Bad Alternator or Headlight wiring issue?
 

New thread as I have figured out kinda what is causing my drain. Now just Why so I can know if I need to replace the alternator or not.

• Battery has been load tested
• 12.68v left overnight disconnected. It holds charge.
• 9mA draw when off, so it is not draining when the car is off.
• With NO accessories on, 13.98v running
• With ALL accessories on (EXCLUDING HEADLIGHTS), 13.65v running
• With NO accessories on, ONLY LIGHTS, 12.7v running.

Is this a bad alternator, or some kind of weird excessive draw in the lighting system? After a 15 minute drive the battery will be close to dead when I try to start it up again. I can drive during the day numerous times without an issue as the lights are not on, but as soon as I drive with them on, battery dead.

I have replaced the voltage regulator....

Funds are a little tight right now...otherwise I'd just replace the alternator so I want to make sure it IS the alternator before I do it.


Thanks

I think it is the alternator. Have your Alternator check.

Electrical
 

13.98 (Engine Running) with NO loads, is a little low.
It will however Maintain a good battery.

12.7(With only the headlights on) is not enough to charge the battery.

(Even though we call it a 12 volt system,you've gotta have at least 13 V
to even maintain a fully charged battery,with no loads)

I'd check the charging system wiring and grounds.

[Example: I've got a domestic that's showing 13.85 V @ Idle (No Loads) 128 K.
It's manual says to replace the VR if it's not putting out 14. V to 14.5 V.
'Ordered the new VR last week,after checking everything else.]

[Yamaha shows 14.41 V @ Idle OR @ WOT, with or without EVERYTHING including the Bilge Pumps,Trim Tabs and Engine Tilt (80 Amps draw) ON.]

Is there a way to test the alternator individually or does it require removal and bench tested?

I've heard I can probe the alternator directly to confirm running voltages...can this be done on ours? I don't remember seeing anywhere to probe, but maybe I am wrong.

Maybe that aftermarket fog light system has something amiss. Do the wires in that system become "live" when your headlights are on? It is possible that a problem in that system could cause too much amp draw.
Regards, Eric

there isn't anything wrong with your alternator.try turning on the oem lights only and check voltage.i think those extra lights may be your culprit.if this is a 201 or 124 the charging system was marginal anyway.i seem to remember that if you start those cars on a hot day,turn on air,and aux fan starts,after about ten mins you could watch the voltage drop slowly as the alternator could not keep up with demand at idle.

With the main beams ON, it is 12.7v...
With the main beams AND Fogs ON it is 12.65v...

I will disconnect the fogs completely and try it although I don't think the 'fogs' are the issue. I am using the OEM Bosch fog lights that were used with the AMG kit. I simply removed the connectors at the fog light and wired them into it...so my fog lights in the main assembly have been replaced basically by the lower ones.

Since I am new to this type of stuff, could you give a more layman description on how to check for 'live'. Am I just checking for voltage at the fog terminals or what?

Different setups are set up differently. There are setups where the fog light switch only has power going to it if the headlights are on, causing any defect in the fog light system to only manifest itself when the headlights are on, even if the fog lights are not on. Other fog light set ups are live all the time, just like the headlight system. In a situation like that, a problem in the fog light's system could cause a power drain all the time, even when the car is off. Either way, a problem in the fog light system could cause a power drain if that system is live (has power running to it) even if the fogs are off.
Regards, Eric

are the main beams oem?

Oh yeah, that's a good question too. In the pics it looks like those have been changed too. Another potential problem area.
Regards, Eric

I'd go somewhere that can load test the alternator installed.


Not sure measuring voltages will tell you. Just check the idle and max amperage @1500 rpm. Then see where it sits versus the specs.



M

You probably have the 70 amp alternator which in reality barely cranks out 55 amps at 3000 rpm. At idle it probably puts out 15-20 amps which is not enough to keep up with the latent demand, much less aftermarket headlights or the auxiliary fan. This is a known problem with this alternator. You need to upgrade to at least the 80amp alternator that was installed on later model 124's or if you crave more juice (aftermarket stereos and amps) upgrade to the 143 or 150 amp alternator installed on later MB's. Plenty of posts on performing this upgrade. Mark

Yes I have the 70amp alternator. I'll see if I can get somewhere to load test it so I'm not chasing electrical gremlin theories I guess....

If the alternator is the issue I would like to upgrade to the 80 amp...any bigger and I think it'll steal too much hp which I lack as it is with A/C on. How much would the 80A steal from me?

80 Amp VS 70 Amp is a negligible gain
 

If you're gonna go to the trouble of an upgrade... 142 Amp or the 150 Amp.

you've got to go for the 150...... i don't know what mb was thinking with the smaller alternator....