Locate the bell wire that connects the wall switch to the garage door opener.
Garage door push button voltage.
The universal remote button kits you speak of are not going to handle the higher voltage associated with the older model opener unless it is powered.
Garage door plug in wireless receiver color sample in white.
The voltage to the sensors is usually transformed at the main opener to low voltage probably dc but maybe ac.
Usually 12 volts dc so your 13 volt reading is likely correct.
Universal garage door opener led light bulb.
Loosen the two terminal screws on the side of the opener where the bell wire attaches using a screwdriver.
Although the bush button system operates on low voltage always un plug the garage door opener and lock the garage door before starting any repairs or work on with the garage door or the garage door opener.
The electrical rep at the home center said the doorbell and garage button are the same.
All available were rated 16v max.
Rail extension garage door openers.
Ratings 179 270 8 0 garage door part accessory type.
Always practice good safety when working on or around your garage door and or your garage door opener.