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Old 11-11-2004, 05:38 PM
Registered User
Join Date: Jul 2003
Location: Mountain View , Calif
Posts: 6
What instrument lights...and charging

should come on when I turn the key on? All I get is the glow plug light, which cycles normally(I think)

Also, I have a new(rebuilt) alternator that at idle only shows 12.25 volts on a good voltmeter. I searched and I see where that should be 14.4 volts, right. Battery is also new.
I'm going to clean the alt connector next. One post said to ground alt to body, is that an external ground?
PO really had the wiring screwed up and I'm trying to sort it out. No wipers, but whunter said I could run a fused jumper for now.

I have 2 color fuses, red and white, which amps is which? does someone have a sketch/diagram of the fuse box which shows the different amps?

I have always wanted a diesel MB and after some initial discouragement, I've almost got her on the road.

This is an 80 300D, unknown miles(at least 184,000), unknown history.

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Old 11-11-2004, 05:52 PM
The Warden's Avatar
Certified diesel nut
Join Date: Mar 2002
Location: Pacifica (SF Bay Area), CA
Posts: 2,946

At least on my car, when the key is first turned on, the alternator, brake pad warning light, and the brake warning light come on. I think the seat belt light's supposed to come on too, but a p/o disconnected that system on my car. Once the engine's started, the lights should go off (except the brake warning light if your parking brake's set)...although, on some cold days, the lights have stayed on with the engine running until I rev it...I think those lights go off when the alternator's putting out enough voltage, which may not be happening if the RPM's are that low.

What is the alternator putting out at a higher RPM than idle? I wouldn't call it likely, but the alt. may be putting out more juice at higher RPM's than at idle...especially if your idle may be set low (should be 750 RPM's IIRC).

Dumb question, but was the voltage regulator/brush assembly replaced along with the alternator, or was the old one re-used?

On the fuses, there's actually supposed to be a few blue fuses in there as well. I think that white is 8 amp, red 16 amp, and blue 25 amp, but the numbers may be off...but they definitely go in that order from weakest to strongest. Blue's for things like the blower motor. As for a diagram, I'm guessing that the fuse box cover's gone, or the printout contained therein is gone. I'm at school right now, but if no one's posted a diagram before I get home, I can scan in my printout...since my car's a different year, some things may be slightly different, but it should give you a place to start out from.

Hope that helps a little bit...good luck! BTW, hi! Didn't realize you had registered on here...
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Old 11-11-2004, 09:29 PM
Registered User
Join Date: Jul 2003
Location: Mountain View , Calif
Posts: 6
Fuse cover gone....DUH!!!

Ok, I found the diagram. Thanks. I have no blue fuses at all, all my reds are plastic and whites are ceramic.
Something is draining my battery, I think.
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Old 11-11-2004, 09:35 PM
Registered User
Join Date: Aug 2001
Location: Evansville, Indiana
Posts: 8,150
The battery drain is probably the reason for the "rewiring" job -- very poorly done, I'm sure.

The way to find the "leak" is to connect a test lamp between the positive battery cable and the positive post. If the lamp lights, you have a drain large enough to cause trouble.

Do the same thing while removing and replacing fuses one at a time -- when the lamp goes out, you've got the circuit and can go from there.

Things no one thinks of are trunk lights staying on (either climb into the trunk and have someone close it, or pull the lamp -- safer!) or the glove box light staying on because the switch is mis-adjusted. Pull the bulb on that one to check.

You can also have a stuck switch somewhere or an aftermarket radio amp that stays on all the time, too.

A high resistance ground on the "hot" side of the fuse box is also possible if none of the fused circuits is the problem.

1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!
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