The only place for a coil spring is up Zebedee's arse.
Joined: May 29 2019
Posts: 1

Hi All

I'm new to the forum, so hello first before I ask you for some advice.. Hello!

I'm the owner of a '96 P38, 88k miles. Had it about a month with some issues and barely any service history... However, Ive been working through the gremlins, given it a full service of oils, filters, plugs etc so its having some TLC.. However,....

Having done all the usual electrical checks and made some recommended upgrades (additional positive cable from alternator to battery, new alternator, new battery, cleaned battery earths and added a new one etc etc) I find I am having two issues, maybe related..

I have a very intermittent Alternator Fault pop up now and again (seen it three times in a month, only for a moment) and also the usual SRS Light which was on when i bought it but is increasingly now more off (good?!) than on - although it comes back...

To my question - I have a good 14.7 v from alternator to battery with barely no voltage drop, but I have only 13.8v at the alternator to BECM wire (small brown and yellow one).

Is this OK? Im wondering if 13.8v is recognised by the BECM as 'not enough' and causing both my intermittent Alternator Fault and the SRS fault (which oddly seems to be fixing itself since i added the extra charge cable.....

Can I just add another wire from the alternator direct to the BECM if it is fried and unreliable?

Thanks for any help in advance..


Joined: Dec 30 2015
Posts: 4680

14.7V seems a bit on the high side. Early cars had a different alternator that charged at around 13.8V but later cars were fitted with batteries with a higher Calcium content that can withstand a higher charge voltage so the alternator fitted to later cars tend to regulate at around 14.2V. The small brown/yellow wire is simply a charge sense so anything over battery voltage is normal and should be recognised as the alternator charging. Might be nothing more serious than the connectors to the BeCM needing taking off and given a squirt of contact cleaner.

The SRS light is an odd one. On a pre-99 car any fault on the SRS system will bring on the light but normally it will stay on until reset with diagnostics rather than go off once the fault clears. It is only the later cars where it goes off once the fault is cleared.