Friday night and let me post what has happened.
Replaced both battery cables. both wires from the alternator to the starter terminal.
Voltage now 12.8 engine off. 12.8 engine at idle. but at 1000RPM 13.4 volts and 13.5 at higher RPM's. Soit seems that the wires goin from the alternator to the startet terminal were old and building resistance. OR the battery ground was a problem. The battery positive seemed to be OK, checked the votage at the battery positive post and the starter eliminating the cable and the readings were the same.
It could also have been the battery grounding point on the chassis, I did clean it prior to attaching the new cable.

Dave

__________________
1970 220D, owned 1980-1990
1980 240D, owned 1990-1992
1982 300TD, owned 1992-1993
1986 300SDL, owned 1993-2004
1999 E300, owned 1999-2003
1982 300TD, 213,880mi, owned since Nov 18, 1991- Aug 4, 2010 SOLD
1988 560SL, 100,000mi, owned since 1995
1965 Mustang Fastback Mileage Unknown(My sons)
1983 240D, 176,000mi (My daughers) owned since 2004
2007 Honda Accord EX-L I4 auto, the new daily driver
1985 300D 264,000mi Son's new daily driver.(sold)
2008 Hyundai Tiberon. Daughters new car

Hey Dave,

I'm just perusing because I can't sleep due to a bad stomach tonight.

But, in thinking about the "bad" cable from the alternator to the starter terminal, I do not see how it could provide enough resistance to drop the voltage as much as you have noted. The reason for this is the fact that the cable is designed for something like 65 amps. With a new battery and very little load on, the alternator output is probably less than 5 amps. So, could this cable be damaged to the point where it would show resistance at an output of 5 amps? Seems to be impossible. If it were true, it would probably melt if you sent 65 amps through it with everything running.

It seems to be far more likely that the ground connection from the battery must have had resistance at its end in some way. Cleaning this would have cleared this issue and the voltage would have returned to normal.

I've been going through the same exact same low voltages as you have with yours. I have a 1982 300 Turbo. I found that the Glo-plug relay timer is not kicking off. I unplugged the relay after some deep head scratching and three used altenators last known to be good. Now my voltages are up to 13.4 at 1000 RPM just like yours. Wiring goes to a junction on the right fender near the battery. The wiring just felt warm while running and that was my clue. Tomorrow I'll see if I can find out what up with the glo-plug timer.

Great post by the way. I checked my ground wire on the body near the battery and there was some ugly stuff in the bolt threads. Cleaned it up and put some anti-corrosion goop on.

__________________
1984 280SEL, 62,000 miles
Euro model in the USA
1983 300D (Totaled out 10/2004)
New Factory Mint Green paint
Palomino int
1982 240D (Steak dinner for two)

My 3 yr. old Bosch AL166X reads 14.3 at idle first thing in the a.m. This is what it read brand new.

Reads 13.6 - 13.7 idling and fully warmed up after a 30 - 40 mile drive.

Good luck with the O'Reilley parts.

__________________
Mike Murrell
1991 300-SEL - Model 126
M103 - SOHC
"Fräulein"

FineOlBenz

.... Steak dinner for two? ------> !!!

Jl

two observations guys.first the reading at idle will definately be influenced by the size of the battery[bigger means lower reading] secondly don't overlook the main ground at the bellhousing from engine to chassis [unless you have a separate ground running from alternator to chassis].

__________________
David S Poole
European Performance
Dallas, TX
4696880422

"Fortune favors the prepared mind"
1987 Mercedes Benz 420SEL
1988 Mercedes Benz 300TE (With new evaporator)
2000 Mercedes Benz C280
http://www.w108.org/gallery/albums/A...1159.thumb.jpg

Steak dinner for two is what I paid for the car. It was not running. I bought another 240 hit in the rear for $50 and swapped out engine and trans. Just got it running and the hulk of the wreck sent to the crusher and my new (clumbsy as she puts it) totaled out a real nice 300 Turbo. And within hours asks "Dad is the blue one ready for us to drive??"

Doesen't everyone have a daughter-inlaw like mine?

By the way I replaced the glo-plug timer and she's at 13.75 volts and the glo-plug lamp on the dash works now.

__________________
1984 280SEL, 62,000 miles
Euro model in the USA
1983 300D (Totaled out 10/2004)
New Factory Mint Green paint
Palomino int
1982 240D (Steak dinner for two)

Awesome!

Jl

Sounds like my problem with my old diesel GMC van. Even though the belts looked good and felt tight it wasn't until I replaced them that my problems disappeared.