[Mr70]

Basically A styrofoam float followed the level of the windshield washer fluid.
A paddle having a green & red lens on top of it would shift in front of a dimly lit bulb.When the level was low the color red would illuminate.When it was full,the color green would illuminate back into the sight lens mounted under the dash,notifying the driver of this.All this via a fiber optic line.
This option actually had 3 different designs,all varied on what time period throughout 1970 you received it in.
You could order it seperately as RPO CD-2,or with the Auxillary Lighting group as ZJ-9.