Reverse light help?

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Apr 15, 2026 | 01:15 PM

#21

lucky131969

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From: Dyer, IN

Quote:

Originally Posted by Hellzgato

Yep,

Test light not illuminated included Key on.. and Key on in Rev. in both of those cases the 87a went from no appreciable Voltage to having the 11.X.. but that 11.X didn’t light the test light no.

I probably probed them 15 times to make sure I was accurate

should 87a be having a signal in Park with the key on or only in Rev?

Quote:

Originally Posted by Hellzgato

I though that would be the signal to engage the relay and should only happen in Rev but it shows the same wether in Rev or Park with key on.

As I explained in post#16, the relay is NOT energized when the KEY is on and shifter is in Reverse. The relay is only energized by the BCM.

I am unable to help you. Sounds like you need to take it to a trusted shop. This is a very simple circuit, they will have it diagnosed quickly. Good luck.

Apr 15, 2026 | 01:26 PM

#22

Hellzgato

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Quote:

Originally Posted by lucky131969

I would rather not start using the word "signal" when you are looking for battery voltage that is confirmed with test light. 87a should have battery voltage when the ignition is "ON", and the shifter is in reverse.

As I explained in post#16, the relay is NOT energized when the KEY is on and shifter is in Reverse. The relay is only energized by the BCM.

I am unable to help you. Sounds like you need to take it to a trusted shop. This is a very simple circuit, they will have it diagnosed quickly. Good luck.

So is the under hood relay the one responsible for FOB approach light functioning? I don't even have a FOB for the car Im strictly hunting down no lights when in rev gear.

Anyway, I appreciate you trying to help very much. We’ll get it figured out. I think I’ll target the trans switch.

Last edited by Hellzgato; Apr 15, 2026 at 07:00 PM.

Apr 15, 2026 | 02:53 PM

#23

Hellzgato

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Can anyone tell me for sure?..

Is the selector switch on the side of the automatic transmission under the car come in to play with the reverse lights?

Meaning, if there’s an issue with that switch under the car, will the signal not get sent?

Apr 15, 2026 | 07:55 PM

#24

helga203

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Quote:

Originally Posted by Hellzgato

Test it and find out. Seems you really want to focus on that switch so check it to rule it out. You literally got help from one of the most knowledgeable electrical helper on the forum.

Probably the other guys didn't need to comment because he went over all the possiblies.

Apr 15, 2026 | 09:30 PM

#25

Hellzgato

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Quote:

Originally Posted by helga203

Test it and find out. Seems you really want to focus on that switch so check it to rule it out. You literally got help from one of the most knowledgeable electrical helper on the forum.

Probably the other guys didn't need to comment because he went over all the possiblies.

Well, I "really want to focus on that switch" because it seems like the only component we haven't really addressed, yet no one seems to say conclusively that it by itself factors into the lights illuminating.. I'll be sure to report back what I figure out.

Apr 22, 2026 | 06:07 PM

#26

Hellzgato

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For anyone who cares. Issue is resolved. A4 Park/Neutral Safety/Rev Lamp switch was faulty.

Apr 25, 2026 | 07:44 PM

#27

grinder11

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I'm glad you got it sorted, and happy you updated the thread. I also agree totally with what Helga said. Maybe sometimes Lucky can be direct or blunt, but he's a real smart guy, and we're lucky (no pun intended!

) to have guys like him, C5 Diag, Bill Curlee, etc., on here...

Apr 26, 2026 | 08:18 PM

#28

Hellzgato

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Oh I agree completely and blunt is fine and productive if you know your stuff which clearly they do!

Just figured id make sure people had an update on what was causing it all.