You can get to the "on/off" switch rather easily, but I'm not sure that would be your problem.
Remove the bottom cover of your 35 RC (three screws), and the leatherette to the right of the lens as the camera is facing you. Remove the single screw revealed, then carefully slide the plate it held from under the top cover, lifting and pulling it away.
Rotate the aperture ring slowly. If all is functioning properly, as you turn the aperture ring, notice that it moves a small white nylon post on the rear of the lens upon which should rest a long chrome switch contact located along the side and above the lens assembly. As the aperture ring reaches it's red "A" setting, the post on the ring should push the switch contact so it is pressed against either a small metal pin contact (original version) or a small "L" contact (improved version) at about 3 o'clock below the lens. This should actuate the meter. Carefully clean this post or "L" contact, as well as the long chrome contact where they touch to assure proper conductivity.
When properly adjusted, and the aperture ring is rotated fully counter-clockwise to the "FlashMatic" (lightning bolt) setting, the end of the long contact should still rest against the nylon post without any space between them. Then, as the aperture ring is turned to the red "A", this nylon post should press the contact until it touches the post or slips beneath the leg of the "L" contact, then separates as the dial is turned to the "OFF" setting and beyond.
Often, however, the long contact will slip over the roller and become crunched into a zig-zag pattern as the aperture ring is turned from the lightning bolt to the manual settings. If this has occurred, it is possible to carefully straighten the contact, but it can be very frustrating. Your best option in this case is to have a functional RC body to observe and mimic, straightening the contact and adjusting it so that it functions as described.
If this does not correct erratic exposures, the problem may be with the battery contact. This is also a difficult problem to address. The battery chambers of RC's are becoming quite fragile and can melt or fracture easily, and replacements are unheard of. Attempting to remove or solder to the battery terminal may result in destruction of the chamber.
The wire connecting the circuit to the battery contact is soldered to a tiny brass bolt on the underside of the battery chamber, and corrosion frequently develops between this bolt and the screw seen holding the battery contact. If cleaning the meter switch doesn't work, you might try gently turning the screw holding the battery contact in place slightly back and forth a few degrees. This may allow better connection between the contact, screw, and brass nut.