[Doctor john]

1967 LeMans with warning lights, not gauges. I restored my dash and replaced bulbs. Should all indicator lights illuminate when key is placed in accessory position? I only have generator light illuminating I accessory position, not oil pressure or temp lights. Do they need to be incandescent bulbs or can I use LEDs?

[Mister Pontiac]

Funny, but I can't recall 100% if the Battery light comes on in Acc position. I think all lights should be out.

You can use LED's in the Temp and Oil lights, but I believe you want to keep incandescent in the Battery light. Seems an LED messes with proper operation (or I could be recalling my 72 having that issue).

I'm sure someone will chime in with the complete accurate picture.

[OG68]

Only the Battery light comes on in ACC position and then dimly.

Oil Pressure and Battery come on in Run (engine not running). Oil Pressure using the sending unit for the ground path. If you crank the engine long enough, then return to RUN without starting, the OP light will be out as the engine built pressure even though it hadn't started yet. It will then come back on as pressure drops back to zero

The Water Temp operates in Start but not through the sender but through a ground circuit incorporated in the ignition switch since the temperature sending unit switch doesn't close to ground until 235* or so.

Current flows through the battery light in both directions depending upon whether the ignition switch is in ACC or Run.
In the ACC position the BAT light receives power through a brown resistance wire and grounds through the oil pressure light circuit which is why it's dim in the ACC position. In RUN it receives a full 12 volt and grounds through the alternator. It's a slightly complicated circuit to follow but works quite well if not modified.
Since a conventional LED only lights up if power is applied to its positive terminal the BAT light will only operate in either ACC or RUN depending on how the bulb is installed. This is why it needs an incandescent bulb.

IIRC Chevrolet models use the resistance in the incandescent bulb for VR operation.