Battery wired in reverse fuses blow continuously

[nightSpirit]

Hoping someone can help me!

Monumental tit that I am, I wired up a new battery in reverse for a few seconds earlier and now 2 20amp fuses blow any time I try to replace them and the car doesn't fire (will crank) radio also dead.

Engine is 2ltr tfsi and the 2 fuses lead to the ecu....anyone got any ideas?

[t955daytona]

Forgive me for asking the obvious but I take it you have now correctly wired the battery? If this is the case I strongly suspect you may have fried the ECU when connecting incorrectly. Check the relays to the ECU also as you may have overheated one but I would thenk the fault lies with the ECU?

[nightSpirit]

Absolutely, the battery is now wired correctly. I think after a couple of sparjs as the cable touched it was then connected for around 4-6 seconds...what an idiot!!

There are 2 20a fuses that blow whenever i fit a new one (car turned off) but other than radio fail and car not actually firing everything else seems to be working fine.

Any way to test the ecu?

[mattyc69]

What are the fuses that keep blowing for?

[anonymous-user]

The Op has already said they are ECU fuses which suggests he is sadly about to learn a very expensive lesson

[nightSpirit]

That I can't say for sure. They're on a random block going to the ecu (engine and ecu is no longer in an Audi). It's 2 20a fuses that must be perm lives for something (1 for radio??)

[nightSpirit]

I will test everything later and check ths radio itself. I obviously need to fix the shorts but could the ecu be causing them?

[Chippo1]

I would have thought almost any of the electronic systems will be fried , they don't like DC up them the wrong way corporal Jones !

Unless the supply point has a Bridge rectifier stuck on the supply point to protect against numpties, but I suppose Mr Audi would see this as a way of making lots of wonga

I mean the alternator has a nice rectifier to sort out the polarity in the first instance and the battery big + - terminals so whys put protection and add complexity , just make money when some one gets it's wrong !

[nightSpirit]

I've checked all the fuses I can see and those are the only 2. Let me check lights etc later and reply...could the ecu being fried cause the radio to die though? 180 for an 8p tfsi ecu isn't bad though if that solves it all (will need a remap)

[nightSpirit]

Some pics if they shed any light at all? Thinking I need an auto electrician to visit me...

Can't see any burnt wires and everything works (lights etc). I also think the new battery (harley battery like the Braille race battery) might now be fooked.

[Rich_W]

Remove the blown fuses
Unplug the ECU completely.
Refit fuses

PRAY they still blow. If they DON'T blow again fault is in ECU (i.e they only blow when ECU is connected)
If they do blow then fault is elsewhere in wiring.

Disconnect everything
Try and disconnet the loom at every multiplug point
basic continuity test on multimeter
one end to eart point
touch each wire one at a time until you get continuity to body/earth
faults in that wire

[AndStilliRise]

Rich_W said:

Remove the blown fuses
Unplug the ECU completely.
Refit fuses

PRAY they still blow. If they DON'T blow again fault is in ECU (i.e they only blow when ECU is connected)
If they do blow then fault is elsewhere in wiring.

Disconnect everything
Try and disconnet the loom at every multiplug point
basic continuity test on multimeter
one end to eart point
touch each wire one at a time until you get continuity to body/earth
faults in that wire

^This

[nightSpirit]

Thankyou, I will try ecu tomorrow and go from there.

[nightSpirit]

Right,

I've found another bank of fuses in the front of the car and 3 of those had also blown (3-7.5a) so I've replaced them and now the radio works!

I unplugged the ECU and fitted the 2 20a fuses and they didn't blow. When I connect the smaller ECU plug (left one) all fine, when I connect the large right one, both blow. So is that 100% confirmed that the ECU is shagged before I get an auto electrician out and buy a new ECU?

[nightSpirit]

Also can anyone recommend an ecu test/repair place? I'm in Leatherhead area.

[Adrian E]

Try BBA Reman - they're outskirts of M25 area and work mainly be mail order. They should be able to fix yours, so long as it's not completely fried internally

[nightSpirit]

Thankyou.

[silentbrown]

Not wanting to add insult to injury, but don't modern batteries still have differently sized terminals for +/- to 'discourage' this kind of accident?

I dimly remember having to change a car from positive to negative earth, back in the mists of time...

[nightSpirit]

Im still in disbelief that I did this...been working on and building cars for years, even changed battery on this car twice already! The race battery just has 2 m6 bolt terminals.

[silentbrown]

nightSpirit said:

The race battery just has 2 m6 bolt terminals.

You're excused, then.

What's it going into - did I miss that part?