There has been lots of discussion about cheap brake light pressure switches that fail early in life, so there must be a lot of them on the market. There is also some discussion about how to install a relay to reduce the electrical load on the pressure switch in an attempt to make a garbage switch last longer. I would never recommend the relay installation as it unnecessarily adds complexity and an increased probability of some of the added parts failing. more work to install, and more future maintenance problems. For those inclined to be curious, click the off-site link to the Brake Light Relay. Another approach is to install a mechanical switch on the brake pedal. I don't recommend that either for the same reasons, non-standard parts, and bother to install.

The correct answer is to buy a good pressure switch that will not fail. The trick is how to figure out which ones are good or bad before you buy one. It is likely that they all work when new, and there is no visual clue for reliability when new. If you were so inclined you might run a test for required switching pressure and contact resistance. The thing should switch on with about 20 psi pressure, and electrical resistance should ALWAYS be less than 1/4-ohm (250-milli-ohm max). A switch might meet these requirements when new and fail prematurely anyway, so these test may not be much benefit in evaluating a new switch (unless it is actually bad when new). The bad switches fail due to very cheap electrical contacts inside that may burn and increase resistance with normal use. As far as I can tell, no pressure switch has ever failed due to use of silicone brake fluid, so you may ignore any mention of that issue.

The objective here is to identify bad switches by reporting field failures. It is not easy to get people to report a failed part when a replacement costs less than $10. The proper action for a switch that fails early is to report it to the supplier immediately. If you can take enough time to bitch about it on a web forum, then you should also name the supplier, the suppliers part number, and anything else you can tell to identify the part. If you will do that, then I will be happy to list it as a faulty part, which will in turn give the supplier a chance to get the problem fixed (and for buyers to avoid it until it is fixed). So far I hear lots of complaining but precious few reports with useful information.

The brake light pressure switch is otherwise a generic device, widely available. The threaded end needs to be 1/8-NPT (tapered pipe thread, 27 threads per inch). Original terminal style (for MGA) is set screw post, but you can use a switch with push-on terminals by installing Lucar connectors on the harness wires. I will list here as many cross reference numbers as I can find, or as many as people will report. All switches will be assumed to be good until someone reports failure of a switch with a specific manufacturer and part number. If you have a failed switch it would be good if you can cut it open and get a close up picture of the failed contacts. It would also be good if you can persure test a switch, either new or failed, to determine the required pressure for switching. See follow-up reports good or bad on the following page.

3H1894 - (this style screw posts unless otherwise specified)

SL134 NAPA/Echlin Peg terminals

SL134SN NAPA/MPE Spade terminals

SW-32 - Ron Francis T-top terminals

 

3H1894 - Switch - stop lamp (original BMC part number) 3H1894 - kipmotor.com (Metrololitan parts) 3H1894 - MGOC_Spares 141-700 - LBCarCo 141-700 - Moss Motors 1S10683 - Rock Auto (Airtex/Wells) - {SW8048} 201-0130 - Beck/Arnley - spade terminals - (17M8) 31082 - Lucas (34445; 34542; 34765) 34542 - St George Ltd - (141-700; 201-0130; 31802; 34765; 542-110; C16062; SMB423; SPB400) 51600 - Intermotor 542-110 - LBCarCo - spade terminal 542-110 - Moss Motors - spade terminal 8-341 - Victoria British Ltd C16062 - MGOC - spade terminals HL2 - MNW Isetta 300 - (Lucas 31082) IM5162 - EnglishParts.com - (141-700; 293699; 2A5304; 3H1894; 62057; BMK1278; C16062A; IM5162; SC332; SC333) SL134 - NAPA/Echlin ECH SL134 - peg terminals SL134SB - NAPA/MPE MPE SL134SB - (Mileage Plus Electrical) - peg terminals SLS273 - Rock Auto (Standard Motor Products, made in USA) - {31440, 34765, E852} SMP-SLS273 - Summit Racing (Standard Motor Products, made in USA) SPB400 - Lucas (31082) SMB423 - Lucas - with lucar terminals SW32 - Ron Francis Wiring (non-standard terminals, but special connector included) SW8048 - AutoZone

Also used on: AC Cobra 64-65 Alfa Romeo 1750 Berlina GTV Spider Veloce 68 GT Junior 1300 66-68 Sprint 65 Aston Martin DB2-4 57 Aston Martin DB4 58 Aston Martin DBD 58 Austin 1100, 1300 +GT 69-74 1300 GT 70-74 A60 Cambridge 1600 66-69 Mini 59-69 Mini 850, 1000 64-73 Mini Clubman 1000 70-73 Mini Cooper 62-65 Mini Cooper S Vanden Plas 1300 Princess 67-74 Austin Healey Sprite MKI 62-66 100, 3000 BN1-BJ8 53-67 BMW Isetta 300 54-60 Borgward Lloyd Alexander 57-60 Daimler Limousine 69-92 Sovereign 2.8, 4.2 69-71 Fiat 238 69-83 Ford Anglia 63-67 Escort 1100,1300 68-70 Escort Twin Cam 68-71 Hillman Hunter 66-70 Husky 56-66 Minx 50-67 Jaguar 240, 340 67 420, 420G 66-70 Mk2, MkVII, VIII, IX 63-66 Mk3.8S E type 61-71 E type DH,FH Cp 4.2 69-72 XJ6/XJ 2.8, 4.2 68-71 XK120, XK140, XK150 55-56 Land Rover series IIA 62-69 LTI Carbodies FL2 Hire Car 2.25D 72-77 FX4 Taxi 2.25D 72-85

Maserati Bora 4700 70-78 Maserati Bora 4900 78-82 Maserati Khamsin 72-82 Maserati Merak SS 72-83 MG 1100 63-67 1300 68-71 MGA (all) 55-62 MGB 62-67 MGB GT Roadster 63-74 MGC GT Roadster 68-69 Midget 61-66 TC, TD, TF 45-55 Morgan Four Four 1600 82-85 Morgan Plus Eight 3.5 68-74 Morris 1100, 1300, GT 69-73 Mini 59-69 Minor 1000 63-67 Oxford 1600 67-71 Traveller 69-73 Nash Metropolitan (all) Rover 2000 63-72 RTI KC Walk-thru trucks 70-78 PB 1500, 2000, 2500 Spacevan Diesel 69-76 Singer Gazelle 57-58 Sunbeam Alpine 63-67 Arrow 67-69 Rapier 60-67 Tiger 64-67 Triumph 2000 66-68 GT6 68-70 Herald 59-67 Mayflower 50-53 Renown 50-52 Spitfire 62-67 TR2, 2A 54-55 TR3 to TS60000 55-62 R4, 4A 62-67 TR250 68 TR6 69-70 Volvo 544 57-61 Volvo 122 62-68 Vauxhall Victor 59-62 Wolseley 1100 68 1300 68-71 1500 58-64 16/60 69-70 Hornet 63-69