📋 Quick Facts
Time
10 minutes
Difficulty
Easy
Tools
2 tools
Cost to DIY
$15-30
A bad brake light switch causes brake lights stuck on, brake lights that do not come on, cruise control that will not engage, no-shift from Park, and a check engine light. A 10-minute multimeter test gives a clear pass/fail.
🛠 What You'll Need
- Digital multimeter (shop a digital multimeter on Amazon)
- Test light (shop test lights on Amazon)
- Safety glasses (shop safety glasses on Amazon)
Product links above are Amazon affiliate links. AmpAuto earns a small commission at no extra cost to you.
⚠ When NOT to DIY thisDo not adjust a brake light switch with the brake pedal pressed. The switch can be ratcheted out of alignment and cause lights stuck on the moment you release the pedal. Always adjust with the pedal fully up.
🎯 Expected Readings (Pass/Fail Reference)
| Switch continuity, pedal RELEASED | Open circuit (OL) on output pin |
| Switch continuity, pedal PRESSED | Under 0.5 ohms across input/output |
| Battery voltage at switch input pin | 12.4 - 12.7 V DC, always (constant power) |
| Output to brake lights, pedal PRESSED | 12.4 - 12.7 V DC |
| Output to brake lights, pedal RELEASED | 0 V |
| Stored DTCs | P0504 (brake switch correlation), P0703 (brake switch input) |
Numbers are typical. Always cross-check against your factory service manual for the exact spec.
📝 Step-by-Step Test Procedure
- Locate the switchMounted to the brake pedal bracket up under the dash. A small plastic body with a plunger that presses against the pedal arm. Usually 2-pin (basic) or 4-pin (with cruise control / shift interlock).
- Look at the symptom firstBrake lights stuck on = switch is stuck closed. Brake lights never come on = switch stuck open or no power. Both reds out = bulbs, fuse, or wiring (rare for the switch).
- Pull the brake light fuse and checkA blown brake light fuse mimics a bad switch. Check the fuse before disassembly.
- Unplug the switchPress the locking tab and pull the connector off the switch.
- Test for power at the connectorSet multimeter to DC volts. Probe the input pin (constant 12V side). Should read 12.4-12.7 V at all times, key in or out.
- Test switch continuity with the pedal releasedSet multimeter to continuity (ohms). Touch probes to the switch terminals. With the pedal up, reading should be OL (open). If it reads near 0 ohms, the switch is stuck closed - lights on all the time.
- Test switch continuity with the pedal pressedHave a helper press the brake pedal. Continuity should now read under 0.5 ohms. No change = switch stuck open.
- Adjust the switch (older mechanical types)On older GM, Ford, and Dodge vehicles, the switch has a threaded body that can be turned to adjust the plunger depth. Misadjustment after pedal work is a common cause of stuck-on lights.
- Check the brake pedal striker padMany cars have a small foam or rubber pad on the pedal arm that the switch plunger rests against. When that pad disintegrates, the switch falls forward and the brake lights stick on. Common on Honda, Toyota, and Hyundai.
- Reconnect and confirm with a test lightPlug the connector back in. Probe the switch output terminal with a test light. Light should be off pedal-up, on pedal-down.
✅ Pass / Fail Criteria
✅ PASS
Constant power at input pin, open circuit with pedal released, under 0.5 ohms with pedal pressed, brake lights work normally, no P0504 or P0703 codes, striker pad intact.
❌ FAIL
No power at input pin (blown fuse or broken wire), stuck-closed switch (lights always on), stuck-open switch (lights never on), or missing striker pad on the pedal arm.
🔧 If It Fails - What To Do Next
Replace the switch. Part is typically $10-$25, labor 10-15 minutes. On Hondas, also replace the brake pedal striker pad ($2). See our guides: P0504 brake switch correlation and Brake lights stuck on.
🔗 Related Guides
❓ Frequently Asked Questions
What are the symptoms of a bad brake light switch?
Brake lights stuck on, brake lights not coming on, cruise control will not set, shifter stuck in Park, or check engine light with P0504.
Can a brake light switch cause a no-start?
On some modern vehicles, yes. Push-button start systems require the brake switch to confirm pedal-press before cranking. A failed switch can prevent start.
How much does a brake light switch cost?
$10-$25 for the switch, 10-15 minutes labor. Add $2 for a striker pad on Hondas and Toyotas.
Why are my brake lights stuck on?
90% of the time it is a failed striker pad (the foam pad on the pedal arm) or a stuck-closed switch. Reach under the dash and look for crumbs of foam on the carpet under the pedal.
Will a bad brake switch fail an inspection?
Yes. Brake lights are required and the cruise/shift interlock is a safety system. Most states fail any vehicle with non-working brake lights.
Can I drive with a bad brake light switch?
Briefly, to a shop. You will lose brake lights (rear-end collision risk) and possibly cruise control and shifter operation. Fix immediately. See our can-I-drive guide for details.