CrazyDude

I am trying to troubleshoot electrical issues with my car (low voltage < 2Krpms) ; I'm not sure if it's a bum alternator, bad grounds, ghosts, etc.

I measured the voltage in my dash, in the cigarette lighter socket, and it is 0.3v lower than the battery voltage. Is this normal? If not, any recommendations on what might be suspect? (this is an S5 NA)

I'm going to go and redo all the big grounds (bat terminal, starter, ECU @ intake, shock tower, under T coil) when it's not raining outside, but are there some relays or anything else that would affect this drop or which are commonly problematic?

Thanks!

HOZZMANRX7

iTrader: (43)

Considering the number of connections between the battery and the cig lighter, and how years of corrosion at each connection has built up over the years creating resistance at each of those connections, .03 volt drop is actually pretty darn good.

CrazyDude

It's not 0.03v, it's 0.3v , as in 3/10 , or roughly "one third" of a volt.

john ward

iTrader: (7)

Not that bad still.

HOZZMANRX7

iTrader: (43)

Honest, I understood what you said. And I still stand by that .3v drop comparison between the battery and the cigarette lighter isn't bad at all.

Furb

iTrader: (2)

You answered your own question...

The problem has a relation to your rpm's, so that's an alternator issue

HAILERS2

The power for the CIGAR goes (depending if the alt is putting out or not) from the battery.........to the engine bay fuse box.........thru the Main Fuse.......to the ignition switch...........thru the ignition switch............to the CIGAR fuse.........to the cigar receptacle.

But that same CIGAR fuse also feeds other items (remote mirrors etc) and the power from the ignition switch to the CIGAR fuse also feeds the 20a Audio fuse and whatever that audio fuse feeds into.

Look at the wiriing diagrams in the series five manual and page W-1 and you can see that path right there.

IF the engine is running then the path is from the Alternator output wire to the ignition switch and the rest is the same.

I don't think .3vdc is worth talking about myself.

MazdaMike02

iTrader: (4)

.3v is an acceptable voltage drop. There's quite a bit of wire from the fuse box to the accessory socket. I would verify voltage of the battery, 12.6v is fully charged. Running it'll be between 13.6-14v depending on ambient temperature. Although all 2nd gen owners are aware of the sub par charging capabilities of our alternators. You'll be lucky to see 14v on a good day. Anything less than 13.5 is low, check at 1500 rpm as well with loads on, high beam, fan on high, rear defrost.

dave007

iTrader: (1)

.3v drop is good, but are you measuring in the actual socket, or at the connector that plugs into the back of the cigarette lighter socket? The cigarette lighter socket itself deteriorates after 20 years, and does a poor job of passing any current.

Also, alternator would not cause the problem you are seeing. An alternator problem would result in low voltage at the battery as well as everywhere else. I agree with MazdaMike02, about below 13.5v being low, but sometimes you're lucky to get that at idle on our cars. I'm happy to see 13v, and then see the voltage come up off idle.