1975 450 SLC - Died on me while I was driving home. Tried to restart, but dead battery. When I jump start the car, it fires right up and runs great until I disconnect the jumper cables, then sputters and dies.

I pulled the alternator and had it tested. the shop said it was good. The battery does hold a charge, so I'm guessing that the voltage regulator is the culprit.

Any ideas?? If so, WHERE IS IT? I can't seem to locate it, and the Hayes manual I've got doesn't specify the location.

Also, could it be another component?? THANKS!!

Very simple to test. Simply put a DC voltmeter across the battery. It should read in the area of about 13.5 to 14.5 volts with engine running. If it does not, I THINK your alternator will except an integral voltage regulator in place of the brush holder. You can get these for about $14 by clicking on FastLane above and then click on online catalog. I THINK that one for a 77 to 85 240D or 300D will fit in place of the brush holder on your alternator.

This will do away with the fenderwell mounted regulator. Do some research by seeing what belongs on your car first.

Good luck,

A quick and easy to use method when deterring a charging problem is to watch/notice the "battery" light. Ignition key to the #2 position (KOEO-key on engine off) battery light should be lit.

If it is not lit then ground the blue wire at the alternator, light should come on. If it lights up then you will need an Alternator (diode is open)

If the light is dimly lit while driving then you may get away with a replacement regulator. On your engine my information shows it is an integral part of the alternator, if so look at the armature when the reg is removed. If it is grooved replace the entire assembly.

I noticed yesterday that the BATT light was lit when I first turned the key to KOEO. After the car was jump started and died after the cables were removed, the light never came on after that. Bad ground or connection to blue alt wire?

Try jump staring the vehicle again, once started leave it connected to the other vehicle (TURN THAT VEHICLE OFF). Monitor your battery light...........you may see it dimly lit. If that is the case then a regulator may cure the immediate problem, however you need to investigate the armature prior to making that commitment. If it is deeply worn than an Alternator is a better choice.

If the light is not dimmly lit while running than your battery may be the suspect.