Fitting a Negative Earth pump to a Positive Earth Classic car

positive earth car wiring for a negative earth pump

Things you need:

Basic multi meter

Fused relay

Pipe cutter

25amp twin core (black and red)

Fuel filter

Fuel line to suit 6mm/8mm

Facet pump (or any 2 wire pump)

6 Jubilee clips size m00 (11-16mm)

Wire cutters/strippers

Shrink tube

Suitable connectors, spade male and female

Basic tools


1939 Rover 14 new fuel pump wired for positive earth

Firstly disconnect and remove the battery

Now decide where you would like to mount the pump. It needs to be as close as possible to the tank. Most pumps are made to push fuel not suck.
If possible its best to mount the pump directly to the chassis using rubber mountings.  You will need to cut a section of fuel line out to be able to fit the pump, three pieces of fuel tube and a inline filter (always fit a fuel filter) and make sure its before the pump.

Fitting as follows

A tube form tank line to inline filter, tube from filter to the pump, tube from the pump to the fuel feed line to the carburetor, you will need 6 size m00 (11-16mm) jubilee clips.

Next investigate the wiring don't assume that all cars are the same and certainly do not think it is original!
You will need to locate a constant Negative, a switched Negative and a suitable positive from the body or chassis.
Now fit the pump making sure the flow is towards the carburetor there's normally an arrow on the pump.
Next identify the positive and negative on the pump (Red is positive Black is negative)
You can connect the positive to the body or chassis using one of the pump housing fixings (remember this is a positive earth car) Or I normally run twin core wire to the pump this is because pumps are generally located in a area where they are exposed to the elements. If the mounting bolt rusts or oxides then you will have a poor connection. 
Route the twin core from your chosen location to the pump, Join Black to Black and Red to Red using spade connectors. Use a spade female on the Negative feed (black wire) then use a male spade on the Positive feed (Red wire) use the opposite on the pump so that its impossible to connect wrongly if disconnected at a later date. slide suitable shrink tube over the connectors, shrink using a heat gun locally.

                              DO NOT USE A FLAME THIS IS NEAR A FUEL LINE

Connect the Black feed wire to pin number 87 on the relay using a female spade connector.

Connect the Red feed wire to body or chassis using a ring connector. (remember this is a positive earth car) or
use twin core as I have. One wire to Positive on the pump (Red wire) the other wire (black wire) with a female spade to pin 85 on the relay, both wires need to go to the ring connector on the body or chassis.

Next you need to run twin core from the fuse box or control box where you found a constant negative and a switched negative (off the key).

For this 1939 Rover 14 P2 it was A2 for the constant negative and A3 for the switched.

Join the Black wire to the constant negative (A2 for me) then connect the other end to pin 30 on the relay using a female spade connector.

Now join the Red wire to the switched negative (A3 for me) then other end to pin 86 on the relay using a female spade connector. Make sure you can access the relay at a later date. Tidy and secure your wiring.

Now you can prime the pump and fuel line, this is done best with a vacuum pump, sythen pump, do this at the fuel feed on the carburetor by disconnecting the line.

Reinstall the battery and reconnect.

You can now test you pump is working. It should run after turning the key it will run constantly it maybe loud at first but quieten down once pressurized.

Now start the car as normal and check for any leaks

fuel pump loction and fitting
positive earth car wiring for a negative earth pump
positive earth car wiring for a negative earth pump relay
positive earth car wiring for a negative earth pump fused relay
positive earth relay
Facet pump for positive earth
relay positive earth