After recently replacing this switch on my BJ8 several times decided to cut one up and see what was inside. Attaching several pictures so you can see the results. Basically this is a very simple device where brake fluid applies pressure to a flexible diaphragm that then pushes a copper disc against several metal contacts closing the brake circuit. Several internal springs hold the disc in place. I originally thought brake fluid might be corroding the contacts but I saw no evidence of this and since I have been using silicone brake fluid I didn't think this likely. Looking closely at the contacts I noticed there was a small amount of hard plastic partially covering one of the contact points. My best guess therefore is this could be the primary cause of early failure. These switches may work when first installed but over time will fail when current draw burns the contact points much like our distributor points. And if one or more of these contact points are partially covered by plastic then they will fail much earlier due to the smaller surface area carrying all the current. This would appear to be a manufacturing defect and not something that a simple initial test would uncover prior to shipment. Although this is a Moss part it is manufactured by Intermotor so please don't interpret this post as a rap on Moss. I've always had good luck dealing with Moss and appreciate the service and support they provide our community.
Replacing these switches is a very easy process. If it wasn't for the fact that brake lights are a critical safety item and the switch failure can occur suddenly and unpredictably I wouldn't give it much thought. I know some of you install inside switches mounted over the brake pedal but was looking for something to keep car original. I did look for alternative switches and was surprised how common they are, particularly as a motorcycle part. But for now will see how my new one works and maybe start replacing it as a normal annual maintenance item.
Hope you found this interesting.
Jim
Replacing these switches is a very easy process. If it wasn't for the fact that brake lights are a critical safety item and the switch failure can occur suddenly and unpredictably I wouldn't give it much thought. I know some of you install inside switches mounted over the brake pedal but was looking for something to keep car original. I did look for alternative switches and was surprised how common they are, particularly as a motorcycle part. But for now will see how my new one works and maybe start replacing it as a normal annual maintenance item.
Hope you found this interesting.
Jim