Auto-electrical problem

FunkyCatUK · Dec 1, 2024

Dear all,

Just wondered if anyone could solve this puzzle:

Today I changed the headlight bulb on my car. It all worked fine when fitted, but then -

When I took the ignition key out I noticed the headlights stayed on (I've had the car 10 years - they only work with the ignition key in).

I then tried to start the car and there was absolutely no cranking from the battery at all.

Checked the voltage and it showed 12.6v or thereabouts.

Tried to start again and no joy.

Noticed that the voltage dropped to 8.5 on turning the ignition key on, but absolutely no sign of the car trying to start at all.

Tried to turn on the headlights and the main beam (the bulb I changed on one side) were dead on BOTH sides of the car!

Key fob operated locking also seem dead (but battery shows back to 12v).

Checked if I broke, disconnected any wires on the headlight cluster but they seem to be ok.

Lighting and ignition fuses are both ok.

Not sure if any members would have any idea what the problem was.

Thank in advance

James · Dec 1, 2024

I would start by fully charging the battery.
Sounds like a flat battery to me.

littlespark · Dec 1, 2024

Even with a cheap multimeter, a car battery will read around 14V when healthy.

12V is too low.

Sounds strange that the lights remianed on whe ignition is off.... if it didnt work that way before.
Fault in the ignition switch/relay thats keeping the power on when it shouldnt?

FunkyCatUK · Dec 1, 2024

James said:
I would start by fully charging the battery.
Sounds like a flat battery to me.

littlespark said:
Even with a cheap multimeter, a car battery will read around 14V when healthy.

12V is too low.

Sounds strange that the lights remianed on whe ignition is off.... if it didnt work that way before.
Fault in the ignition switch/relay thats keeping the power on when it shouldnt?

Many thanks, both.

Did a jump start with a neighbour's car today and it started straight away. Battery was at 14.x v when running. Will go for new battery tomorrow (bearing in mind the immediate start from donor battery). Hopefully not some other electrical fault..

Cheers.