The MGA With An Attitude
BRAKE LIGHT SWITCHES Fail with Burned Contacts -- FT-071

brake switch For more information on brake light switches, see:
ET-119A - BRAKE LIGHT SWITCHS, Good Ones or Bad Ones
ET-119X - BRAKE LIGHT SWITCH, Construction and Failure
ET-119X2 - BRAKE LIGHT SWITCH Failure, Borg Warner
ET-119X3 - BRAKE LIGHT SWITCH Failure, Intermotor

As this is not a snap action switch, the contact points close and open slowly. This allows a weak spark to jump the gap during actuation, which eventually has a burning effect on the contacts. As the contacts get dirty the contact resistance rises. The contacts then generate heat with the current. With time the resistance goes higher, and the heat will be greater. Eventually contact resistance becomes unacceptably high with unreliable contact. Then you have to stand hard on the brake pedal before the switch will make adequate electrical contact. When the pressure required is too high, there will be no contact, and the brake lights do not work. There is no wiping action on these contacts, so the contacts are not self cleaning. The most common problem with switches that fail is poor material for the contacts. Plating the contacts with gold, silver, or even nickle might stop the corrosion and burning. Bottom line is, many of these switch are unreliable due to cost cutting pennies on the quality of the internal electrical contacts.

This Borg Warner S550 brake light switch (from Advance Auto Parts) is dead, no brake lights with any amount of pedal pressure, slightly less than two months 5,000 miles.

We opened the failed Borg Warner switch with a grinder to disclose the failure mode and the design-manufacturing deficiency. The contact plate is steel with a thin copper (or maybe cadmium) flash plating. It didn't take long to burn away the flash plating, after which the steel plate will corrode rapidly. Lots of driving in 60 days, 5000 miles, may have done 1000 to 3000 operation cycles on this switch. Since my trailer lights are LED's, total current for this switch is just 4-amps. A copper contact disc would be perhaps $0.02 worth of material. I can't imagine how much cost they thought they were saving by using the plated steel disc.

Addendum November 22, 2014:
Failed another switch today. This time Standard Motor Products SLS27T (peg post terminals) from Advanced Auto. Similar to the last one, eight weeks and about 5000 miles. This one had a copper contact disc, but burned off thin copper plating from contact points on the steel terminal posts.

Addendum February 13, 2015:
Another Borg Warner switch, BWD S194 (peg post terminals). This one made it a little longer, 11-weeks 8400-miles. Again burned off thin copper plating from contact points on the steel terminal posts. Photo after cleaning with vinegar and salt.

For a large cross reference list of interchangeable brake switches see:
ET-119A - BRAKE LIGHT SWITCHS, Good Ones or Bad Ones
Hydraulic switch failure has been epidemic in recent years. I will list any and all bad switches that are reported to me, in the hope that we might eventually find a source for a good switch.

Addendum Apri 1, 2015:
This time the NAPA Echlin SL134 (Mexico) failed in 7-weeks 6880-miles. The common link for all the failed switches (5 failed in 10 months, 5000 miles average) is "Made in Mexico" (and I would lay odds they all came from the same factory).

Addendum December 3, 2015:
We may have a winner. Duralast RB401 (Made in Spain) purchased at Autozone. Five months and nearly 15,000 miles, and it is still working.

3 JUL 2015 - 303,538-miles - New switch Autozone/Duralast RB401 (Spain)
3 DEC 2015 - 318,362-miles - And it is still working.
8 NOV 2016 - 349,474-miles - And it is still working.

Addendum November 10, 2016:
On 11/10/2016, Darrell Martin wrote:
"The attached photo is of an ISSPRO R4006-4 switch I recently used on a power assisted system in our BGT. I did not pull it apart, rather it "blew its top" with the plastic/resin section totally detaching itself from the metal body. The engine bay then received a liberal coating of brake fluid. Despite my best efforts I cannot get the two sections back together (just to see how tightly it was manufactured)".

This was a mechanical failure, not electrical. Perhaps we should not blame the manufacturer for this one. It is designed for actuation at 4-psi. The brake hydraulics develope about 500-psi pressure, and the switch should actuate at about 50 psi (25-psi minimum switch point). Maybe this switch was not intended for use with 500 psi pressure.

Thank you for your comments -- Send e-mail to <Barney Gaylord>
© 2014-2017 Barney Gaylord -- Copyright and reprint information