Car Electronics and Lights
Headlights Tail and Brake Lights
Dashboard Lights and Gauges

What can you do if the tail lights and dash lights are not working but the fuses are all good?


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2015-12-16 02:20:17
2015-12-16 02:20:17

This can be used for either the back-up lights or the brake lights.

There are a couple of ways to track this down. Of course, make sure your fuse and bulbs are in good condition. Disconnect the wiring to the switch. Measure the feed wire and make sure you have 12 volts. Note: Make sure the key is turned to the RUN position so you have juice to the wire. If there is no voltage, trace the wire back to the fuse and find out why! If you have 12 volts, connect a jumper wire of the correct gauge to jumper the connector. If the lights come on, it looks like a bad switch.

Put the car in reverse and use an ohm meter to check the resistance in the switch. It should be minimal. If not, replace the switch.

If everything looks good back to the bulbs. Go to the next step.

Disconnect the two bulbs and, put the car in reverse to engage the lights. Note: Try not to do this with the car running. If you insist, have a buddy with a strong, steady foot and chock the tires. Someone needs to be in the back measuring the power!

Measure the voltage at the socket. It should be about 12 volts. If it isn't you need to trace the wires back to the switch. If you see 12 volts, install one of the bulbs and remeasure the voltage. It may be that when there is no load on the circuit, everything looks fine. When you put a load on the system and the voltage drops, you have have a bad connection somewhere. Check your ground connections on the lights and check the connector at the switch.

2001 Mazda 626:

On a 2001 Mazda 626 (and I suspect many other), there is a relay in the fuse box under the hood. It is labelled the TNS relay. If your horn or headlights still work, swap the relays between one of them and the TNS relay. If, after making the swap, your lights now work and your horn does not, you have found the culprit. Unfortunately, neither Advance Auto, Autozone, O'Reilly, or Carquest stocks this relay. Some can order it - $19 and change at Carquest.


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