So, the #5 fuse that is for the brake lights, cruise control, horn, and shift lock keeps on blowing. It is meant to be a 15a fuse, there was a 20 in there when it blew from the PO, I tried a 25 and it blew when I put it in, then I tried putting in a 30 with the battery disconnected, and that blew right when the battery was connected again.

Earlier today I put in another 20 and it lasted for a 150mile drive, then just now it has started blowing the fuse the second I connect it.

Someone please tell me I am an idiot and that there is a simple fix for this, because I have a trackday tomorrow and really don't want to get **** for broken brake lights.

 

Um...you have a short in one of the lines...

Just a guess.

 

But, is there some kind of common short that causes this kind of thing?

 

well, if it's a dead short, which it sounds like it is, don't keep putting in bigger and bigger fuses!

 

Have you recently added a rollbar? When you cut the sheetmetal shelf, there's a possibility that it's rubbed some of the wires that pass through raw. Such was the case when I kept blowing the "INJ" fuse, turned out to be a short behind the driver's seat.

HTH

 

+1

Fuses are sized to be only slightly larger than the current the devices will draw under safe operation. If you have a fuse that blows, you should always find out the cause and not just pop another fuse in. If you keep up'ing the fuse size, you increase the amount of current that flows before the fuse pops. This means that if you put a 25A fuse in a 15A spot and it blows , then you are subjecting the devices to 66% more current than Mazda felt was safe.

 

Also, FWIW, if you're blowing the $2.99/pop fusible links one after the other, you can do like I did and install an in-line fuse holder on the spades the link attaches to so that you can blow through less expensive fuses while you troubleshoot.

 

I have had the rollbar in for a while, but I took off the metal luggage shelf panel and looked underneath, but didn't see any damage.

I've looked all over the damn car and can't seem to see any shorts. I have checked wiring form the cruise control, horn, horn buttons, brake lights, and under the luggage shelf and I have yet to find any shorted or crimped wires.

Does anyone have any info on the "shift lock"? I thought that was for auto cars, but maybe its something I just haven't heard of.

Any more ideas would kick ***.

 

Awesome thread title!

 

jesh you blow a lot of **** f50

 

I finished a day of tracking with no brake lights, and no black flags, and around a 2:14 at buttonwillow cw#13 so I'm golden.

But... naarleven, I'll blow one more **** if someone can tell me what this is. Although after looking all over the car, I think I'm going to need an ohmmeter and lots of time to diagnose this problem the old fashion way, because all of the easy to get to places seem to be fine.

 

What they said above. Don't put in a bigger fuse, it can send more current then what the wiring is rated for and if there is a short which is seems like you can cause a electrical fire and burn the wires up under the dash. I know this from experience. Find the problem fast and fix it. The short could be anything. One my older cars had an issue blowing fuses when I roll down the power windows and the issue was a bad wiper motor that had a short.

 

stock horn or aftermarket?

 

This is a long shot but check the 2 small wires that go to your transmission for the reverse lights(gotta get under your car). They are located on top of the transmission. I had a similar problem with intermittant fuses blowing and that is where my trouble came from. The open wires would short the fuse when i did extreme cornering or hit a bump and take out some dash instruments/ radiator fans and I think brake lights too. I just can't remember which fuse it was but it was either a 10 or 15 amp.

 

If you wanna do it the REAL old school way then wrap the damn fuse in aluminum foil, pop it back in and wait until you see smoke, when you do you found your short . No **** I have seen several very old "old school mechanics" do this and say they've never done it any other way in all the years they've been working on cars...but I wouldn't suggest trying it.

 

The "old school mechanics" never had ECU's to burn out.