SL/R129: 1992 SL500 battery problem
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Joined: Mar 2011
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R129
1992 SL500 battery problem
The check battery light was on again even though I have just changed a new battery 2 weeks ago , I asked somebody to check it and he said it was not the problem of the dynamo, can anyone help me?
Senior Member
Joined: Nov 2004
Posts: 282
Likes: 3
From: Bradenton, FL
'87 560SL Sold, '99 SL500 For Keeps
Several things I'd look at...
o Alternator output voltage-if below 12v, pull and replace the voltage regulator/brushes(Bosch OEM buy online for $35, easy DIY) Retest voltage output
o If alternator checks out ok when you first test voltage output, the next thing I'd do is, with the ignition key OFF, and a voltmeter, start pulling fuses one-at-a-time and check voltage...it should read 0. If you get a voltage reading, then you have an open loop current draw on the battery. Replace the fuse with a known good one. Check all the fuses as you can have more than 1 bad one. Good hunting-
o Alternator output voltage-if below 12v, pull and replace the voltage regulator/brushes(Bosch OEM buy online for $35, easy DIY) Retest voltage output
o If alternator checks out ok when you first test voltage output, the next thing I'd do is, with the ignition key OFF, and a voltmeter, start pulling fuses one-at-a-time and check voltage...it should read 0. If you get a voltage reading, then you have an open loop current draw on the battery. Replace the fuse with a known good one. Check all the fuses as you can have more than 1 bad one. Good hunting-
