How To: Wire a Bosch Pump for Your Aftercooler

[PainIs4ThaWeak]

*Before you get started:

Jose indicates that the pigtail for the pump has 16AWG wire on it. For the sake of ease, might as well use 16AWG wire for all your connections (unless someone sees an issue with this - correct me, if you do.)

A relay will be needed to wire this safely. An SPST (Single Pole, Single Throw) or SPDT (Single Pole, Dual Throw) relay can be used.
Members have mentioned that they haven't had any reliability issues using the following relays:
Hella SPST:

Amazon

Amazon

Hella SPDT:

Amazon

Amazon

It is recommended to wire in a fuse in between the relay and the battery, for which, something like this can be used:

Amazon.com: In-line ACT Water-resistant Fuse Holder - 10 AWG: Automotive

Amazon.com: In-line ACT Water-resistant Fuse Holder - 10 AWG: Automotive

(Anyone know what amperage fuse should be used?)

For wiring the relay, you can use something like this (I'm sure there are nicer options than this around) :

Amazon.com: Absolute SRS105 5-Pin 12 VDC Relay Socket Interlocking Style: Automotive

Amazon.com: Absolute SRS105 5-Pin 12 VDC Relay Socket Interlocking Style: Automotive

IF YOU DESIRE TO USE A SPST SWITCH, something like this could be used:

Medium Duty Toggle Switch SPST 10 Amp : Amazon.com : Automotive

Medium Duty Toggle Switch SPST 10 Amp : Amazon.com : Automotive

(If you want to use an SPDT switch, you'll have to consult the documentation below, under "Sources".)

To wire the aftercooler pump:

A. Starting from the Postive (+) battery terminal:
1. Connect one end of 16AWG wire to battery (by means of a spade/loop connector or whatever works for your situation)
2. Opposite end of this wire attaches to one end of the in-line fuse holder
3. Opposite end of the in-line fuse holder goes to Pin #30 on the relay (i.e. - whatever color lead from the relay harness that matches up with pin #30)

B. Starting from Relay Pin #87:
1. Connect one end of 16AWG wire to lead for Pin #87
2. Connect opposite end of 16AWG wire to Positive (+) lead of Bosch pump
3. Connect Negative (-) lead of Bosch pump to any available ground.

C. Starting from Relay Pin #85
1. Connect one end of 16AWG wire to lead for Pin #85
2. Connect opposite end of 16AWG wire to ground (Negative (-) battery terminal is probably the best place for this)

D. Starting from Relay Pin #86 (This is the pin used to wire in a switch, if you desire)
D-1. TO WIRE WITHOUT A SWITCH:
1. Connect one end of 16AWG wire to lead for Pin #86
2. Connect opposite end of 16AWG wire to a switched power source (Positive (+) lead.) This will allow the pump to turn on when the car is started. This "switched" power source can be: the power windows lead, the car's ignition lead, the fuel pump lead, etc. (Consult a Honda FG/FA service manual for locations of these "switched" power leads.)
Where you DON'T want to wire this: radio lead, headlight/foglight lead, interior light lead, or any other source that can be turned off while the car is running.

D-2. TO WIRE *WITH* A SWITCH: (This will allow the pump to be turned on/off, as desired, by the manipulation of said switch.)
1. Connect one end of 16AWG wire to lead for Pin #86
2. Connect opposite end of 16AWG wire to one of the connections on the SPST switch (I believe they are interchangable - someone correct me if I'm wrong)
3. Connect one end of 16AWG wire to the other connector on the switch.
4. Connect the opposite end of the 16AWG wire (mentioned in step 3) to a switched power source (Positive (+) lead.) This will allow the pump to turn on when the switch is turned to the "ON" position. This "switched" power souce can be, as was mentioned earlier, the power windows lead, the car's ignition lead, the fuel pump lead, etc. (Consult a Honda FG/FA service manual for locations of these "switched" power leads.)
Where you DON'T want to wire this: radio lead, headlight/foglight lead, interior light lead, or any other source that can be turned off while the car is running.

NOTE: If you're using an SPDT relay, Pin #87A is unused.

I believe that should do it - Again, any input is appreciated.

Sources:

How to Wire a Mini Toggle Switch | eHow.com
Using Relays To Wiring Off Road Lights And Accessories
Switches
Wiring a Relay for Accessories
FAQ: RELAYS; how they work and how to wire it up...

[Honda_guy58]

Good info! I wired my pump with no relay. Should I consider adding one?

[mercurysunshine]

well this is useful.. thanks

[PainIs4ThaWeak]

Originally Posted by Honda_guy58

Good info! I wired my pump with no relay. Should I consider adding one?

Anytime a "large" power draw is called by an accessory, it is recommended to use a relay.

What constitutes "large" is probably up to a matter of opinion, but it is a more "fire proof" option to incorporate a switch in higher-draw cases.

[jmercado567]

Thanks for this. Its been needed for a long time. Everyone will love you!!

[PainIs4ThaWeak]

No worries Jose.

Really need everyone to correct me on any aspects that are not correct though.

[mercurysunshine]

why is a relay needed again?

[mercurysunshine]

i dunno where the edit button went but i bought a relay but then i did the math and this pump only draws something like 1.8 - 2 amps.. i dont think that is a big enough draw to need a relay... correct me if im wrong... what it does need though is a switch in the cabin so you can keep the acc on and not kill the battery quick like

[PainIs4ThaWeak]

I'll have to dig up the data sheet again on the Bosch pumps. If its really only a 2 amp draw then I'd be inclined to agree with you Matt, that a relay probably isn't needed.
But I'm not exactly an electrical engineer either, which is why I've been asking for input from the electrically smart people.

[PainIs4ThaWeak]

Here is one version of the Bosch pump, with testing done by Merc and Hondata: Tech - Supercharger Intercooling

According to them, it looks like the 002 pump pulled up to ~4.25amps @ 13v?

[mucter]

It's not always about how much amperage it draws when it's working fine. It's about what happens when it fails. It's pretty common for electrical items to short out and draw large amounts of current when they fail. Hence why there's always a fuse involved...

What you don't always know is, will the source for 12v switched on the car be able to handle the load that could be drawn when your device shorts. A relay eliminates this concern entirely by only using the 12v switched as a signal wire. This way you never have to worry about damaging anything in the stock wiring on the car.

[mercurysunshine]

Amps = Watts / Volts .. so you have 20W / 12V = 1.6666A or 25 w i cant remember

[mercurysunshine]

Originally Posted by mucter

It's not always about how much amperage it draws when it's working fine. It's about what happens when it fails. It's pretty common for electrical items to short out and draw large amounts of current when they fail. Hence why there's always a fuse involved...

What you don't always know is, will the source for 12v switched on the car be able to handle the load that could be drawn when your device shorts. A relay eliminates this concern entirely by only using the 12v switched as a signal wire. This way you never have to worry about damaging anything in the stock wiring on the car.

isnt that why you would put, say, a 3amp fuse in line with it? We know the stock wiring harnes can handle 3 amps.

[mucter]

You need to give it breathing room.

[mercurysunshine]

whats that mean?

[PainIs4ThaWeak]

For voltage fluctuations, I believe is what Mucter is getting at.

[mucter]

yup yup

[PainIs4ThaWeak]

But I think what Matt is attempting to say is:

Why would we need to worry about voltage fluctuations that produce more than a 3 amp draw (e.g. a catastrophic pump failure), when all that would happen (if using an add-a-circuit) is having the 3 amp fuse blow?

Or is there something I'm missing?

[mucter]

I doubt the pump draws only X amps. I'm sure it varies based on load. And the load will depend on a variety of factors, the biggest of which is likely the volume of water it's pushing around in the system. And we have different systems, with different cores, different HX's, different lengths of hose, etc. I don't think there's nearly enough data to know that the pumps only ever draw X amps...

Pumps are always like this, volume/flow determines load and thus duty. With something like that, better safe than sorry imo.

[PainIs4ThaWeak]

But ofc, I agree that any electronic device will never pull a completely static voltage/amperage/wattage.

For those that aren't aware, even the length and gauge (AWG) of the wire used will affect the V/A/W of the device being powered. For example, a 15ft run of 16AWG copper wire will see ~3% drop in voltage at the device. On a 12V DC system, that would be about 11.625V DC.

I understand a small amount of electrical principles, but not enough to be "smart".

This discussion has taken me from "yea, its a good idea to use a relay", to "no, it's not needed", and now to "I think I'm going to use one anyway."

Thanks for the input Jay.