930 fuel pump relay wiring - once and for all

[sand_man]

One of the only times my 930 ever left me stranded was due to the infamous single fuel pump fuse..luckily I figured it out and got it home. Obviously we're asking a lot of this fuse. In my case, the fuel pump wiring to the fuse panel where this fuse sits was cracked and overheated. I installed a more modern blade style fuse holder, wired in the same place...still just holding a single fuse. Thus far it's worked fine, but I've always had intentions of doing the "Lee Rice dual fuse mod"...just for good measure.

My only problem (well maybe not my only problem) is that while I'm good at the mechanical stuff, I ain't no Wile Coyote, Genious At Large, when it comes to electrical matters. In short (no pun intended), I don't find the Lee Rice instructions completely clear.

Here are the directions:

Fuel Pumps on 930 Turbo, 1977-1989, (1976 used a single pump)

Both fuel pumps take power from one fuse (#16). Install a two gang fuse block, Nr. 911.612.085.04, near main fuse strips and run a red 3.0 cm/2 red wire from the battery terminal directly to the new fuse terminal, at the two gang end. The two fuel pump relay sockets for pump #1 and #2 have a red wire 2.5 cm/2 running from fuse #16 to terminal #30 of pump #2 and then run over to terminal #30 of pump socket #1. Cut the wire running between the two pins, #30, and securely splice it by solder and good insulation to a new 3.0 cm/2 red wire, running it to the new fuse block at #2. Be sure to solder the wire end before installing it to the fuse block. Remove the red 2.5 cm/2 wire from fuse #16 and run it to the new fuse block and attach it to the #1 fused terminal. #2 fuse should be a blue 25 amp, as it will still power the warm-up devises as well as the #2 fuel pump. #1 fuse can be a red 16 amp fuse.

http://www.pelicanparts.com/techarticles/rice_ramblings/rice_ramblings-2.htm

I drew this low brow picture based on his description of the existing factory wiring:


What is unclear to me is the portion about "Cut the wire running between the two pins, #30, and securely splice it by solder and good insulation to a new 3.0 cm/2 red wire, running it to the new fuse block at #2." Does that mean that the two number 30 pins are spliced together then run to a new 3.0 cm/2 wire, or is each number 30 pin wired with it's own fuse?

Like this:


Or like this:

[sand_man]

Go easy on me, the pictures above are not meant to be representations of the factory wiring diagram...just high-level simplifications.

[timc]

each 30 pin wire from each of the FP relays goes to it's own fuse (in the new fuse block), as in your last diagram. The old 16 wire from the old fuse block to the 30 pin on one of the relays is no longer needed, and should be removed. At least this is what the "Rice" diagram is showing.

[sand_man]

Gotcha...I think I've got it now. I'll post another drawing that's a little more clear. Thanks!

[rsrfan]

Originally Posted by timc

each 30 Pin Wire From Each Of The Fp Relays Goes To It's Own Fuse (in The New Fuse Block), As In Your Last Diagram. The Old 16 Wire From The Old Fuse Block To The 30 Pin On One Of The Relays Is No Longer Needed, And Should Be Removed. At Least This Is What The "rice" Diagram Is Showing.

+1

[356-930]

Originally Posted by sand_man

Or like this:

This drawing is correct. To clean it of confusion, delete the verbiage "wire from #16 fuse" and the wire/pigtail leading to it.

[targa todd]

Sounds like a great little project. Our host doesn't seem to carry the fuse block referenced by part number. Has anyone had any luck sourcing this?

[Akila]

How about something like this..........

[hobieboy]

Sandman,
As many said already, your last diagram is the correct one.
One big issue is the original wire from the fuse panel to the 1st relay. That wire is too thin to carry current for both relays.
When you implement the last diagram, make sure you use a large diameter wire from your new fuse panel to the battery too.

[nocarrier]

Looks good to me too.

You can get away with the number 16 wire from the old fuse block.

On the relay pin 30 comes from the battery and when energized across pins 85 and 86; connect pin 30 to pin 87 providing a path to the positive terminal on the fuel pump.

Just for reference, when the relay is not energized pin 87a and pin 30 are providing a path (normally closed). Pin 30 and pin 87 are normally open.

I actually opened up one of the fuel pump relays today because my rear one was sticking. I also found inside a transient noise surpressor (sp) diode. With this diode, the relay is now polarity sensitive. Just a heads up in case anyone wanted to use a regular black relay in its place. The diode is there to basically deal with a short (sort of) from a device using a high resistance coil.

Here is a great calculator for determining which wire to use. You can enter the voltage, amps, gage and length of wire to calculate the voltage drop. To be safe you could always go one up on the size.

http://www.powerstream.com/Wire_Size.htm


Hope this helps!

-Adam

[sand_man]

Thanks for all the input, guys. It helps me to see it in pictures. And I think the bit in Lee Rice's directions about just using the wire going to #16 is another place I got confused and that's why I was still showing it on my diagram, as a random pig-tail...but I now understand how it could still be used.

Here is a slightly revised drawing:

[sand_man]

I've been saving this question for last. Even though I've been driving and working on "foreign cars" for years and have hardly any standard/'merican tools, I totally suck at the metric system! Blame it on my Catholic schooling!

So what exactly does 3.0 cm/2 and 2.5 cm/2 translate into gauge? I've got a few conversion websites bookmarked, but I just want to be sure that "new math" doesn't put the bad ju-ju on me

Now if you'll 'scuse me, the zoo-keeper is here with my bananas...

[nocarrier]

There is no exact conversion for 2.5 cm/2 or 3.0 cm/2.

However 2.5 cm (actually 2.5mm squared) is somewhere between 12 and 14 gauge. The /2 means two conductor it can be either a "zip" style wire (I wouldn't use) or two wires in a common outer shield. In other words, the first number is the gauge and the second number is the amount of wires in a group.

This wouldn't be my choice as when you buy wire with two or more conductors; the wires are different colors such as red and black in let's say a 14/2 reel of wire.

3.0cm/2 is pretty close to 12 gauge wire with 2 conductors as well.

-Adam

[NathanUK]

Adam, I think Lee Rice used the 2 to represent the 'square'.

Sand, I've read that mod many times and always got last half way through.

It's an easy mod though. A simpler way of looking at it is to run 2 new wires from the battery and have a fuse on each wire for just over half the amps that the stock fuse was. As for wire size I would use the same wire size that was stock even though we now are going to be drawing less current through them. This should work fine, if a fuse blew then I would try to find out if one pump has a higher load than the other, I'm guessing they are both equal.

Look at electrics like water, start at the battery, go through the device and back to the battery. You always want a fuse after the battery and before any hazards. You want the fuse as small as possible without it blowing for no reason. You just have to do the maths of wattage divided by volts = the amps.

Also, volts divided by ohms = amps. You can check ohms of a simple device like a bulb with it not being powered. For more complicated devices you can use a meter but you have to disconnect one connection and place the meter between the device and the wire. http://www.allaboutcircuits.com/vol_6/chpt_2/4.html

[nocarrier]

I had a funny feeling why the instructions called for 2.5cm squared.

Wouldn't that be a huge wire?

Maybe he meant 2.5mm squared?

Now I'm confused!

[sand_man]

Originally Posted by nocarrier

I had a funny feeling why the instructions called for 2.5cm squared.

Wouldn't that be a huge wire?

Maybe he meant 2.5mm squared?

Now I'm confused!

EXACTLY!!! I started doing some conversions and he was calling for some pretty thick-azz wires!!! Again, I didn't find these instructions very clear. So what gauge wires do you think?

[NathanUK]

Yikes, I didn't even notice that. I read it as 2.5mm2

[timc]

Originally Posted by NathanUK

and have a fuse on each wire for just over half the amps that the stock fuse was.

Why would you not use the same size fuse that was originally used in #16? Is it because you are now just supplying power to one FP with one source?

[timc]

The "Rice" notes also state that the # 2 fuse of the new fuse block should be a 25amp fuse as it will also provide power to the warm-up devices as well as the #2 fuel pump, but in the diagram, only pin 30 from the #2 FP relay goes to the #2 fuse. I'm guessing that the #2 FP relay also provides power to the warm-up devices.

If this is correct, then Nathan, I would not cut the amps in half for the second fuse, I'd use the orig spec of 25 amps. I guess on FP1 you could use 16 as the Rice diagram states.

[sand_man]

Originally Posted by timc

The "Rice" notes also state that the # 2 fuse of the new fuse block should be a 25amp fuse as will will also provide power to the warm-up devices as well as the #2 fuel pump, but in the diagram, only pin 30 from the #2 FP relay goes to the #2 fuse. I'm guessing that the #2 FP relay also provides power to the warm-up devices.

If this is correct, then Nathan, I would not cut the amps in half for the second fues, I'd use the oem of 25 amps, I guess on FP1 you could use 16 as the Rice diagram states.

And that brings me to question number 3!!!! Does Lee Rice have it right about which fuse in the "new" two gang fuse block gets the amperage ratings?