Hi guys,

The GENER light on my 72 w108 has started coming on at idle. It goes away when I hit the gas and after a little while of driving. Any thoughts?

Jose

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Current
1972 280SE 4.5 Dark Green, Cognac. Pics!
2014 Range Rover Sport Supercharged. Santorini Black, Dynamic Package, Front Climate Comfort and Visibility Package, Vision and Convenience Package.

Gone But Not Forgotten
2010 Explorer Limited, 2010 R350 4MATIC, 2011 Jeep Grand Cherokee Overland, 2009 Audi A4 Cabriolet, 2009 Ford Flex, 2008 Mercedes-Benz ML350, 2008 Mercedes-Benz E350, 2007 Mercedes-Benz C230, 2005 BMW X5.

First check the tension on the belt. Second, clean and inspect the battery cables, terminals and earthing points. Third, use a voltmeter to determine the voltage at idle and at a higher RPM (apx. 1500-2500).

Voltage on a "good" alternator should be appx. 13.7-14.2 VDC.

Amperes are the true test of an alternator's ability but the "idiot" lights are triggered by voltage readings.

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“Whatever story you're telling, it will be more interesting if, at the end you add, "and then everything burst into flames.”
― Brian P. Cleary, You Oughta Know By Now

Thanks Mike!

The battery is brand-spanking-new. So I know it's not that. I'm gonna check the belt and voltage.

j.

__________________
Current
1972 280SE 4.5 Dark Green, Cognac. Pics!
2014 Range Rover Sport Supercharged. Santorini Black, Dynamic Package, Front Climate Comfort and Visibility Package, Vision and Convenience Package.

Gone But Not Forgotten
2010 Explorer Limited, 2010 R350 4MATIC, 2011 Jeep Grand Cherokee Overland, 2009 Audi A4 Cabriolet, 2009 Ford Flex, 2008 Mercedes-Benz ML350, 2008 Mercedes-Benz E350, 2007 Mercedes-Benz C230, 2005 BMW X5.

Don't overlook cables and the earthing points. Inspect for a swelling INSIDE the plastic sheathing. This is a sign of hidden corrosion. The earth/ground connection between the battery and the body is also a commonly overlooked trouble area. Check the feed to the alternator.

80% or better of charging/starting problems are usually cable related.

__________________
“Whatever story you're telling, it will be more interesting if, at the end you add, "and then everything burst into flames.”
― Brian P. Cleary, You Oughta Know By Now

Use a multimeter with at least one clamp terminal. While running the engine, clamp on the battery negative post. Then measure voltage with the other terminal on areas like:

• The chassis where the negative terminal attaches
• The alternator housing
• The grounding point where the D-Jet harness attaches

Try these with the headlamps on, and with them off. You can also rev the engine during the tests as well.
Ideally, you would see no more than 0.02 volts on the first test, and 0.1-0.2 tops on the rest. If you measure anything more than that, your grounding points are likely bad.

This is of course after you check to make sure that the alternator is providing a good charge. The brushes are the most common wear point. Plenty of YouTube videos show how easy it actually is to rebuild an alternator on your own. I couldn't believe it myself, will likely only ever buy a replacement in the future if the windings / armature are actually shot, and even then, you can buy replacements for those too!

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Current:
2021 Charger Scat Pack Widebody "Sinabee"
2018 Durango R/T

Previous:
1972 280SE 4.5
2014 Jeep Grand Cherokee Limited "Hefe", 1992 Jeep Cherokee Laredo "Jeepy", 2006 Charger R/T "Hemi"
1999 Chrysler 300M - RIP @ 221k