Fuel Pump, 1970 Fiat Spider

I have a 1970 fiat spider that i want to add an electric fuel pump to. On the fiat forum, they all have the pump running constantly with the key on. I don't like that since I find myself sitting in the car listening to the radio a lot while the wife is shopping. I would like to have the fuel pump run for 2 to 4 seconds when the key is turned on. I have ideas for it running while starting, but i want to figure this first part out. I looked at the constant to momentary relay diagram, but i'm still confused. for let's say a three second timed output, what size capacitor would i use? would i still only need a 10k resister?

Is there an Accessory position on the ignition switch?

When they on the forum say the pump should run anythime the key is on, I think they are meaning when the key is in the run position. IS the spider also called a 2000? If so, there should be a pink or red wire at the ignition switch that is hot in the run position as well as start.

The simplest fuel pump relay is one controlled by the alternator charge light.
Primimg can be via the starter circuit - either by using an SPDT relay or by combining alternator and starter signals thru diodes to the relay coil. EG...
(with thanks to Tezza; & "Reg" is the alternator's/regulator's D+ or L or dash "charge light" terminal/circuit)

FYI - the above method is often used for fuel cutoffs, electric chokes and - without the prime - for battery isolators, DRLs, etc.


Another option is a tachometric type relay as commonly used with Bosch EFI systems, eg VW 321906059, Porsche 433906059.
Those are often 555-timer based circuits which have power-on priming of typically ~0.8 to 2 seconds (albeit hit & miss). One catch is that their priming period is also their turn-off delay (after the last spark or injector signal) but their circuits are available.   

I'm intending a PICAXE design which would have no off delay despite (say) a 3-second prime period. (That's part of a "UIBI Mk-3" design LOL.)


IGN +12V fuel pump control is pretty stupid and often quite illegal - especially in competitions! (Even my IGN +12V plus manual switch is useless when crashed and incapacitated.)

Oil-pressure controlled pumps are better than IGN +12V though still not safe, but they are extremely stupid if used for engine protection purposes. (Oil pressure should play no part in fuel pump control. And fuel pumps should play no part in petrol engine protection.)

i am an idiot wrote:

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Is there an Accessory position on the ignition switch?

When they on the forum say the pump should run anythime the key is on, I think they are meaning when the key is in the run position. IS the spider also called a 2000? If so, there should be a pink or red wire at the ignition switch that is hot in the run position as well as start.

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That would make things easier but there are only 3 positions. Off on and crank

Italian car, accessory switch?.......

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Amateurs assume, don't test and have problems; pros test first. I am not a free install service.
Read the installation manual, do a search here or online for your vehicle wiring before posting.

Fire a latching relay from the start position, that will feed a regular relay if the pump draws more than 10 amps, use the ignition wire as the "off" or NEG side of the latching relay.


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Amateurs assume, don't test and have problems; pros test first. I am not a free install service.
Read the installation manual, do a search here or online for your vehicle wiring before posting.

If not using any of the "automated" implementations, I'd suggest an on-off switch. Preferably for the radio (who wants a burnt out ignition coil?) else for the pump.