bonecrrusher

Hello everyone - I am trying to wiring up my external fuel pump and have a hobbs switch activate it above 5 psi.

Car setup:
2005 C6 Corvette LS2 - with E-Force supercharger.

I have the Hobbs switch mounted to the 1/8" port on the drivers side of the blower.

I have a Bosch 5 wire relay with the following wire configuration:
30 - fused power source coming from Alternator
85 - Power wire to fuel pump
86 - Ground
87 - Trigger wire to Hobbs switch
87a - not used

Hobbs switch wiring - Metripack Pac66 - two wire model.
A) Ground wire
B) Trigger wire coming from #87 from relay.

Fuel Pump - power wire coming from #85 of relay.
Ground wire is ground to frame.

I've got power going into the relay - no issue there.
I driven the car around - and the supercharger is hitting 9 psi - but the switch/fuel pump is not activating.

Could I have the relay wired up wrong?

I have tried to switch the wires going into the Hobbs switch - and no difference.

I have switch the relay to an entire new relay / harness - and same result - switch/pump is not coming on.

bonecrrusher

More info on the Hobbs switch:

4-6 psi Honeywell Hobbs Switch with Metripack Connector, factory set at 5psi

Circuit: SPST Normally Open, Adjustable pressure
Diaphragm: Polyimide film
Temperature Range: -40° F to + 250° F
Connector: 1/8 -27 NPT male thread
Base: Plated Steel
Cover: Glass reinforced polyester

90zcrex

You have the relay and hobbs switch wired incorrectly.
relay needs to be...
86- run to switched battery voltage
85- run to Hobbs switch pin 1
30- run to battery voltage use larger gauge wire here for pump power.
87- run to fuel pump power side.

Hobbs switch
pin 1- to relay pin 85
pin 2- chassis ground

EnviedC6

90zcrex is correct. Above is a diagram of the relay and how it works. 85 and 86 are the coil pins of the relay. When the coil is energized, the internal switch throws closed to close pin 30 (pole common) to pin 87 (Normally Open Pole). You are using the hobbs switch to send back the ground side of the relay coil.

bonecrrusher

Thanks guys - I followed 90z's wiring directions - and got it working last night.

I took the car out last night - and the fuel pump kicked on above 5 psi.

I thought that I had done my research - I had looked up that Bosch 5 pin relay and thought I had it mapped out correctly. I guess don't trust every diagram that you see.

Question for you guys - where would you recommend tying into for the switched 12 volt source?

I was thinking a tap a fuse tied to a switched source inside the fuse box - unless there is a better source out there.

Thanks!

90zcrex

yea that's fine, relay coil is very low amperage