If they checked the alternator while afterglow was running, it could look that way. Your report of approx 14 volts at idle suggests otherwise.

Yeah, if I can get 14 at idle, I don't need a new alternator. It was typical autozoo tech who was just telling me what the computer said.


The car starts every morning if I start and run it every day. If I leave it for two days (which I am doing now) It usually won't start. I have dropped the "car off" amp draw down to .13 amps. I have now left it for two days and I'm going to see what my battery volts are after two days and then see if it cranks. If I try to start it tomorrow morning and it doesn't start...its straight to autozoo for a new battery (hopefully a nice warranty covered battery).

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77' 300D, "Cartman" SOLD @ 150K (didn't know what I had)
83' 300SD, "The Superdon" 325k+ @ 28mpg
95 E320 wagon, "Millennium Falcon" 231k+ @ 24 Mpg
95 E300D, "Sherley" 308k @ 33.69 Mpg, currently anticipating a head
99 Suzuki Intruder "Trudy" @ 45 mpg

0.13 amp draw with the key off is too much and part of the problem. Start pulling fuses and see which circuit it is.

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85 300D turbo pristine w 157k when purchased 167,870 July 2025
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

HA! it was a .58 originally. At this point it has to be my Sony Xplod Bluetooth radio. I've been considering installing that into my 95. Looks like thats what I'll be doing.

I checked the voltage on the battery. 12.00 even...wait...12.05 after sitting for a day and a half. I don't like that either. I'll do another test with the old sony tape deck installed after I check it's off amp draw.


So.....if I lose two glow plugs will my indicator light still light up?

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77' 300D, "Cartman" SOLD @ 150K (didn't know what I had)
83' 300SD, "The Superdon" 325k+ @ 28mpg
95 E320 wagon, "Millennium Falcon" 231k+ @ 24 Mpg
95 E300D, "Sherley" 308k @ 33.69 Mpg, currently anticipating a head
99 Suzuki Intruder "Trudy" @ 45 mpg

it depends on which plugs fail... but the answer is maybe.

I'd love to be one of the TWUTGPR members... but it's best to just notice it's on or not in the morning, and listen for the relay to click when it's cold. if it does not come on, check your glow plugs.

Thayer...
have you tried starting it while measuring the voltage, and then unplugging the glow plug harness from the relay and checking if the voltage INSTANTLY jumps to 14?

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John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread
"as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do!

My drivers:
1987 190D 2.5Turbo
1987 560SL convertible
1987 190D 2.5-5SPEED!!!

1987 300TD
2005 Dodge Sprinter 2500 158"WB
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!

Why would it matter which two plugs failed?

Because the glow plug light being on is controlled in part by a circuit that compares the current draw on a few of the glow plug pins in the relay.
Certain combinations can still light the lamp, while others won't.

If I remember what I read a while back, cylinder 1 is compared to the rest, but I don't know the actual ins and outs beyond that.

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-Josh
Testing the cheap Mercedes axiom, one bolt at a time...