What the brake light switch does and where it sits
The brake light switch on your 1990 Dodge Ram B350 is a straightforward electrical device mounted near the brake pedal under the dashboard. When you press the brake pedal, the switch closes an electrical circuit that tells your brake lights to turn on. When you release the pedal, the switch opens and the lights turn off.
On the B350, this switch is located on the brake pedal bracket itself — you'll find it by looking up under the steering column where the pedal connects. It's a small cylindrical or rectangular component with one or two wires running to it. The switch is held in place by a clip or bracket and can usually be removed by hand or with a socket wrench, depending on how it's mounted on your particular truck.
A faulty brake light switch is one of the most common reasons brake lights fail on older Dodge trucks. Because the switch is mechanical and gets used thousands of times, the internal contacts can wear out, corrode, or get stuck over time.
Key Takeaways
- The brake light switch sits on the brake pedal bracket under the dashboard and closes an electrical circuit when you press the pedal.
- A bad switch will cause your brake lights to stay on, stay off, or flicker — even if your bulbs and wiring are fine.
- Testing the switch with a multimeter takes about five minutes and tells you whether it's the problem before you buy a replacement.
- Replacement switches for the 1990 B350 cost between $15 and $40 and can be swapped out in under 30 minutes without special tools.
- If your brake lights work but the switch feels loose or the pedal feels different, the bracket itself may be bent and need adjustment.
Signs your brake light switch is failing
Brake lights that don't work at all are the most obvious sign, but a failing switch can also cause lights that stay on constantly, flicker when you touch the pedal, or work only sometimes. You might notice the lights come on when you're driving over bumps, or they stay lit even when you're not braking.
Some owners report that the brake lights work fine but the pedal feels mushy, loose, or sits lower than it used to. This usually means the switch bracket is bent or the switch itself is stuck in the closed position and not releasing properly. A stuck switch can also trigger a check engine light on newer vehicles, though the 1990 B350 doesn't have that system.
If your brake lights work perfectly but you see brake fluid leaking from under the dashboard, the problem is likely the brake master cylinder, not the switch. The switch and master cylinder are separate components mounted near each other, and it's straightforward to confuse them.
How to test the switch before replacing it
You can test the brake light switch with a multimeter set to the continuity or ohms setting. Unplug the wires from the switch (note which wire goes where), then touch the multimeter probes to the two terminals on the switch itself. When the switch is unplugged and at rest, it should show no continuity (infinite resistance). When you press the brake pedal by hand, the switch should close and show continuity (zero or near-zero resistance).
If the switch shows continuity when it's not being pressed, or no continuity when you press the pedal, it's bad and needs replacement. If the test shows the switch is working correctly but your brake lights still don't work, the problem is in the wiring, bulbs, or fuse — not the switch.
If you don't have a multimeter, you can do a simpler test: turn on the ignition, unplug the switch, and touch the two wires together. If your brake lights turn on, the switch is bad. If they stay off, the problem is elsewhere in the circuit.
Choosing and installing a replacement switch
Replacement brake light switches for the 1990 B350 are sold at most auto parts stores under the Dodge or Mopar brand, or as generic aftermarket parts. The part number for the OEM switch is Mopar 4874371, though compatible switches from other manufacturers will work as long as they're designed for a 1990 Dodge Ram. Ask the parts counter to confirm the switch fits your specific model year and engine size.
Installation takes about 20 minutes. Disconnect the negative battery terminal first, then crawl under the steering column and locate the switch on the brake pedal bracket. Unplug the wires, remove the clip or bolt holding the switch in place, and slide the old switch out. Slide the new switch in, find it with the clip or bolt, and plug the wires back in. Reconnect the battery and test the brake lights.
Most switches come with a small rubber boot or seal that fits over the pedal rod. Make sure this is in place before you install the switch, or moisture can get inside and cause corrosion. If the old switch's boot is damaged, you can often reuse it on the new switch.
Common installation mistakes and how to avoid them
The most common mistake is installing the switch upside down or backwards. The switch has a plunger that must face the brake pedal rod — if you install it backwards, the plunger won't make contact when you press the pedal and the lights won't work. Check the old switch before you remove it to see which way the plunger points, then install the new one the same way.
Another mistake is over-tightening the mounting bolt. The switch body is plastic on many aftermarket units, and tightening too hard can crack it. Hand-tighten the bolt until it's snug, then stop — you don't need to use a wrench with full force.
If the brake lights still don't work after you install a new switch, check that the wires are fully plugged in and that neither wire is corroded or broken. Corrosion on the wire terminals is common on older trucks. If you see green or white buildup on the terminals, disconnect them, clean them with a wire brush or fine sandpaper, and reconnect them.
When the switch works but the pedal feels wrong
If your brake lights turn on and off correctly but the brake pedal feels loose, spongy, or sits lower than it should, the problem is usually not the switch itself but the bracket it's mounted on. The bracket can bend if the pedal is pushed too hard or if the truck has been in an accident. A bent bracket can also cause the switch plunger to not make full contact, leading to flickering lights.
To check the bracket, look at it from the side while someone else presses the brake pedal. The pedal should move straight back without tilting or binding. If it tilts or moves unevenly, the bracket is bent and should be straightened or replaced. This is a more involved repair than replacing the switch and may require removing the entire pedal assembly.
If the pedal feels spongy but the bracket looks straight, the problem is likely air in the brake lines or a failing master cylinder — not the switch. Have the brake system inspected by a mechanic before you assume the switch is the cause.
Wiring and electrical considerations for the B350
The 1990 Dodge Ram B350 uses a straightforward two-wire brake light circuit. One wire carries power from the fuse box (usually a 15-amp fuse labeled "STOP" or "BRAKE"), and the other wire grounds to the truck's chassis. When the switch closes, it completes the circuit and power flows to the brake lights.
If you're replacing the switch and the lights still don't work, check the fuse first. A blown fuse is more common than a bad switch. The fuse box is usually under the dashboard on the driver's side or under the hood. Look for a fuse labeled "STOP" or "BRAKE" and replace it with one of the same amperage if it's blown.
If the fuse is good and the lights still don't work, trace the wires from the switch to the rear of the truck to look for cuts, corrosion, or loose connections. Mice and rodents often chew through brake light wiring on older trucks stored outside. A broken wire will need to be spliced or replaced, which is beyond the scope of a straightforward switch replacement.
Frequently Asked Questions
Can I drive my B350 if the brake lights don't work?
No. Brake lights are required by law in all states, and driving without them is illegal. More importantly, other drivers won't know you're braking, which creates a serious safety hazard. Fix the brake light switch or have the system inspected before you drive the truck on public roads.
Will a bad brake light switch affect my brakes themselves?
No. The brake light switch only controls the lights — it has nothing to do with the actual braking system. If your brakes feel soft, spongy, or don't stop the truck, the problem is in the hydraulic system (master cylinder, lines, or pads), not the switch.
Do I need to bleed the brakes after replacing the switch?
No. The switch is an electrical component that sits outside the hydraulic brake system. Replacing it does not disturb the brake fluid or air in the lines, so bleeding is not necessary.
What if the new switch doesn't fit the bracket?
This is rare but can happen if you buy a switch designed for a different model year or engine. Return it to the parts store and ask for a switch confirmed to fit the 1990 B350. Bring your truck's VIN or a photo of the old switch to make sure you get the right part.
How long does a brake light switch usually last?
On a 1990 truck, the original switch may have already failed or be close to failing. Replacement switches typically last 10 to 15 years depending on how often you brake and whether the truck is stored in a dry place. Trucks used in wet or salty climates tend to have switches fail sooner due to corrosion.