My now-driving-teenage son is the proud owner of a 1984 300D MB in outstanding shape with detailed maintenance records(stereotypical old lady who drove it only to church every sunday)

The only real issue is the glow plug light keeps coming on/off on the dashboard every 30+ seconds when the car is running.

I disconnected both cables from the glow plug box in the engine compartment (near drivers side fender/headlight). However that is not the culprit as the dashboard light would still light/unlight every 30+ seconds.

Is there a relay in line with this? Any thoughts would be appreciated

Normally, the lamp is powered through the blue/white wire connected to the smaller plug on the glow plug timer. If it is still coming on with that connector removed, there must be a short somewhere (like a trace in the instrument cluster) that is allowing current to get to the light.

Removing the lamp would be a viable option; its function is hardly essential.

Thanks for the info

Just checking-The Glow plug timer is the black Box in the engine compartment/drivers side fender/behind headlight-correct?

Correct.