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Yup, swapping battery cables was a bad move. Did you say that you started the car with the battery cables reversed? Where is your battery located - in stock location (engine bay by driver side headlight) or elsewhere?
If I were in your shoes, I would check the vital electronics for normal car operations, such as the ECU and the Body CPU. When you smelled something burn did you investigate where it came from? After realizing your problem, did you connect the cables properly or left disconnected? If reconnected, did you attempt to turn on the car afterwards? When you checked all fuses, did you only check the fuse box at the driver's footwell or also the main fuse box inside the engine bay?
A similar experience happened to my FC. The link could be found here: 91 Vert Reverse Polarity. In that case, damage was isolated to the Body CPU and a couple of fuses.
Let us know what you find when opening up the ECU and Body CPU.
I havent had the chance to cpu. I had to leave so
engine fuses checked so far
Left battery disconnected
Sorry i forgot to add thati used jumper cables
the jumper cables were the only thing backwards
When i started the car was when i fixed the cables the right way
Allow me to understand your reply. Please correct me if I misunderstand you.
1. Battery is in its stock location.
2. Your car's battery was charged with cross-wired jumper cables.
3. You checked all fuses in the engine bay and they all checked good (after you noticed a burning wire smell).
4. Battery is currently disconnected from the electrical system of your car.
I have other questions for you:
1. Did you place the ignition switch to ACC, ON, or START with jumper cables still cross-wired?
2. Could you explain when the jumper cables were corrected?
3. How did you check the fuses? Did you pull each one and test it with a multimeter?
4. Have you checked the fuses in the driver's footwell?
5. Have you taken the battery to an auto parts store for load testing? It may be worth it for peace of mind.
As I stated before, I would remove then inspect the circuits of your ECU and Body CPU for any potential charring from over current conditions. The Body CPU may bear the brunt of this type of damage because of its relevance to the factory alarm and associated logic circuits. You may also want to consider checking the relays associated with starting the car. Relays are more robust than electronic components (transistors, capacitors, etc...) so they should not be overlooked. Moreover, you may also need to inspect the electrical connectors between key harnesses if you haven't seen any damage.
1. Yes
2. Yes jumper cables were backwards
3. Yes checked what i could
4. Yes disconneced battery before i left
1. Yes turned key while cables were crossed. Nothing happened
2. I corrected the cables after nothing happening and at that moment realizing what i did and then started the car
3. Only did a quick visual check before leaving
4. Not yet
5. Not yet
Thanks for posting the photos of your ECU and adding those remarks.
I agree, your ECU looks good, no evidence of damage. Yes, you can certainly see damage to a circuit board when you smell something burn. Before checking the relays, I would remove and inspect the Body CPU. It's the skinny black box next to the fuse panel in the driver side footwell. The main board to inspect will be the "surf board". Removing the back cover to the Body CPU is a PITA so try not to crack the cover. I use jeweler's screwdrivers to pry it open.
When checking fuses, it is recommended to use a multimeter to check for opens. This is important because the fuse may look good but could be bad. Most of the time, you can see the problem through the fuse window. However, you could be easily fooled while contorted under the dash and looking at a fuse with a flashlight or background light (what little light you block while in the footwell).
I did take out the cpu2 black one
although before this problem mine has symptoms of degredation(no buzzer, seatbelt light always on,no alrm system)
checked resistors and all were pretty good ohm readings(as well as other components but resistors looked off.
From a forum post i used its just good ol leakage
it came off when i cleaned them. It didnt look like they were burned just dirty
I completely removed driver fuse box and fuses
Nothing looked burnt and nothing smelled burnt either
Do these photos represent the Body CPU after the cross-wire jump?
All of that black stuff looks like capacitor leakage. Did you smell the board? Does it smell like electrical components burned up? Chances are you have a few capacitors that need replacement since you had problems with the Body CPU before.
yes ive never looked at the cpu before the incident
i did smell the board, and i had a friend smell it as well
we both didnt smell anything burned, just smelled like "old" dont know how to phrase it better
a lot of that dark stuff came off when i cleaned it
the back of it looks like nothings ever happend to it
(im hoping to try and rebuild the board in the future)
im just now realizing now ive been looking at your thread on the cpu2
i think the car sitting for 8+ years probably just degraded or 25 year old components
yes ive never looked at the cpu before the incident
i did smell the board, and i had a friend smell it as well
we both didnt smell anything burned, just smelled like "old" dont know how to phrase it better
a lot of that dark stuff came off when i cleaned it
the back of it looks like nothings ever happend to it
(im hoping to try and rebuild the board in the future)
im just now realizing now ive been looking at your thread on the cpu2
i think the car sitting for 8+ years probably just degraded or 25 year old components
rattlehead,
No worries, thanks for the compliment. There is a lot of good info on that thread. I recommend posting repairs of your CPU #2 to that thread, if that's the route you wish to take. I would also recommend taking a few more photos of the board at different angles so anyone could observe the full scope of damage to it.
Getting back to your current problem, I recommend that you measure the fuses, both from the cockpit and engine bay. Additionally, never install a fuse rated HIGHER than the circuit. For example, if the METER circuit is rated at 10A then use a 10A fuse. Never install a 15A fuse in a 10A circuit.
After the fuses are checked then move on to the relays associated with the alarm, starting, and charging circuits. Please pay particular attention to the connectors. Shine a light behind each connector and verify that each wire is isolated from the others. Speaking from a personal experience, my FD kept blowing METER fuses. Turned out the problem was in one branch of my fan control relays. Two wires melted the plastic insert and shorted together. This short caused the fuse to pop. It took months to find then fix the problem.
Damn i already sealed it up and put it back in the car
all my other photos came out blurry
As for checking fuses and relays beyond visual inspection
Id want to check with the battery installed
BUT
Maybe i should should check out wires first?
like you said you had issues with two wires melting and shorting
My reason for just wanting to hook up the battery is that i already started the car after switching the cables the right way. This could just be me being a bit impatient
I would encourage patience when sorting out an electrical problem. Remember, you smelled wires or electronics burning and you have not seen anything obvious yet. Be methodical to remove all doubt that your car is safe to apply electrical power. It could start a fire, electrocute you or a passenger, or burn up something else. The question only you could answer: are you willing to risk the reward of starting the car without problems or suffer the consequences of replacing/repairing more damaged components/wires?
Roughly 90% of all wire harness problems occur within 1" of a connector. Do not be too quick to slice up a harness unless the problem is verified to be along the length of wires.
I cannot properly answer your question without knowing more about your specific situation. All I know is that you smelled something burn during this cross-wired jump start and the car started despite the cross-wire. The Body CPU and ECU both look good, besides some leaked out capacitors on the Body CPU.
While you had the Body CPU removed, did you also inspect the Flasher CPU? That board is located on the bottom of the assembly. It is unlikely to be damaged but it would be wise to inspect it and remove any doubts about its condition.
Thinking back, could you recall where and when you began to smell the burning electronics? Did you see a wisp of smoke? Could it originate from the driver footwell or perhaps externally (like under the car)? Did you have the windows rolled down? Were there any unusual sounds or other indications? How did your instrument cluster function?
This may also be a good time to remove the instrument cluster and inspect its gauges for any damage. It's also a good idea to inspect the speedo board for any leaked capacitors since the Body CPU has evidence of capacitor electrolyte damage. Have you removed the cluster before?
ok im gonna all the connectors on the driver side and passenger first
i did take a look at the flasher cpu as well and it looked like new
I didnt see any smoke. i tried to smell for it on both sides of the car but i couldnt trace it. it was just in the car. driver door was open.
last thing i tested were the headlights which went up and down. radio as well seemed fine but thats about it.
after correcting the cables and starting the car. i let it warm up and all guages seem to work like normal, with the exception of speedometer since i didnt move the car
i can check the cluster since i have to pull it again due to a light not working well
When something electrical or electronic burns it emits a very distinct smell. The chance of wires melting without causing damage is exceptionally low. Would you elaborate to what connectors you checked? Are you using the schematics from the WDM as a guide? Additionally, does the car have an aftermarket radio or alarm installed? Check those connections because they tend to draw more power. Lastly, how are you checking the connectors and what are you looking for? Please tell me your methods and I may be able to offer better advice on what to check.
Generally speaking for your circumstances, I recommend looking for short circuit conditions between each conductor of the connector and to chassis ground. This would confirm no parallel paths to ground exist.
As of right now, iv only been able to check visually
for any obvious signs hoping i find something
ive looked at all connectors passenger side by ecu
in the driver side and Under cluster and center controls
I Could probably benefit from learning better methods
any links would be appreciated
Tüner: i only checked the pop ups before completely disconnecting the battery
the smell is currently gone ive been smelling every connector i can find. Ill be double checking tho
TomU: I really wish i didnt but the
my daily has the negative towards the back and im guessing my mind was thinking about the fd that way
also when i turned key to on position nothing happened
Then after really putting jumper cables the right way i got the car to start
I would think nothing of it except for the smell. Thats what isnt giving me any piece of mind
I don't know if it's true for Mazdas, but alternator diodes can get fried in reverse polarity situations,
depending on how the alternator charging circuit is configured ?
High current flowing the wrong way could defeat non conductivity provided by bridge diodes that convert alternator AC to DC volts.
I imagine your charge light would eventually come on, as battery drains, if one or more semiconductors were compromised.
You could check + monitor battery voltage, which would eventually drop below 12.5v.
The same could hold true for ECU signal voltage regulators, which are heavy duty transistor circuits..
Your ECU might not function within safe parameters, if reference voltages aren't reliable or compromised.
I would personally swap ECUs to be on the safe side. You can always compare reference voltages from a healthy ECU
alongside yours, particularly at heatsinked semiconductor legs, and if both are the same, keep this ECU as a backup.
It's not worth risking an engine if you smelled burning components.
Do you have any electrical test equipment, specifically a Digital Multi-Meter (DMM)? Do you know how to use one? You can easily watch some YouTube videos on how one is used to check various electrical conditions.
Performing a visual inspection solves part of the problem. Testing the wires with a DMM solves the remaining parts.
For starters, you should be organized when checking connectors. Otherwise, a connector may be overlooked. I would recommend that you print out a copy of each schematic of a system that you want to verify, such as the Starting & Charging System, Engine Control System & Fuel Control System, etc...
Each diagram shows the conductor orientation of each connector and each connector is labeled. You may cross off each connector to give you a visual indication that they passed your checks. This ensures each connector was checked and nothing was overlooked.
Other helpful hints when verifying wire harnesses include:
1. Disconnect the other end of the harness, where practical. You are verifying the wires and connectors and not the gear they attach to.
2. Chassis Ground is your friend. Use a bare metal screw or bare metal on the car to serve as a wire extension. For example, you need to check 2 connectors at opposite ends of the car (think engine bay and trunk area). Connect one meter lead to chassis ground and the other lead to the respective conductor. On the connector on the opposite end, connect the conductor to chassis ground. In effect, the chassis becomes a wire extension that connects to the meter lead. Does that make sense?
3. When checking for short circuits, as mentioned in Post 20, measure the resistance of each conductor to each other. Then test each conductor to chassis ground. This ensures each conductor is isolated from one another. You may also watch some YouTube videos on this type of test.
Here is a basic schematic that shows what I referenced above:
In this example, the conductor under test is the top wire, Conn 1 Pin A to Conn 2 Pin 1. The DMM's red (positive) lead is connected to Conn 2 Pin 1 and a spare wire is connected from Conn 1 Pin A to chassis ground. Additionally, the DMM's black (negative) lead is connected to chassis ground. Given this rough schematic, the DMM should read 0 Ohms (a short). A short in this instance is a good indication because electricity flows from the meter through the wire under test, to chassis ground, then from chassis ground back to the meter.
If the DMM reads "O/L" or something to that effect then the conductor under test is open. This is also known as "infinite resistance" or "infinite ohms". An open circuit would be bad in this instance because electricity should flow as described in the short circuit condition. This reading would mean there is a break in the wire. A repair would be necessary.
NOTE: This does not tell you where the wire is broken. It only indicates a connection is broken.
Next, one must check for parallel paths to ground. Given the same schematic above, this is easily done by moving the red lead down to Conn 2 Pin 2. Leave Conn 1 Pin A connected to chassis ground. In this instance, an open circuit is a good indication. If you measure a short from Conn 2 Pin 2 to Conn 1 Pin A then that is a bad indication. That means both wires are touching somewhere.
Continue to check for open circuits by moving the red lead to Conn 2 Pin 3. Again, leave Conn 1 Pin A connected to chassis ground. A good indication would be an open circuit.
Once completed, move the wire on Conn 1 to the next position then repeat the above tests. Repeat until all conductors are checked.
02-22-19, 02:15 PM
