I have searched the archives for information on the alternator problem that I am having with my '86 420SEL but have not figured out what is wrong. The symptoms are that immediately after starting, the voltage at the battery is over 13.5 volts. Turning on the A/C it remains at 13.4 even at idle. Within a few minutes it drops to about 11.5 volts with A/C on and then off. I jumpered the ground from the engine to the battery neg. terminal with no change so the ground strap is OK. The battery light on the dash does not come on while the engine is running even when the voltage is low. It does light when the key is on but goes off when the engine starts. I took the alternator off and had it checked at a local parts place. It was charging but that agrees with what I find - when cold it charges.
I guess the question is if the alternator is bad or the voltage regulator. The other question is why doesn't the indicator light show that battery is discharging? I would appreciate any suggestions and response from anyone who has had similar problems.