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Brake Light Switch Failure

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gmlaverda

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I have a 100-4 with a low mileage restoration. Recently upon checking the lights for function I noticed I had no brake lights. I traced the problem to the brake light switch in the hydraulic brake system. The wires terminated at the switch were corroded as was portions of the switch. When I say corroded it has the appearance of electrolysis I think, a white powdery coating on the wires and switch. There is zero rust on the chassis.

I cleaned this white powdery substance from the switch, cleaned and restripped the wires, reterminated them and all was fine for a while. I've added a couple hundred miles since then and the condition has come back along with the lights failing again.

Any ideas what is happening here?
 
If your brake switch is located on the front crossmember perhaps there is some leakage from the radiator getting on it and causing the corrosion.
 
These switches are a common failure point. I believe they are simply a rubber(?) diaphragm with a metal strip that flexes against a couple contacts when the brakes are pressed, and the diaphragm--like many diaphragms--can fail. The corrosion may well be from leaking brake fluid. I've replaced several over the years, though they usually fail by not working.

Side note: This issue isn't limited to Healeys. A few years ago there were some stories of Ford Rangers--I have a '96--spontaneously catching fire (I think some garages were destroyed). The truck, and likely many other makes/models, had a similar type of switch that sensed the pressure when brakes were applied and disconnected the cruise control.
 
Those switches are usually brass, I believe. Electrolysis is probably the culprit, as you thought. Stainless forces metals like copper and aluminum to sacrifice themselves. I saw a classic Mini, where someone had put stainless bolts to secure the aluminum clutch master cylinder. That was enough to turn the aluminum to a nasty, fuzzy green color. I now am careful where I put stainless hardware. Zinc coated steel is the best choice versus stainless. The electric current helps speed up the electrolysis.
 
Though teflon tape is not necessary to make a good seal between the brake line nut and the switch body it might serve to lessen contact/conductivity assuming the nut lands do not cut through it entirely.

The diaphragms in these pressure switches often harden as they age, usually requiring increased pedal pressure in order for contact to be made. Usually people test their brake lights by stomping hard on the pedal and when the lights come on all is assumed to be good. However, in normal driving we seldom stomp on the brakes and it is better to test the circuit by having someone observe when the lights come on as we modulate pressure.
 
If it screws into the master cylimder, my Dad used a 1954 Chevy switch. Just happened to screw in with no problem on a 57 Jag 140.
 
Bristol401 said:
Those switches are usually brass, I believe. Electrolysis is probably the culprit, as you thought. Stainless forces metals like copper and aluminum to sacrifice themselves. I saw a classic Mini, where someone had put stainless bolts to secure the aluminum clutch master cylinder. That was enough to turn the aluminum to a nasty, fuzzy green color. I now am careful where I put stainless hardware. Zinc coated steel is the best choice versus stainless. The electric current helps speed up the electrolysis.
Click to expand...

Interesting point. I wonder if same occurs when SS lines are screwed-into brake cylinders? I think, not sure at all, the male portion of the flare is made of steel, SS maybe? Does anybody use SS flare nuts (don't think I've ever seen them).
 
This chart is very helpful for me… had one like it in my college Metallurgy class years ago. One thing though.. the chart is changed by the amount of each metal. A large piece of aluminum is not affected much by a small number of stainless bolts. Also changes if the pieces are stuck out near ocean fog where I live. Salty Fog sucks.
 

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The plot thickens. After the question about stainless pipes I crawled under the car and checked the brake cylinders. All four cylinders had these deposits or coatings. The front cylinders were worse than the rear. I've attached a photo of the right front cylinder. I also appear to have some minor deposits on a brake pipe strap in the engine compartment.
I'm pretty concerned not knowing how aggressive this condition is and feeling that the fix is pretty ugly. This car has a little over 1000 miles on a ground up restoration.
 

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Wow. I've never seen anything like that--the 'goldish' color especially--and I've done a bit of work on several older cars and tractors.
 
gmlaverda said:
The plot thickens. After the question about stainless pipes I crawled under the car and checked the brake cylinders. All four cylinders had these deposits or coatings. The front cylinders were worse than the rear. I've attached a photo of the right front cylinder. I also appear to have some minor deposits on a brake pipe strap in the engine compartment.

I'm pretty concerned not knowing how aggressive this condition is and feeling that the fix is pretty ugly. This car has a little over 1000 miles on a ground up restoration.
Click to expand...

Those deposits look like they're on the surface only - at least for now - and so I wonder if it would be an adequate solution to spend a few minutes with a toothbrush-sized wire brush, followed by a light coating of something like this stuff:

IMG_6330.jpg
 
Thanks for the suggestion. It may be a decent short term fix. My concern is how aggressive this electrolysis appears to be, evidenced by a very short lived the brake light switch, assuming that did not fail due to some other cause.
 
I have no other guess/hypothesis, but this doesn't look like electrolysis/galvanic corrosion to me. In my experience, it occurs at the point of contact of the dissimilar metals; e.g. at the Al shroud/steel wings flange. If this was common, anyone with SS brake lines would have it, and this is the first I've heard of any issue with SS (besides a bit more difficulty bending it).
 
From my experience in boats, stainless can wreck havoc on aluminum. And the electralisis between the aluminum, steel, copper and stainless in Land Robers. Lots of gaskets and copper anti-seize on bolts and seams.
 
Perhaps there is some electrical leakage onto/into the brake lines that is accentuating the electrochemical reaction between the lines/switch and the frame. It might be interesting to temporarily remove the brake switch fasteners, isolate it from the frame, put a volt meter between the two with ignition both off and on and with the brakes activated.
 
Interesting point Michael, one connector on the brake light switch has 12V all the time when the key is on. If the rubber diaphragm in the switch has failed and leaked brake fluid into the area with the contacts, then a small current could be passing through the fluid into the metal body of the switch. But the OP has stated that after the wires and connectors were cleaned it worked for awhile then failed again. If the rubber diaphragm had failed I don't think the brake lights would work.
As a side note the replacement brake light switches aren't very good and fail quite often so I added a relay a few inches away from the brake light switch to pass the high current through. The contacts in the switch only pass a very small current now.
There are ten pages here discussing the switches with pics of failed ones.
MGA Guru Brake Light Switch Info
 
Thanks gentleman for the ideas. I'll be out of town for several days and when I return home I will dig a little deeper. I have ordered a new brake light switch so I may dissect the old one to learn a bit more. Expect an update.
 
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