Hi all,

I have a crash damaged ford focus mk4 1.0 mhev st line x manual (maybe im regretting it now). Ive been working on it for some time as a project, the passenger side took a hit and as a result it ripped the connector in front of the ecu (not the ecu or its connectors, this is a different connector, mainly responsible for powering/communicating with the gearbox, bisg and a few other bits not engine related).

Referencing the wiring diagrams, i was able to solder all the wires back and the car had no more error codes, the car started up fine and I was able to bring the car forward and backwards many times. Fast forward to today, where i swapped the damaged radpack with a new one and tidied up my wiring work with cloth tape. Car ran fine let it idle for about 40mins with radio / navigation heated seats on etc as I was testing out everything. At the end of the day I went to park the car in its spot and as I put it to first gear and moved a bit the car completely shut off. The car then had no power at all but I still had interior light. No dash, no ignition nothing. Then somehow it came back on I plugged the scanner in a quite a few errors related to communication (which to me seems more like low voltage to abs, bcm etc), Went to turn the ignition off and on, and then it had no power and has had no power ever since. The interior and wing mirror lights do work, and the door does lock after spamming it a few times randomly it would lock (the mirrors now do not fold), which I find strange, I thought if the BCM is dead it cant lock, but it can lock but then the mirrors don't fold...

Is there anything that I can take a look? Battery (new battery installed) voltage with my battery trickle charger was around 13v. To my knowledge there isn't any grounding points to the chassis/engine where the impact was. Its strange how out of nowhere whilst moving slowly the car died instantly, when I managed to get it on briefly it had service error and hand break malfunction. I would have assumed there is no power form battery but if the car has lights on and was able to lock (though not fold mirrors) there is definitely power.

Would greatly appreciate any advice from ford wizards here.

TIA

22 minutes ago, elco_benoz said:

Battery (new battery installed) voltage with my battery trickle charger was around 13v.

Hi,

That doesn't tell us anything about the battery. Just that your trickle charger is giving it 13v.

Need to test battery with the engine running (appreciate it's too late for that now).

And again at rest, after having been left overnight. It definitely won't be 13v.

However, if it is a brand new battery, even if the generator isn't charging it, I wouldn't expect it to die after just 40 mins running a petrol engine in summer without any electrical consumers like heated screens etc. To me this does feel more like a bad connection, or a frayed cable. So all the voltage can get through. But not enough ampage to power the items. Battery terminal is the obvious place to start, checking that they are clean and tight.

1 minute ago, TomsFocus said:

Hi,

That doesn't tell us anything about the battery. Just that your trickle charger is giving it 13v.

Need to test battery with the engine running (appreciate it's too late for that now).

And again at rest, after having been left overnight. It definitely won't be 13v.

However, if it is a brand new battery, even if the generator isn't charging it, I wouldn't expect it to die after just 40 mins running a petrol engine in summer without any electrical consumers like heated screens etc. To me this does feel more like a bad connection, or a frayed cable. So all the voltage can get through. But not enough ampage to power the items. Battery terminal is the obvious place to start, checking that they are clean and tight.

Hi Tom,

New battery, was fitted when I got the car as old one was dead. Your correct the trickle charger was charing at 13v but before it charges it tells you the voltage and it was round 12.5 or so. I doubt this is battery and as you said, a new battery and the car is running idle for 40mins then randomly died whilst the engine was on and moving.

I am confident that the battery terminals are all secure, is there any placed that you would recommend to check first such as mega fuses etc ?

thanks

13 minutes ago, elco_benoz said:

Hi Tom,

New battery, was fitted when I got the car as old one was dead. Your correct the trickle charger was charing at 13v but before it charges it tells you the voltage and it was round 12.5 or so. I doubt this is battery and as you said, a new battery and the car is running idle for 40mins then randomly died whilst the engine was on and moving.

I am confident that the battery terminals are all secure, is there any placed that you would recommend to check first such as mega fuses etc ?

thanks

I can't think of any fuse that would cut power to everything except the odd light and door lock. You could check every multiplug on the fusebox under the bonnet and inside the car just in case the impact dislodged any of those, but that seems unlikely in all honesty.

I really do think it'll be one of the thick cables from the battery. Even if they seem tight, they may be slightly bent and not making good contact. For 5 minutes work, I really would remove, check and then reseat those before moving on to anything bigger. To rule out the negative cable, you can attach a jump lead directly from the negative battery terminal onto a thick metal part of the engine or chassis. These leads can break internally from a sharp jolt, but it only takes a tiny movement to make the connection again inside.

Edit - I've just remembered there is a fuse on the positive battery cable for these. I can't really believe that would have blown from just moving the car slightly. Might have cracked at one end though.

On 5/18/2026 at 9:16 AM, TomsFocus said:

I can't think of any fuse that would cut power to everything except the odd light and door lock. You could check every multiplug on the fusebox under the bonnet and inside the car just in case the impact dislodged any of those, but that seems unlikely in all honesty.

I really do think it'll be one of the thick cables from the battery. Even if they seem tight, they may be slightly bent and not making good contact. For 5 minutes work, I really would remove, check and then reseat those before moving on to anything bigger. To rule out the negative cable, you can attach a jump lead directly from the negative battery terminal onto a thick metal part of the engine or chassis. These leads can break internally from a sharp jolt, but it only takes a tiny movement to make the connection again inside.

Edit - I've just remembered there is a fuse on the positive battery cable for these. I can't really believe that would have blown from just moving the car slightly. Might have cracked at one end though.

On 5/18/2026 at 9:16 AM, TomsFocus said:

I can't think of any fuse that would cut power to everything except the odd light and door lock. You could check every multiplug on the fusebox under the bonnet and inside the car just in case the impact dislodged any of those, but that seems unlikely in all honesty.

I really do think it'll be one of the thick cables from the battery. Even if they seem tight, they may be slightly bent and not making good contact. For 5 minutes work, I really would remove, check and then reseat those before moving on to anything bigger. To rule out the negative cable, you can attach a jump lead directly from the negative battery terminal onto a thick metal part of the engine or chassis. These leads can break internally from a sharp jolt, but it only takes a tiny movement to make the connection again inside.

Edit - I've just remembered there is a fuse on the positive battery cable for these. I can't really believe that would have blown from just moving the car slightly. Might have cracked at one end though.

Thanks Tom, turned out to be loose BJB was not fully seated.