Can brake light switch fail due to air bubble?
 

What if the switch is fine, but there is an air pocket in the switch?
Is this possible under this design?

Also, does the brake light switch removal potentially introduce an air bubble bleeding scenario?

I would think the bubble would float up and into the brake fluid container, wouldn't it? I've replaced those switches on my 87 and 88 cars and I'm pretty sure I got at least a little bit of air in the system when I did it but still have normal brake pedal pressure afterwards. I still think it's not the best design..some have bypassed the hydraulics.

I do not think the switch would be impacted by air in the system. Pressure on the system from applying the brakes would move the fluid and the bubble, through your lines. Bleed that. The switches, however, fail often. Easily replaced. They are redundant, btw.

Refresh the initial problem….was there an issue with the dash Brake Warning Light coming or staying on?

I had Brake Warning light come on, flicker, turn off and no adjustment could get the light to turn off, I found the contact band on the handbrake level had broken and occasionally would make contact with switch and turn the warning light on.
Second instance, sat on very steep incline and that triggered the Brake Warning to stay on. Checked the level of the fluid but it was full. Decided to flush the system, clean the reservoir and warning light turned off.

You can remove the reservoir and not introduce air, I expect the same with the two switches since they are in front of the brake lines and any air space will come to the top as was stated in previous comments.

Lastly the rubber brake lines if very old could be swollen and obstructed causing the warning light, crud accumulation in the system and old fluid with substantial moisture rusting out the switch or two.

Disregard a few comments above - I found your earlier post, I misunderstood - it’s a problem with the rear exterior Brake lights.

2 years ago, my brake lights stopped working
I replaced one of the switches, with a cheapo $8 switch, and that fixed it.
Now, lights not working again.
Gonna replace switch and see if that solves it

There was a post here suggesting to put some pressure on the brake pedal with a stick to prevent air getting into the brake system when replacing the switches.
Also put a drop of brake fluid (from your brake fluid reservoir float) into the hole at the top of the new switch; shake it and tap it until the fluid gets in / a bubble of air comes out. Repeat, and use a small pin to help the fluid in. Repeat once more, now the switch should be 'full' - keep vertical.
I did both of those when I recently replaced my switches and I had no issues.

I fought with this for quite a while before I finally just broke down and put a relay into the circuit.

Thanks to a member on this list who cut a failed switch in half, it appears that they fail as they get corrosion on the itty bitty contacts inside the switch from switching the relatively high brake light current all the time.

On my previous car I put in a relay which lasted then rest of my time owning the car (10 years) while I had gone through 4 sets of switches in less than 5 years previously.

The relay I use is just a standard Bosch relay....nothing special, here is the circuit as is installed in my car. Note that I do not use the 1989 warning light system as the dual switch and cross-wiring design used by Porsche alerts you to failure of one brake hydraulic circuit - if one switch closes and the other does not, it illuminates the brake warning light.

http://forums.pelicanparts.com/uploa...1719941453.jpg

Hope this helps

D.

I switched out the 3 year old switch for a Beck/Arnley 201-1087 Stop Light Switch.
The brake light is now working. Was not air bubble or bleed issue.
So, the cheapo switches fail fast.
Can't remove front switch since its blocked by brake line.

What a nightmare of a simple repair.
Remove carpet, remove shield,
detach cross brace (annoying bolt access at bottom)
detach 2 hoses, detach electrical plug,

22mm switch is so blocked by stuff.
1/4 turn at a time.
Back on fire

Getting air hose re-attached was also a hassle b/c it's not clear if the underside is seated.
Electrical plug also gets in the way.
I also started to attach the cross brace to the wrong screw hole (for back shield)

...yes it is a pain on both ends of the spinal cord, hence the relay solution.

The key was understanding the failure mode as being minor corrosion internal to the switch, in some ways analogous to the problem with the high beam stalk...too much current for too small of a contact promotes corrosion.

I swore on a stack of Bibles that if it failed again, I'd be doing some sort of manual switch, but it never failed.

I did make sure on the project to route the brake line so both switches have a fighting chance to get out with a socket....still a pain though.

D.

How did you reroute brake lines?
Seems like a major detour in the project

No, not as big of a change as you might think..

Since the car was completely stripped, I had easy access to the brake master cylinder area.

I took the brake lines from the MC and bent them slightly to allow access with a socket to the switches. It was a matter of curving them a bit to give it enough clearance...a little bending, but not a biggie.

Now, I do not ever expect to take those out. I made sure I had German made switches and have the relay, which as I said previously, lasted 10 years in my other car without issue.

D.