1987 corvette 4+3 tranny

I have a 1987 vette with the 4+3 tranny, when the overdrive is turned on the dash indicates the overdrive is engaged, but it isn"t. Anyone have a clue where to start to diagnose this problem?

If your question is only about the dash light,
The dash light will come on to let you know that the O.D. is ready to engage. It doesn't mean you are in Overdrive. All the light means is that the engine has met the minimum temp requirement (about 150 degrees or more) and if your O.D. unit is functioning properly, it will activate in 2nd, 3rd, and 4th gears above ~1500 rpm as long as you're not heavy on the accellerator. Hit the gas hard in these gears, and the overdrive will shut off until you reach cruising speed (much like cruise control).

the indicating light goes on/off with the overdrive switch on the shifter but the overdrive does not engage when it is turned on. Is there a relay in this system. I have never worked on this system so any input would be greatly appreciated.

the indicating light goes on/off with the overdrive switch on the shifter but the overdrive does not engage when it is turned on. Is there a relay in this system. I have never worked on this system so any input would be greatly appreciated.

I just looked thru my Chilton manual. No mention of a relay or fuse.

I'll suggest you take a look at the TV cable (throttle valve).

It runs from the back-end of the overdrive unit across the top of the
tranny up to the throttle body lever towards the front of the engine.
You should see two cables attached to the lever, one from the gas
pedal, the other to the OD unit.
Good luck
Mike