On 1/11/2011 9:52 PM, audiolaw@aol.com wrote:
Thanks, I haven't measured voltages yet. I did check for current draw with everything off. I was showing .00 to .01 amps between the battery and the cable. Opening the door increased the reading to approx .7 amps when the interior light came on. I'll move on to chasing wiring.
In a message dated 1/11/2011 6:37:51 P.M. Pacific Standard Time, alstheone@verizon.net writes:
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Subject: Interesting alternator problem Date: Tue, 11 Jan 2011 21:08:06 -0500 From: Alan Boucher <alstheone@verizon.net> To: diesel_mercedesl@yahoogroups.com
My 83 300D has developed an interesting problem. After 2 or three days of normal day and evening driving the battery dies. The car is in NY and is driven 15 to 35 miles at a time. The battery is approx. 1 Yr old. Now the red light is coming on. with no load on the electrical system, clean battery and ground terminals, and a fully charged battery, it does dim somewhat with increasinng speed. The local Autozone tested the alternator in the car and a spare and said that both were good. I swapped out the alternator with the spare, one of my favorite jobs on this car, with the same result. I checked the brushes in the voltage regulator and cleaned the commutators on the spare before I put it in. The only thing that I can't verify is that the voltage regulator is working properly. My next step is to change the voltage regulator. I have another alternator that was working when the car was wrecked, but its under a couple of feet of snow. Does anyone have any suggestions?I suggest that you NOT check the regulator or do any swapping, YET.Assume for the time being that Autozone is right, that the alternator is OK. Then you want to find out if the unit is charging IN CIRCUIT and if it's charging the battery.If the red light is coming on, it is telling you that the electrical system is seeing drain, rather than charge. Find out why. With the engine running OVER idle speed (not much over), use a simple VOM to measure what the voltage output of the alternator is. It should be over 13 vdc.If it is over 13 vdc, then measure the voltage across the battery terminals, it should be essentially the same as the alternator output. If it is NOT, then you have a wiring problem.With the engine OFF, is the battery being drained? How do you know? Lift the + terminal cable. Connect a test light between the + terminal and the cable. Does it light? If so, you have a significant drain.Find the drain by pulling fuses, one at a time, and see which one stops the drain.None of this is brain surgery - much more like rocket science, simple steps of isolating the source of problems, one at a time, to see where you have trouble.On this car, you can suffer problems with corrosion where major cables run and interconnect. You may have a really simple cleaing problem to deal with. Look in the archives for Nate's design for an improved grounding cable set up. His design was essentially done to address similar problems in charging.Tom
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