best source underhood for keyed aux. power??? - PeachParts Mercedes-Benz Forum

coachgeo · #1 09-19-2010, 04:59 PM

I did search first. All I found was Aux. Fan mods.

1985 300SD

I need a switched power source by ignition key to run 12v fuel pump installed back at tank. Is there a 12v soure of power back near tank/trunk orr?? If not that.. under hood source?

Right now I have a cheap switch hidden under hood, wrapped in a plastic bag. It is actually reachable with hood closed. It does work as an Anti-theft device LOL.

Anyway... this back up car is loaned to a carless friend right now. He may buy it from me so we are thinking of rewiring what was orginally planed to be temporary solution to an air leaking pump into a more permanent solution cause it works great.

Where do you suggest?

Yak · #2 09-19-2010, 07:00 PM

My advice for running a pump would be to get a dedicated line from the battery with a fuse. Connect that line to a relay that is triggered by the ignition, like maybe the aux fan power supply?

Junkman · #3 09-19-2010, 07:30 PM

What are you going to do about making the pump stop if you're in a crash? Having diesel continuing to pump while the MBZ burns wouldn't be a pretty sight.

vstech · #4 09-19-2010, 08:40 PM

factory diesel electric pumps are fed through an oil pressure switch, if the engine dies, the pump dies. (chevy trucks for example...)
why would the "MBZ burns" is the accident likely to burst into flames? did the crash fly into someones' barbq grille? were boyscouts running a campfire in the road?
crashes resulting in fire are pretty unlikely. doubly so when the vehicle is a diesel powered auto!

however, wasting precious diesel fuel in the event of a crash does sound like a valid prevention service!

coachgeo · #5 09-19-2010, 09:05 PM

Quote:

Originally Posted by Yak

My advice for running a pump would be to get a dedicated line from the battery with a fuse. Connect that line to a relay that is triggered by the ignition, like maybe the aux fan power supply?

battery direct to pump......CHECK
Inline fuse

..................NEEDS ONE
Relay.............................Relay need a relay for a pump??? Didn't think it was that much draw??

Triggered by ignition- Tis the very question I am asking in this thread.

Anyone know if Yak's idea of Aux. Fan is a good source?

coachgeo · #6 09-19-2010, 09:11 PM

Quote:

Originally Posted by vstech

factory diesel electric pumps are fed through an oil pressure switch, if the engine dies, the pump dies. (chevy trucks for example...)
why would the "MBZ burns"...crashes resulting in fire are pretty unlikely. doubly so when the vehicle is a diesel powered auto!

hmmmmm.... well there goes that idea. Thought was increase the insurance.... call it a restored classic and let it burn after a fender bender (and a lighter conviently wired to stay lit)

Quote:

however, wasting precious diesel fuel in the event of a crash does sound like a valid prevention service!

except that a fuel pressure switch and my install time would cost more than the value of this old clunker at this moment and time.

So back to question.... Ignition key triggered power source? and now also Relay neccissary?

sixto · #7 09-19-2010, 09:42 PM

The overboost switchover valve gets switched power from fuse 10.

If you don't mind having the antenna up when the radio's off, use the black/white wire from the antenna switch to the antenna motor to send switched power from the radio or cigarette lighter (fuse 9) to the trunk. You might hear pump motor hum through the radio, though.

The problem with spilling Diesel fuel is it doesn't evaporate so lanes are shut down until the spill is cleaned up.

Sixto
87 300D

coachgeo · #8 09-20-2010, 12:52 AM

Quote:

Originally Posted by sixto

The overboost switchover valve gets switched power from fuse 10.

If you don't mind having the antenna up when the radio's off, use the black/white wire from the antenna switch to the antenna motor to send switched power from the radio or cigarette lighter (fuse 9) to the trunk. You might hear pump motor hum through the radio, though.

The problem with spilling Diesel fuel is it doesn't evaporate so lanes are shut down until the spill is cleaned up.

Sixto
87 300D

First to Yak..... Ok..... so I have to admit I'm stupid. I see your idea now. POWER from battery direct to pump that is interruped by a relay (switch) Circut connects by powering the relay from something switched of the Ign. Key, to complete the circut.

Sixto... BINGO- Power antenna does not work. Motor works... antena FUBARED and now broke off. Soooooo that will become the new power source.... maybe direct.. maybe via relay/direct to battery as Yak suggest.

Sixto? any suggestions on where to get power up thru into the truck from underneath?

Hobbs switche/relay which works off Oil pressure are not to horribly expensive but dont think I will go that route... least not at this point. A manual kill switch somewhere would be good though. ahhhhhh ha..... and that would bring back to anti-theft mode too LOL

JimmyL · #9 09-20-2010, 01:36 AM

Just properly fix whatever the problem is........

sixto · #10 09-21-2010, 12:02 AM

Quote:

Originally Posted by coachgeo

Sixto? any suggestions on where to get power up thru into the truck from underneath?

No need to go underneath. Run a wire through the firewall, under the door sills, up behind the rear seat back into the trunk.

Sixto
87 300D

babyjames · #11 09-21-2010, 12:11 AM

Isn't that the little one from the alternator? Tap into that, run it to your relay. You shouldn't need the lift pump at startup, right? The minute the alt. starts turning, you've got juice. The alt. stops turning - nightmare crash scenario - no pumpy.

I've got my electric fuel preheater wired this way. Works like a charm....

Jay.

coachgeo · #12 09-21-2010, 01:36 AM

Quote:

Originally Posted by sixto

No need to go underneath. Run a wire through the firewall, under the door sills, up behind the rear seat back into the trunk.

Sixto
87 300D

that's a shiat load of wire. Run all the way thru the front just to turn around and run it all the way back again.

Where thru the fire wall? One of the looms thru the wall, a steering shaft orrr?? you reccomend? For an 85 I got still a pretty good sound/heat sheld on the engine bay firewall so all the potential access points to go thru fire wall are hidden.

coachgeo · #13 09-21-2010, 01:42 AM

Quote:

Originally Posted by babyjames

Isn't that the little one from the alternator?

Isn't what the little one?

Quote:

You shouldn't need the lift pump at startup, right?

welllll..... was having lots of problems at start up and I suspected a bit of it was air leaks. Twas the whole reason for a by the tank install of pump. Thought was pump that far back pushing fuel will begin to show leaks of fuel in places that under OEM plumbing would be air leaks. Would help me to diagnose problems. Tis why the mention of this pump orginally intended to be only being temporary.

Quote:

.... The alt. stops turning - nightmare crash scenario - no pumpy...

good point.

sixto · #14 09-21-2010, 01:47 AM

A wire will be better protected running through the cabin than under the car.

There are a number of unused grommets by the brake booster. Or sneak it beside one of the wire bundles from the fuse box to the dash.

Sixto
87 300D

coachgeo · #15 09-21-2010, 09:42 AM

Quote:

Originally Posted by sixto

A wire will be better protected running through the cabin than under the car.

There are a number of unused grommets by the brake booster. Or sneak it beside one of the wire bundles from the fuse box to the dash.

Sixto
87 300D

???? Im guessing we are miscommunicating somewhere.

We agree--- best to not have wire running under car.

The pump is NOT mounted under the hood. It is mounted right under the fuel tank. Only way to get to the engine bay firewall that I know of is to run it under the car

The orginal question looking for a way to get it into the trunk to get powered from the Antena power source, was to avoid the present set up of running it up to the engine bay under the car again.

Thread Tools
Show Printable Version Email this Page
Display Modes
Linear Mode Switch to Hybrid Mode Switch to Threaded Mode