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5 pin relay weirdness

Fang16

Apr 30, 2015
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Apr 30, 2015
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Using a 5 pin relay in a 12 volt automotive system to run the fuel pump. The pump only runs a few seconds then shuts off. The pump is wired to pin 87 on the relay. When the pump quits, pin 87 (with the pump wire removed) has no power reading with a multi-meter. Pins 85-86 and 30 still have their respective power figures of 12 volts on 30, around 6 volts on 86 and ground on 85. There is a rocker switch on the dash that controls energizer power to the switch and 12 volts to pin 30 is controlled by the ignition switch. I've tried two 5 pin relays with the same results.
 

davenn

Moderator
Sep 5, 2009
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hi there
welcome

all those numbers mean nothing to us .... show us photos of the relay and annotate it with what wires are going where
link us to a datasheet for the relay

Dave
 

Tha fios agaibh

Aug 11, 2014
2,252
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Aug 11, 2014
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2,252
Changeover_relay.png

If you have power on 85 and 86 your pump should be on. If you know the coil is energized, try jumpering terminal 30 to 87. If the pump turns on, the relay contacts are fried.
 

Kiwi

Jan 28, 2013
471
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Jan 28, 2013
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Those numbers are standard for automotive relays.

The 6 volts on terminal 86 is too low for reliable relay operation in a 12 volt system.
Is this measured with the relay connected, or with the relay removed?
What is the voltage at the rocker switch?

Is the rocker switch the only item that turns the relay on, or is it also connected to a fuel injection system?
Can you provide more information on your application?

As suggested above, linking terminals 30 and 87 with the key on should make the pump run continuously.
 

shrtrnd

Jan 15, 2010
3,876
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Jan 15, 2010
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A lot of times this happens when you have corroded electrical contacts (reduced voltage).
Are the relay plug-in contacts clean? Are any of the wires to the relay socket, or elsewhere in the circuit corroded at the contact ends?
 
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