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Relay wiring


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I plan on installing an electric fuel pump on my 35 Buick with an original straight right 6 volt system and was wondering how and where to install a relay for it,pictures will be appreciated,Thanks,Greg.

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It's really straightforward. I assume you'll be using a Bosch-type automotive relay. Some are SPDT with five terminals and some are SPST with four terminals. Either one works for this application. Even the cheap ones at chain stores are 30 amp or higher. The only thing you need to know is that the 30 and 87 terminals are the ones that are switched on and off by the relay. The 85 and 86 terminals are the coil that you control with your dash mounted switch.

 

Fuel%20Pump%20Relay.gif

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I like to use NOS 6V Delco headlight relays for my fuel pump installations. I wire them so they're pulling power directly from the battery or starter (or kill switch, if that's where the positive battery terminal is located). Don't use the ignition switch for power, just as the "trigger" for the relay, and if you use a toggle in there, then the fuel pump will only run if both the ignition AND the toggle are on. If either one is off, the pump won't run. The vintage relays blend in better than a modern Bosch unit. They all have their own configurations, but here's a typical wiring diagram:

 

FuelPumpWiringDiagram.thumb.jpg.f6933101d3c13ad7c59f959546fbc26b.jpg

 

Here's how the Delco relays look in a vintage engine bay:

218Relay1.thumb.jpg.b03370e6614908809e090473a3fcef13.jpg

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Yes, the fuse is built into the relay. I buy them on eBay when they're under $30. Sometimes they come in these neat little boxes and I feel badly tearing them open. Use a headlight relay instead of a horn relay, which may or may not be rated for constant duty. If you look for 6V relay on eBay, you'll find a bunch. There are a variety of different types, they should all work about the same although the wiring is sometimes different. This is the type I prefer simply for the built-in fuse.

 

Relay1.thumb.jpg.108fe0745a4d5d1b1765a7d6dba88ee0.jpg

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On 3/3/2021 at 3:09 PM, joe_padavano said:

It's really straightforward. I assume you'll be using a Bosch-type automotive relay. Some are SPDT with five terminals and some are SPST with four terminals. Either one works for this application. Even the cheap ones at chain stores are 30 amp or higher. The only thing you need to know is that the 30 and 87 terminals are the ones that are switched on and off by the relay. The 85 and 86 terminals are the coil that you control with your dash mounted switch.

 

Fuel%20Pump%20Relay.gif

Will a 12 volt relay work in a 6 volt system?

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