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#1
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What's most convenient 12v source in engine compartment?
Immediate need is to test the ELR actuator on an 87 300TD. But, in general, what's the most convenient place in the engine compartment to tap into a 12v source?
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14 E250 Bluetec "Sinclair", Palladium Silver on Black, 153k miles 06 E320 CDI "Rutherford", Black on Tan, 171k mi, Stage 1 tune, tuned TCU 91 300D "Otis", Smoke Silver, 142k mi, wastegate conversion 19 Honda CR-V EX 61k mi Fourteen other MB's owned and sold 1961 Very Tolerant Wife |
#2
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This sounds like a trick question, but 'll bite. How about the battery?
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2009 E320 Bluetec 117,000 1995 E300D 306,000 Sold 1996 Ford Taurus LX 130,000 Sold 1985 300TD Still 225,000 Sold 2016 Ford Fusion 24,900 |
#3
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Yes, sometimes we over think stuff to the extent that we are oblivious to the obvious solution.
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84 300D, 82 Volvo 244Gl Diesel |
#4
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No, not a trick question. I just thought there might be easier sources....or switchable sources, for that matter....that could come in handy.
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14 E250 Bluetec "Sinclair", Palladium Silver on Black, 153k miles 06 E320 CDI "Rutherford", Black on Tan, 171k mi, Stage 1 tune, tuned TCU 91 300D "Otis", Smoke Silver, 142k mi, wastegate conversion 19 Honda CR-V EX 61k mi Fourteen other MB's owned and sold 1961 Very Tolerant Wife |
#5
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I took a quick look at the schematic for a W124 and you are right, there is no easy way to grab a protected +12 V dc for testing under the hood. The load side of the fuses are all recessed on the 124 fuse box so that's out.
IMO it is way too dangerous to have an unfused test lead straight from the battery flopping around the engine compartment. I would rig up a test lead with a small in-line fuse holder and go off the battery +. If your test lead is made with small wire (like #18 or #20) then I would go no more than 3-5 amps max on the fuse. If you are testing electronic inputs then go with a 0.5 or 1 amp fast blow fuse max. That way if you miss the pin you have a fighting chance of not smoking something, and if it hits the frame it will be a little sparky sparky and crackle before the fuse opens. If you are testing solenoid actuators you will need the 3-5 amps slow blow and maybe more. If so you will need to step up to #12 or #14 wire and up to a 10-15 A fuse maximum. But I would only do that if you need more current for your test. That size of fuse will allow a big bang before it clears if you hit the frame, and it will smoke electronics if it is hooked to the wrong point. One last thing - some actuators do not like having 12 Vdc directly applied to them, they operate off a reduced voltage from the electronics. And sometimes the driving circuit in the electronics does not like having 12 V dc applied externally to the output from a foreign source. Just be careful, I would hate to see you smoke something.
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The OM 642/722.9 powered family Still going strong 2014 ML350 Bluetec (wife's DD) 2013 E350 Bluetec (my DD) both my kids cars went to junkyard in 2023 2008 ML320 CDI (Older son’s DD) fatal transmission failure, water soaked/fried rear SAM, numerous other issues, just too far gone to save (165k miles) 2008 E320 Bluetec (Younger son's DD) injector failed open and diluted oil with diesel, spun main bearings (240k miles) 1998 E300DT sold to TimFreeh 1987 300TD sold to vstech |
#6
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Fuses
Mercedes has used a number of add-on fuses over the years, such as the 30A strip fuse for the climate control blower. Another fuse was added sometime in the 1990s for the cellphone. The picture shows the cellphone fuse for my 1995 E300; since I have no cellphone, I adapted it for a cabin power outlet. In the picture you can also see a dual fuse holder (got it from a junkyard BMW) that I added for use of a battery trickle charger. These fuse holders are inexpensively available in auto junkyards. Look near the battery or near the regular fuse box or panel.
Jeremy
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"Buster" in the '95 Our all-Diesel family 1996 E300D (W210) . .338,000 miles Wife's car 2005 E320 CDI . . 113,000 miles My car Santa Rosa population 176,762 (2022) Total. . . . . . . . . . . . 627,762 "Oh lord won't you buy me a Mercedes Benz." -- Janis Joplin, October 1, 1970 |
#7
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There's the downstream end of the 80-amp fuse in the glow relay.
Sixto 87 300D |
#8
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Source of +12V
Which is hot at all times, I believe.
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"Buster" in the '95 Our all-Diesel family 1996 E300D (W210) . .338,000 miles Wife's car 2005 E320 CDI . . 113,000 miles My car Santa Rosa population 176,762 (2022) Total. . . . . . . . . . . . 627,762 "Oh lord won't you buy me a Mercedes Benz." -- Janis Joplin, October 1, 1970 |
#9
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You could make test lights out of flimsy wire and 12v leds from radio shack. Push a straight pin through the wire insulation and solder the wire to the pin. When you're done, pull out the pin and the insulation should close up.
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2009 E320 Bluetec 117,000 1995 E300D 306,000 Sold 1996 Ford Taurus LX 130,000 Sold 1985 300TD Still 225,000 Sold 2016 Ford Fusion 24,900 |
#10
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If there is nothing around - a regular 5A spade fuse, two female spade connectors some electric tape and a test lamp is all you need to modify a test lead
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2012 BMW X5 (Beef + Granite suspension model) 1995 E300D - The original humming machine (consumed by Flood 2017) 2000 E320 - The evolution (consumed by flood 2017) |
#11
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Hmm I think the feed to the aux fan is a good source... and it's switched with the key off a relay.
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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 190D 2.5Turbo 1987 190D 2.5-5SPEED!!! 1987 300TD 1987 300TD 1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere! |
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