I was getting a reading of around 8 volts. And obviously with the switch off I read 0 volts.

At first I thought it may be an electrical leak from the Amps mounted on the rear wall but I even disconnected the main power line going to the amps and they still light up.

So I then thought it may be a short in the reverse switch. Well I purchased one but I can not locate the old one under the car. I looked all around the trans for it but could not see it.

Can someone point out exactly where the reverse backup switch is so I can replace it and hopefully correct the issue?

 

If you have a MN6,,, Its on the passengers side of the transmission.

However,,,,,,,,,,,,,,,the switch only connects one branch of the circuit!

You have a more serious issue. There are TWO separate back up light circuits. One operates when you select REVERSE via a switch on the tranny and the other thru the BCM which operates when you unlock the car with the FOB.

Do BOTH modes of operation produce the same dim lights?????

There are TWO back up light fuses.

The Instrument Panel Electrical center, fuse 21 BTS1 BU, 10 AMP That fuse is supplies 12 VDC when the ignition switch is in the ON or ACC position.

Read that fuse to ground and see what the voltage is at the fuse. There are two small holes on top of the fuse, Those are test points. Pick one and read that test point to ground. You should see battery voltage!

Get that far and answer the questions above and I will point you in the right direction once you do the readings.

BC

 

Bill, this quote from OP. "OK, I have been having an issue with my Wife's 99 Coupe, A4."

 

Driver's side of transmission

 

He must of added that info after I replied! Its a good thing that you cover my ***!

Thanks

Bill

 

Thanks guys for all the help here but I'm sort of confused still.. I purchased the Backup Lamp Switch from Corvette Central. There was no indication if it was for and Auto or a Manual when I ordered it. Based on the diagram shown above I still can't see it. Do I have to take that entire linkage off to get to it?

Here is a pic from Corvette Central catalog of what I have.



So I'm still a little lost here...

 

Look at post #4 again. He posted a picture for you.

 

I did see the diagram but I don't see any reference to the backup switch.. Maybe it's me but even after looking at the actual linkage on the car and the diagram I don't see the backup switch.. It is not jumping out at me..

 

The switch in your photo (the part you purchased) looks to be for the manual transmission.

I believe the switch that triggers the backup lights is incorporated in the selector switch in the diagram posted by byronhunter.

 

Timemender is exactly right, maybe this from the service manual will help. I think this calls for more troubleshooting before replacement. If you need a schematic, let us know.
---------------------------------------------------------------------

Park/Neutral Position Switch Replacement
Tools Required
J 41364-A Park/Neutral Position Switch Aligner

Removal Procedure




Raise and suitably support the vehicle. Refer to Lifting and Jacking the Vehicle in General Information.
Remove the intermediate exhaust pipe and allow the LH muffler assembly to hang down out of the way. Refer to Catalytic Converter Replacement in Engine Exhaust.
Shift the transmission into NEUTRAL.
Remove the nuts retaining the transmission shift control cable bracket to the transmission.




Important
Use care to not suddenly jerk the shift control cable during disassembly, the shift control cable rod end guide tubes are EXTREMELY INFLEXIBLE and capable of only a SLIGHT bend.


CAREFULLY release the shift control cable end clip from the transmission shift lever stud.
Reposition the transmission shift cable and bracket.



Disconnect the park/neutral position switch electrical connectors.



Using a wrench on the transmission manual shaft wrench flats (in order to keep the shaft from turning), remove the range selector (shift) lever retaining nut.
Remove the range selector (shift) lever.
Check that the transmission is still in NEUTRAL.



Remove the park/neutral position switch mounting bolts.
Slide the switch off of the manual shaft.
Installation Procedure




Install the J 41364-A to the park/neutral position switch.
Align the two lower slots on the switch (2) with the two lower tabs on the J 41364-A .
Rotate the tool until the upper pin on the tool is lined up with the slot on the top of the switch (1).
Check that the transmission is still in NEUTRAL.




Important
Do not remove the J 41364-A from the park/neutral position switch until instructed.


Install the park/neutral position switch to the transmission manual shaft.
Align the flats in the switch hub with the flats on the manual shaft.
Slide the switch onto the transmission manual shaft until the switch mounting bracket contacts the mounting bosses on the transmission case.

Notice
Use the correct fastener in the correct location. Replacement fasteners must be the correct part number for that application. Fasteners requiring replacement or fasteners requiring the use of thread locking compound or sealant are identified in the service procedure. Do not use paints, lubricants, or corrosion inhibitors on fasteners or fastener joint surfaces unless specified. These coatings affect fastener torque and joint clamping force and may damage the fastener. Use the correct tightening sequence and specifications when installing fasteners in order to avoid damage to parts and systems.


Install the park/neutral position switch mounting bolts. Tighten
Tighten the park/neutral position switch mounting bolts to 27 N·m (20 lb ft).

Remove the J 41364-A from the switch.



Install the transmission range selector (shift) lever onto the transmission manual shaft. Be sure to install the shift lever in an upright orientation.
Using a wrench on the transmission manual shaft wrench flats (in order to keep the shaft from turning), install the range selector (shift) lever retaining nut. Tighten
Tighten the transmission range selector lever nut to 20 N·m (15 lb ft).





Connect the park/neutral position switch electrical connectors.



Install the transmission shift control cable and bracket into position.
Align the shift control cable end to the transmission shift lever stud.

Important
Use care to not suddenly jerk the shift control cable during assembly, the shift control cable rod end guide tubes are EXTREMELY INFLEXIBLE and capable of only a SLIGHT bend.


CAREFULLY secure the shift control cable end clip to the transmission shift lever stud.



Install the nuts retaining the transmission shift control cable bracket to the transmission. Tighten
Tighten the transmission shift control cable bracket retaining nuts to 20 N·m (15 lb ft).

Install the intermediate exhaust pipe. Refer to Catalytic Converter Replacement in Engine Exhaust.
Shift the transmission into PARK.
Lower the vehicle.

 

The above procedure may be a little over my head to perform... I'll try to do what Bill Curlee suggested and report back.

I do know if you put the car into reverse the lights come on full. I just have to check with the FOB on how the lights react.

Thanks Guys...

 

Thanks Bill I'll be trying these steps today after work...

 

OK When using the FOB the reverse lights are bright as they normally should be.

Voltage from Fuse 21 was variable. It was anywhere from 2 volts to 8-10 volts. Never saw a constant voltage reading.

Hope that helps...

 

It sure does help! Now were getting some where!

Remember I was talking about a "MORE SERIOUS" issue, well, thats the case. Fuse 21 gets its voltage from the "IGNITION SWITCH" It comes from the (HOT in ACC & ON) contacts.

If you truly got a good solid connection on fuse 21 and a good ground connection, it indicates that the contacts inside the ignition switch for that circuit are bad. There dirty/arced and making POOR contact. The reverse light circuit draws a good bit of current and that circuit (HOT in ACC & ON) fails faster than most.

So,,heres a FREE FIX! Check out this post:

http://forums.corvetteforum.com/c5-t...ch-repair.html

That should repair your issue. Its NOT as difficult as it sounds.

Before you get too deep into ripping things apart, recheck your meter readings and verify that bad voltage with the key in ACC and then in the ON position..

This is a very common issue.

Bill