Headlights dimming when braking

[CalMac]

Suspect alternator but don't have a multimeter. Is this the likely culprit? No warning lights on the dash until I pulled up outside just now and the PAS light flashed on for 2 secs (weird as I thought I didn't have PAS lol)

Car has been fine up until this evening, just noticed that every time I got on the brakes coming home tonight that the lights were dimming and my HU kept restarting as I was driving. Turned HU and all other electrics off for the drive home but the dimming persisted.

New Bosch S4 battery fitted 3 weeks ago.
HKS circle earth kit
Headlight bulbs are Osram, maybe 6 months/1500 miles old

I've noticed in the last week that I'm getting some high-pitched whining through my speakers that changes with revs, could this be related?

Sorry I know this must've been covered before but I couldn't find any threads on it

Getting so fed up of niggling stupid problems all the time with these old cars now, seems I get maybe one day of enjoyment then 2 months of needing parts/waiting for motivation to sort stuff Especially when as far as I'm aware I don't cut corners or buy cheap parts and always look after my cars, maybe I should just buy a Honda and be done with it

[Draven]

I have a Multimeter somewhere. If that helps.

[Draven]

maybe I should just buy a Honda and be done with it

We'll not tolerate such blasphemy on IMOC..

[CalMac]

Haha sorry

Might come in handy, thanks It's booked in at Northampton Motorsport tomorrow morning for geo setup so I'll get them to have a look at the alt and see if anything's loose, if they can't help then I may just come bugging you for the multimeter!

[Race Idiot]

Slightly similar problem I had, the whole dash would dim when I braked. It turned out one of the brakelight bulbs had a short in it. Might be worth replacing em first.

[ashley]

Worth checking the integrity of the main charging cable that bolts to the alternator...than can corrode and start to let go, maybe when you're braking it's causing the cable break to open.

[CalMac]

Hmm.. Both good ideas! Will check tomorrow

[abovetherim]

First thing i would do is check the battery terminals are secure and clean(including battery earth to body end). Both can be prone to coming loose as the original battery terminals were fatter than modern ones.

HU resetting could be a red herring here but also could be contributing to the problem. Pull the HU out and check no shorts in the back there.

Also check the 3 wire plug that goes into the alt.

The other thing to check is the bracket to body area of the coil as the bracket is and earth point for the igniter. Next to the coil there is also an electrical noise suppressor so you can check this is plugged in.