6 replies to this topic

[Rob Gendreau]

I've got no brake lights on my 93.

Checked bulbs; OK. The green wire to the trunk light was severed, but I don't think that matters. Fuse OK.

I put a meter on the brake light switch, and got no power at all. Not on the green with switch on, and not on the green/white at any time. From looking at some diagrams online, this circuit shares with horn and cruise control, neither of which are connected, so I can't test. The wiring is a a bit, er, idiosyncratic: previous owners did some stuff and it's awful hard to find anything in there.

Rather than messing about diagnosing, how 'bout I just find a decent 12v wire that's hot when ignition is on, fuse it, and run it to a splice into the green/white wire, which is always supposed to be hot? I think it pulls 27w max, so something off the cig lighter (which I also rewired, but use for powering the iPhone lap timer) should work, right?

Rob

[dstevens]

Not withstanding the fact race cars shouldn't have brake lights anyway, this could be symptomatic of a larger issue in the electrical system. Particularly since the first guys have been in there.

Looking at a 1.6 schematic the only things tapped on after the switch are the ABS control unit, a part of the ecu and the cruise control. It's right to the lamps from the switch, the outsides are 2 x 27 w and the deck lid shows an 18.4 w lamp. If you do decide to "cowboy" something up (as we say in our biz) it will need to be able to supply about 7 amps of current at 12vdc.

[Tom Hampton]

Rather than messing about diagnosing, how 'bout I just find a decent 12v wire that's hot when ignition is on, fuse it, and run it to a splice into the green/white wire, which is always supposed to be hot? I think it pulls 27w max, so something off the cig lighter (which I also rewired, but use for powering the iPhone lap timer) should work, right?

Rob

Nothing good comes of skipping the diagnosis bit. It's a race car, slow down, figure it out, and fix it right.

If the wiring is as much of a mess as you say, maybe you just need to get a new harness. You might find more surprises.

[Rob Gendreau]

Nothing good comes of skipping the diagnosis bit. It's a race car, slow down, figure it out, and fix it right.

If the wiring is as much of a mess as you say, maybe you just need to get a new harness. You might find more surprises.

Ideally, I would. But it's way more time/expense than I want to do. All the other stuff on this circuit is disabled for racing. I prefer to have something simple and reliable. Short of tuning the lamps off and on manually, a 12v connection with fuse, bulb and one switch is about as simple as it gets. I suspect that's why Mazda set it up this way, relatively simple for a street car.

Nevertheless I'll look at the other parts of the circuit; I suspect that in disabling that maybe they screwed something up.

Oh, they required the brake lights at the NASA HPDE I was doing.

Rob

[davew]

Tom is right. A quick fix will get you through the weekend, but should not be considered perminent. One funky circuit usually means problems down the road. Many used parts suppliers have 1.6 harnesses pretty cheap. It is not difficult, but is time consuming to change.

I just finished a repair job that required both the main interior harness and a dash harness. Original problems were. the battery was overcharging, battery light on, check engine lite on, ecu would not talk to scan tool. Once we "cowboyed" enough things to comunicate with the scan tool we found 4 codes. And the car ran with the main injector fuse removed !!!!!

Most of the problems where caused by additions to the wiring for data and a very poorly designed kill switch wiring.

If the harness is hacked up, just change it out. You will be time and money ahead in the long run

Dave

[Tom Hampton]

Rob-

*IF* I were going to cowboy something up, I would bypass and disconnect the original wiring completely. I would not SPLICE INTO the existing wiring. There might be a reason that there is no power to the brake circuit...a bad one. Running power to the existing wiring might lead you down the path of insanity (you step on the brakes and the wipers start moving...or the washer fluid starts pumping...or it dead shorts 12V to ground...or something more subtle and insideous).

I would run a brand new, 18 (or 16) AWG, 10 Amp fused, +12V wire to the brake switch, and brand new wire from the brake switch to the trunk. I would cut, cap, and stow all bypassed, original wires associated with the circuit. AT A MINIMUM, I would make sure you can visually inspect EVERY INCH of any wires you elect to retain. If you can't see it, you should assume its bad...and bypass it. Be sure to label everything on both ends, and cover the label with something water proof.

Preferably, you would ALSO get a multimeter on both ends of the wire and check for continuity, and resistance: both along the wire and to chassis-ground. With both ends of the wire disconnected the wire resistance should be 0.100 ohms (really even less....but, you're limited by the meter and contacts...less than 1 ohm is good), resistance to ground should be OL or 10+ mega-ohms.

Neither is really sifficient by itself. A wire can have a chafe that makes intermittent contact with the chassis (passes the mutimeter test)...or there can be an chafe that isn't currently touching a body part. Even with both visual and electrical inspection, there are still problems that can only show up under vibration or G-loading. Also look for discoloring on the terminals or any exposed copper: blue, green, and black are all bad signs. Cue tips and rubbing alcohol can be used to clean any general grunge.

These inspections should include the brake switch itself (both open and closed), the brake bulbs and associated wires. I'd probably also hook up a test 10A FUSED +12V wire to the brake lights to be sure they light up, and don't blow the fuse.

I would NEVER hook up power to a circuit of unknown or suspect connectivity or status.

Then I would plan on a harness replacement at the earliest opportunity.

[Johnny D]

Is this the car?

http://mazdaracers.c...tem&item_id=311

No mention of this problem.
J~