Driving yesterday my accord turned off and on for a split second whilst driving, while I was putting the windows up (happened twice in a short period of time)

Seems like its shorting somewhere. It flicks off and on quickly while under load (putting windows up, flashing high beams etc). Happens quick enough that car keeps driving, but obviously worried it'll go off and not come back on! Didn't happen this morning, but I wasn't running the heater or my lights.

Chucked a multimeter on the battery, read 12.5v while off and 13.7v when running. So that seems OK?

2003 Honda Accord Euro. NZ New. 2.4L 5 speed auto

Any help would be appreciated!

 

A short in the electrical system causing the car to shut off would cause a fuse to blow, so I don't think a short is your issue. A momentary loss of voltage like you describe can be caused by a bad/weak battery, damaged battery cables or poor connections on any end of the battery cables, or the electrical portion of the ignition switch loosing contact. A loose main fuse (80 or 100 amp) or corroded contacts could also cause this.

To begin, test the battery voltage with the car not running and turn on the headlights. The battery voltage should start at about 12.6V and quickly approach 12.0 and keep dropping. If the battery voltage immediately drops to 10.4V, then one of the cells is dead in your battery. Your car battery is essentially 6 individual 2.2V cells (6x2.2 = 12.6V) hooked in series.

Then repeat the same test with the engine running and load the electrical system with the headlights on, blower running, rear defrost on, radio on, etc and read the battery voltage. The battery volage with the alternator charging should be >13.3V.

You can also try voltage drop tests on the battery cables to see if one of your battery cables has internal resistance or a connection problem. You can also try shaking the key in the ignition switch while the engine is running to see if you can get the engine to stall out.

You might want to disconnect the battery cables and clean the eyelets and bolts at all ends of the battery cables with some sandpaper or a wire brush to ensure you have good connections.

I would not start throwing parts at the car unless you test a component as failed.

 

Thanks for the incredibly detailed reply, I appreciate it.

Did not have a chance to test the above last night, but this morning when starting my car the radio and clock had reset, as if the battery had been disconnected.

 

It is strange that you had enough battery to start the car, so I don't think your battery is the main issue. I'd definitely look at the voltage drop tests and inspect the + and - connections at the engine bay fuse box.