When you say the up arrow, is that the amber upward arrow that is controlled by the o/d switch on the shifter handle?

My newest is a 1988 244GL, there may be changes in your model, I dunno. But, many things stay the same, too.

The amber arrow indicates that the automatic trans has the o/d inhibited. If the lamp is lit, the trans will NOT engage the o/d even if the speed and throttle position warrant.

This is backwards from the M-47 cars, where the green arrow means o/d WILL engage if the trans is in 3rd gear, regardless of road or engine speed.

Your problem seems related to engine speed and electrical things. Have you checked the alternator brushes? They need to be 5mm or longer to do the job. Less that that and the alternator may be restrained from producing a full charge unless the engine is revved up. This situation should be hard to spot unless the battery is about dead. Any evidence of that?

The radio with a mind of its own is sort of an oddity. If it persists, get a good aftermarket unit.

Good Luck,

Bob

:>)