Gearbox indicator interesting issue

[Countachqv]

I am seeing something I never saw before on my black M-DMON: the gear box light stay all illuminated under a certain condition. I can no longer sleep or eat and have PTSD at night because of this. I lost 20 lbs which also makes the car go faster.
But seriously, trying to enlist the sleuth here as to what could be causing this. See the picture below:

Here are the details:
1. I put the ignition key and start. Lever in park -> all lights are lit whether I start the car or not.
2. If I shift to anything and come back to park, the issue is gone.
3. It does not matter if the car is warm or not, just shutting the ignition off will recreate the issue.
4. No flakiness in the issue. Light never flicker or occur in any other condition but the one described above, every time.
5. The shifting is always as normal. No other issues or symptoms, be electrical or else, no code lights, car drives normally.
6. I have a new starter installed a month ago but this issue showed up before that.

[user97]

Interesting.... Are their any codes stored in the transmission. Given that the issue occurs after you start the car, I wonder if you have a transmission/block grounding issue. I would do an experiment -- using jumper cable I would ground the block to the negative post on the body and then start the car. If the problem does not occur then you found the culprit.

[LUNAT1C]

Very curious. It sounds to me like an electronics issue, grounding or transmission sensors. It happened to me once close to 10 years ago in my blue Special, never again after that (though I had the trans rebuilt with a new solenoid pack, clutch kits, torque converter, etc after that).

[FIREM]

This has come up previously, searching found this.......https://300mclub.org/forums/viewtopic.php?f=10&t=3898

so far

[Countachqv]

LOL ​Bob, the other car was self-fixing.. the precursor of smart cars.

I had no code.. No lights.. Alex got this right along with Robert suspicion. I did the ground test and the issue went away. Remove the battery cord ground and issue came back.
So I have to chase the ground wire messed up. Did not really have time but saw a ground wire on the passenger side that is 60% cut. So may be the juice does not flow well. Also despite the new starter, the start is a bit laborious not like the blue car.
Will give the final resolution when I get to it. Right now my lift is taken by the countach. I drained the rear axle oil and realize after draining that the refill plug was frozen too tight (not rusty). Socket chewed up the head. Tried power socket extractor then the G2 socket nothing F.ing works. That plug has a soft head, needs high torque and my extractors all give up and chew the head further. Bad situation, not sure what to do now by my own but that is another story.

[user97]

Glad that you got it tracked down -- my guess it is not the small grounds that bolt to the heads, but rather the starter ground that is partially rotten. Basically what happens is that the starter current cannot flow well through the existing ground and seeks other ways, including range sensor ground, that causes TCM part of PCM see an implausible state of the range sensor, which causes all gear indicators to light up.

I would focus on the big ground wire(s) that go from the block to the remote negative terminal. I have seen them rot in the eyelet. In my experience, I just chose to run an additional ground cable rather than mess with existing ones.

LOL ​Bob, the other car was self-fixing.. the precursor of smart cars.

I had no code.. No lights.. Alex got this right along with Robert suspicion. I did the ground test and the issue went away. Remove the battery cord ground and issue came back.
So I have to chase the ground wire messed up. Did not really have time but saw a ground wire on the passenger side that is 60% cut. So may be the juice does not flow well. Also despite the new starter, the start is a bit laborious not like the blue car.
Will give the final resolution when I get to it. Right now my lift is taken by the countach. I drained the rear axle oil and realize after draining that the refill plug was frozen too tight (not rusty). Socket chewed up the head. Tried power socket extractor then the G2 socket nothing F.ing works. That plug has a soft head, needs high torque and my extractors all give up and chew the head further. Bad situation, not sure what to do now by my own but that is another story.

[Countachqv]

to close this, i fixed it last March. Basically it was the block engine ground wire and i made a description under my Black Car VIN. Both ground were ripped to shreds so I guess the only grounding was the rear one and the battery cable and somehow that was not enough path.