Electrical Issue
 

Hey guys

I'm having a big electrical issue with my car. It seems there is a short somewhere in my system. Attempting to start the car results in a blown 30A ACC fuse in the main fuse box, in addition to a lack of engine cranking.

The car was running fine till one rainy day. I parked somewhere, came back and the car would not start and my aftermarket gauges were dead, as well as the radio. Replacing the 30A ACC fuse let everything come back to life, but upon trying to start the car, the fuse blew again.

At a point in the past, the engine harness was compromised in the grommet that enters the driver's side footwell. I assumed that is where the problem may be, but would welcome any advice or pointers on how to isolate the problem.

It may very well be that the problem has nothing to do with the engine harness in this section at all, so if anyone has a thought, please let me know.

Thanks a bunch. If anyone needs a copy of the wiring diagram or something, I can send it.

If you have a wiring diagram, that is the tool to help troubleshoot your issue.
You need to follow the path after the ACC fuse.

First pull the ACC relay and start the car.
The charging and starting systems are after the ACC fuse, but before the ACC relay.
Keep in mind that some things like the audio system and cigarette lighter will not work because they are in the ACC circuit after the ACC relay.
If the fuse still blows, then you know its somewhere with the charging/starting system.
If not, then continue past the ACC relay.

You also mentioned aftermarket gauges. Did you tap into anything within this circuit?
If so, double check your connections and make sure its not shorting anywhere.

Unfortunately, these kinds of issues are worked-out by process of elimination... you just need to know where to start (which in your case is the ACC circuit).

I would start by disconnecting your add on gauges......if it fixes it there is likely a wire pinched with a short to ground.

Add on wiring without protective sheaths is often a problem in the long tern on an auto...its a hot and shaky world in there and the failure rate is high.

Thanks for the replies guys... I really appreciate it.

So we pulled the ACC RELAY and dropped a fresh 30A ACC fuse in and tried it and it instantly blew with no cranking at all.

So this seems to be a short in the starter/charging system somewhere? We didn't really touch that during any mods. We did upgrade the ignition coils, but that's not on the starter circuit is it?

Danno, we triple checked our gauge wiring and there is nothing wrong there..

We also exposed the harness through the firewall where it was damaged previously, and all those repairs are perfect... so it doesn't seem to be the harness.

Jon, can you walk us through where to start troubleshooting the starter/charging circuits?

Thanks guys...

Sure.
First lets look at the ACC circuit:
Attachment 138961
I highlighted the path in red to follow easily.
As you can see, when the ACC relay is pulled, there is only one other path to follow.
That is the Starter/Charging section.

Looking at that diagram shows the following:
Attachment 138962

Now you mentioned that it blew without cranking.
What exactly did you do when it blew?
Did it blow when the fuse was inserted?
Did it blow when you pressed on the clutch pedal (if you have an MT)?
Did it blow when you turned your key to ACC?

The car is an 04 MT. The fuse blew upon turning the key to the START position in an attempt to start the engine. It did not blow upon pressing the clutch in, only when turning the key. It does not blow in the ACC position.

Is there any weak point you know of in the starter/charge system that could present in this kind of problem?

Thanks a lot for helping us out. I appreciate it alot.

As you can tell by the "Starter Circuit" diagram I posted, when the key is turned (like when you are about to start it) it allows a small voltage to pass to the starter interlock switch.
When you have your clutch pedal down, it presses this switch to allow the current to pass onto the starter relay and energize it.
Once the relay is energized it flows to the starter (specifically the solenoid on the starter) to move the drive gear to the flywheel and turns the starter on.

So with that said, my next place to look is the starter.
You'll see two wires going to the starter.
The one enclosed in a white case is ALWAYS energized, so its likely not that (unless its touching the other terminal).
But use caution around it, might be a good idea to unhook the battery before going under there.
The cable just to the left of it is coming from the starter relay and goes into the starter solenoid.
I would check there.
Attachment 138963

Thanks a lot for your help and pointers. I think I am about ready to send the car to Mazda now that I am confident that this problem is not the result of any damage or modifications that I was responsible for. I am happy to have diagnosed at least that much.

One last question though, if the starter motor had somehow failed or siezed or blown, could that be a potential cause for an electrical overload like this?

Thanks again

Unlikely since the main supply is directly from the battery.
The current from the starter relay side is just to activate a solenoid in the starter.

I would have been curious to see what would happen if you swapped the ST and HEAD relay.
We really did narrow it down pretty good (as long as you really did pull the ACC relay in the beginning).
Attachment 138978

I'll keep you apprised of what the problem turns out to be. Yeah, I did pull the correct ACC relay out and the 30A fuse still blew, so the cockpit seems to be in the clear, and I visually inspected all of the wires in the previously damaged section of the engine harness, but the Mazda guys did a phenomenal job of repairing it.

Edit: on a side note, what software did you use on those pics?

I use Microsoft Word to generate the text box and arrows.
Then I use PhotoShop to customize the resolution and quality so that I can attach the best quality pic while staying within the site's 209.8 KB rule for jpeg.

Aright, riddle me this. How can I turn my key off and take it out, and still have my engine be running? No, I do not have a turbo timer...

Ya, so I got the car back from Mazda, they said it was a relay that was shorted out internally. When I went to pick my car up, my battery was dead. I thought that was curious but shrugged it off as I have what I consider to be an undersized battery and it dies easily if not cared for properly. So I get a jump start. Car starts up fine, blows no fuses, everything seems in order. My fuel is very low though. I shrug that off, because I had no idea how much fuel was left before I gave them the car.

I make it home, and park the car. I turn the key and take it out. All the cabin instruments turn off as expected... however, my engine is still running. So I was at a loss of what to do, so I killed the engine via stalling. With the engine dead, I could clearly determine that my throttle body was still powered and my radiator fans were still going at it.

This is why my battery was dead, the car is not actually turning off, and all the fans and electronic engine components killed the battery. It may even explain my low fuel level, if the engine kept running for a long while after they parked the car. I disconnected my battery and left it to trickle charge while I fish for a solution.

Any clues?

Damn... I was thinking it was a shorted relay or something within the fuse panel.
Oh well, at least Mazda verified my suspicions.

I wonder if they just swapped the Ignition relay with the Starter relay for troubleshooting.
Remember, I asked you to swap the Starter relay with the Head (headlight) relay?
So try swapping your Ignition relay with your Head relay and see if the car shuts-off.
Now if this works, your headlights might stay on because the relay is shorted (if my suspicions are correct).
If the car does shut-off after swapping the relays, disconnect the bad one and purchase a new relay.

Ooh, so I still didn't stump you yet eh? I thought that this problem woulda shocked ya :lol:

I'll give that a shot when I get the chance, will let ya know.

Once again, thanks a bunch.

I can be a persistent SOB every now and then ;)

Interesting issue. Subscribing.

Ok, I swapped the relays for Head and Ignition. The car now starts and shuts off, and the headlights still function properly. This seems odd to me, but whatever.

Granted, this has only been one test, and I will keep everyone posted on how things progress from here.

Thanks for the tips Jon.

Glad to hear that worked.
I would still purchase another relay if I were you.
Maybe the contact in the relay was stuck and when you removed it to swap it, the contact became free.
Doesn't mean the problem can't come back.

Oh I see, that makes sense. So now that the faulty relay is in the headlight socket, assuming it became stuck again, my headlights would remain stuck on, or off depending on which way it got stuck?

Correct.
That is assuming the contact was stuck all along.
Which might also explain why the dealer thought it was OK after they swapped the relays (which is what it looks like they did).
It worked for them but it stuck when you tried it.
Maybe you had the contact engaged longer than they did so thats why it stuck for you and not them.
They probably ran it long enough to drive it out of the garage and park it.

Ugh, went back to start the car again, no crank, just clicking sounds (I think from the relays). Went to make sure the relays were installed snugly, and upon applying pressure to the Head relay, the lights went on. So that relay is stuck on (note that this Head relay was originally the relay in the Ignition spot, which caused the car to not turn off).

I don't understand how the car can be not cranking now, when it was a mere couple of hours ago. Granted my battery was a little low, and I am now charging it, but even with a low battery I would normally get a very weak crank.

Interesting....
Depends how low the battery was.
The starter gets all its power from the battery.
Lets just see what happens once its charged.

I am starting to wonder what they actually did as "repairs" when I left my car with them...

After charging, the car started up. I have removed the faulty headlight relay for now, so I am without headlights until I replace that relay. I suppose the matter has been resolved, but will give an update in a few days to confirm.

Thanks for the help Jon, you really helped me make sense of something I had no prior experience with.

Weird. Good Trouble Shooting.