Electrical Help!

Damski · Post by **Damski** » Fri Sep 17, 2021 8:36 pm

if this is in the wrong section please do change it.

so my 97' BB9 has a v odd issue. when driving at times all the electrics in the car Ramp up, Fan gets louder and headlights get so bright they burn out instantly. The cluster also gets much brighter and an ABS light comes on until I slow down then the voltage would appear to return to normal... Is it the alternator or an electrical gremlin? any help appreciated

Post by **Vtecmec** » Fri Sep 17, 2021 10:37 pm

There is a voltage regulator in the alternator, which can be changed. I'm sure there's a test procedure in the manual for it.

Damski · Post by **Damski** » Fri Sep 17, 2021 11:28 pm

ah didn't realise. Thanks Vtec I'll give that a go on Monday

Scott560 · Post by **Scott560** » Sat Sep 18, 2021 9:44 am

Yeah sounds like the alternator regulator to me. I would avoid driving the car in the meantime, as the overvoltage could damage more than just bulbs (I saw a car once set the headunit alight lol at 17volts haha).

The normal alternator does have a slight 'step up' in voltage above idle speeds, which does cause the interior fan to go faster, but that's normal.

89 UKDM BA4 4WS (resto job!) · Post by **wurlycorner** » Mon Sep 20, 2021 12:01 pm

Section 4-22 of the 5G service manual describes how to fully test the charging system - there's a limit to some of the tests you can probably do in there though (you're unlikely to have a variable load device?).

There is a chance it isn't alternator related, since the ELD monitors voltage and the ECM also acts to tell the alternator what to do, but that's unlikely.

Agree with others on here - if you're blowing bulbs, that suggests your voltage is going dangerously high. You risk blowing all the ECU's in the car if you keep driving it like that.

Start by doing a quick check of the voltage across the battery when it's running/causing the symptoms you suggest - if it's higher than 14.4v, switch if off and don't start it again until you've fixed the fault!
Also do a check for AC voltage, not just DC (you shouldn't have any AC, but can do - if the rectifier in the alternator is failing).

YouTube · Post by **Sailor** » Mon Sep 20, 2021 10:09 pm

What he said.