Does anyone have an idea on how the 3 point relay for the fuel pump works? I had assumed that the two prong end was the low current activation. On the 3 connector end I was thinking that the large gauge blue/white wire would carry the 12V and activating the relay would switch that voltage to the wire that goes to the fuel pump.

Turns out there is only voltage on that large gauge blue/white while only when starting. Once running the wire to the pump has 12V.

I ask because my fuel pump will randomly stop working and it seems to have something to do with this relay.

Thanks.

 

Here's a bit more information I've sussed out :

The crazy thing is, if you unhook the 1+2 connector that energizes the relay, the fuel pump still kicks in when you turn the key to accessories. I'm beginning to think that this is not the relay I'm looking for which begs the question, what DOES it do?

Relay in Question

Basic function

 

This diagram may help
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Home >> Mazda >> 1984 >> B Series Truck L4-2000 1970cc >> Repair and Diagnosis >> Diagrams >> Electrical Diagrams >> Fuel Pump >> Exc. Calif.

Exc. Calif.

Fig. 74 Emission Control, Ignition & Kickdown System, Fuel Pump & Slow Fuel Cut Valve. Exc. Calif.:

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Manual available here .
https://charm.li/Mazda/1984/B%20Seri...2000%201970cc/

 

That's helpful. Thanks!

I have a couple of questions though:

- Does this diagram show that the 3 point relay is Normally Closed?
- What is going on with the relay in the crank position and why is the wire from the ignition switch (LW) such a heavy gauge?

 

Don't know the answer to that question but you should be able to work it out from the diagram (if it's the correct one). Power up the field wiring of the relay and see what switching takes place. It's been a very very long time since I last worked on one of them. The heavy gauge wiring is obviously the main power feed to the pump but the size is like many things dome back then an overkill. Crank and run both supply power to the pump.

 

Relay is normally closed. It is only triggered in key position III (IG) and when cranking.

I fail to see what the point of this relay is. The fuel pump receives 12V no matter if the relay is energized or not.

Why should I not just connect [BL] to [BW] which should activate the pump in IG, ST and RUN positions?

 

I think that for safety reasons - like in a roll-over or an accident - that when the engine stops, the electric fuel pump no longer gets power.