Just a thought on what you guys have given me. I replaced a metal one with plastic but saw no grounds attached. Is it possible that somehow the metal original radiator was grounded? I haven't found any ground attached to the old radiator or mount.

 

Don't know if the first went through as I couldn't see it. Just a thought. I replaced the original metal radiator with one with plastic holding tanks. Could there have possibly been a ground from the transmission lines that no longer exists due to the plastic? Just grabbing for straws here.

 

Yes, I have seen that happen. Make sure there are grounds from engine to frame, and engine to body.

 

But the gauge does work normally otherwise, correct?
If so, this rules out something prior to the IVR (instrument voltage regulator) on the back of the cluster. Since the IVR feeds all three gauges (not the ammeter) anything happening with it's power source would effect all three.
So it's either on the back of the cluster in the circuit film, as has been suggested in other discussions, or something that just happens to be coincidentally effecting both gauge sender wires. Which of course, just happen to be up by the front of the engine, near the fan and shroud.
But what do they have in common with the transmission? Normally, nada... But they do run together in the same harness bundle to the firewall, near the shift lever coincidentally enough.
The dash lights dimming could have some direct cause, or just that they're the only sensitive circuit that's visually indicating a small short circuit.

Have you tried turning the lights on before doing the shift test? The dash lights have their own fuse, but the power originates in the headlight switch. Perhaps some of the headlight/running light wires were damaged during the incident? Being right next to the radiator something might have been pinched during the replacement.
Maybe go to one extreme, and remove F2 fuse completely to isolate the dash illumination circuit. See if the gauges still do their thing now.

Will it still act like this when you first fire it up cold? Or is it just that you don't notice until a little warmed up because that's when you first used the gear selector?

Unfortunately, I can't see any correlation between the radio and the other items. The fuses are close to each other at the same end of the panel, but are on separate circuits and don't share their circuits with other things.
So the mystery deepens....

Paul

 

Just wanted to give an update. Had a little time after work so went back out. I ended up adding a ground from the battery to the radiator support and yep, it seems to have fixed it. I'm guessing that the old metal radiator was acting as a ground and by replacing it with a plastic tank one it lost that ground. I really appreciate all of your suggestions very much! I hope that I can contribute somehow now that I'm a member. Thanks again, much appreciated.

 

Thanks for the update. But wow, what a strange one. Which is what usually happens with whacko grounds I suppose.
Usually when you have a strange issue, it's ground related somehow. But yours still seems strange.

Anyway, hopefully the fix is permanent and you won't have to deal with that stuff anymore. Don't see how the radiator-as-ground would effect the oil pressure and water temp gauges though. Since both are in the cluster, and both sensors are in the engine block, it would not seem logical to think the radiator would have an effect.
However, maybe this is without any other body ground? You didn't say whether you found one from the battery negative to the body elsewhere, but if the new one to the radiator core support is the only body ground, maybe it did help.

Paul

 

That is very strange??? Like 1ton said, you must be missing a ground somewhere else causing the issue. They are the biggest pains, your better off adding more to avoid issues like this.