(BRAKES) Troubleshooting Brake Lites...

Old 03-23-04, 09:30 PM
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Cool (BRAKES) Troubleshooting Brake Lites...

Brake lights inop can be a royal pain, particularly when it goes beyond "blown fuse". This isn't intended to be the definitive, all-encompassing, cure-all brake light troubleshooting guide, but it is meant to help those with, shall we say, less than professional troubleshooting skills to pinpoint problems with their brake lights. First, here are some specific troubleshooting steps common to resolving any problem:

1. Identify the problem. In this case: "My brake lights don't work." pretty much identifies it.
2. Investigate possible causes. Do this by learning as much about the system as you can from service manuals, friends, "RX7 Forums", etc. Try to understand how the system works. Possible causes begin to emerge in your mind.
3. Determine the cause. You do this by eliminating everything that's not causing the problem and isolating the thing that is. Start with the most simple (is a fuse blown?) and progress to the more complex (is a wire broken?).
4. Repair the problem. You can do this by replacing or rebuilding the item.
Now, on to the "My brake lights don't work" problem... If you've done your homework, you'll know there are several things in the system that could cause the problem. In isolating or determining the cause, remember "KISS" (Keep it Simple, Stupid). Start with the simplest and/or easiest things to check. The most obvious cause and simplest to check for would be a blown fuse...

You can check the fuse by simply honking your horn. It uses the same fuse. If the horn works, the fuse is okay.
The next most obvious thing in the system to check would be the "Brake Light Switch", however the simplest and easiest thing to check next would be the light bulbs themselves. Although rare (happened to me only once) they have been known to all blow at once...

If the bulbs are okay, while you're back there you might want to confirm that you are or are not getting power to the lights. The wire to check is the green one with brown rings and no stripe. If you have power to this wire and your bulbs are good but don't light, you probably have a bad ground. Test this by directly grounding the bulb socket side against the frame while someone steps on the brakes. Seems to me, though, that if your ground was bad, you'd have other than just your brake lights inop since all the taillights use the same ground wire.
Now it's time to check the brake light switch. I check the bulbs and wiring in the tail first just because it's easier. Of course, if you're only 20 years old and built like a rubber bean stock, checking the brake lite switch is just as easy. If, however, you're like me and older than Moses - it's not fun turning upside-down and inserting the top half of your body under the steering wheel, with one arm at an abnormal angle, and your head wedged between the pedals!...

The brake lite switch for an RX with cruise control has two plugs going to it while non-cruise equipped cars have a switch with just one plug. Disconnect the white plug that has one green wire with brown rings (hot wire) and one white wire with red/brown rings from the brake light switch and jump the connectors...

If your brake lights come on, the brake light switch is bad. You can get a new one for $7-$15 from AutoZone, Advance Auto Parts, Victoria British, or Mazdatrix.
If your lights do not come on, things begin to get a little more complex. First check that you have power to the green with brown rings wire. If you don't, you may have to replace the wire from the fuse box to the plug (or run a new one). If you do have power, give the "Brake Light Check Relay" a nice "technical tap" (whack it with a wrench!). If your lights suddenly start working (as mine did), you had a stuck relay. If not, you may wish to bypass the relay with a jumper as we did with the brake light switch (same wire colors), but since I didn't actually test that - I'm not gonna tell you how 'cause I don't want you to burn your car down!
If you still don't have lights, the next thing to check is the connector under the driver's side boot. Leave the jumper wire installed on the brake light switch and...

check for power to the green wire w/brown rings on both sides of the connector to make sure the connecter terminals are okay. If you have power to both sides, and your lights don't work, the most likely culprit is a broken wire from the connector to the taillight area. If you have power on the front side of the connector but none on the back side, you have a bad terminal in the connector. Before we go to the next step, go ahead and check for power to the white wire with red/brown rings going into the cruise control module (if you have one). Should have power there with the jumper wire on the brake light switch plug or when the brakes are applied.

Now, if you had no power at all on the brake light wire at the connector - you may have a break in the wire between the switch and the connector -or- you may have a bad or stuck "Brake Light Check Relay". As I mentioned you can bypass the relay -or- in both cases, a broken wire or a bad relay, you can make an emergency temp repair (while under the boot) by jumping a wire between the white wire with red/brown rings going into the cruise control module and the green wire with brown rings going into the main connector. You should get brake light right away. Remove the jumper from the brake light switch plug and reconnect the plug to the switch. You should have brake lights whenever you step on the brake pedal. If you don't have cruise, you're SOL on the qwik fix, you'll have to run a wire all the way from the "white" wire on the brake light switch to the green wire at the connector. But remember, these are just a temporary fix until you replace the relay or broken wire and to get you passed the safety check if need be. I've looked and I haven't found a relay yet, but I haven't checked with Mazda either. Why do I think they'll want an arm and a leg for one?

I hope this post makes sense to you. I understand it.

Last edited by zookeeper; 03-23-04 at 09:42 PM.
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