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Electric fuel pump wiring

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Old 11-17-2018, 08:37 AM
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Default Electric fuel pump wiring

I searched all over online but can’t seem to find any info on fuel pump relay mounting. My pumps are low pressure Carter’s for carbs, only supporting 400hp each.

I understand the oil pressure switch, momentary bypass for priming the bowls, etc. but I can’t find any examples of where the relay is being installed?

Surely there is a spot on the engine on a newer efi Merc, but old school carb/distributor only type deals where is everyone mounting fuel pump relays? All the way up in the dash? Is no one using a relay? As I found it, mine is direct from ignition switch key on power... sketchy
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Old 11-17-2018, 08:55 AM
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As I found it, mine is direct from ignition switch key on power
This is all you need. If the pump draws to much current it blows the 20 amp fuse going to the key switch.

If you want to install a relay, then it would be located on the motor and the relay coil is powered by the key switch. Would need to add a fuse feeding the pump
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Old 11-17-2018, 09:02 AM
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I know it works, I guess I’m just surprised - seems a bit to shade tree mechanic but I’m so ingrained with safety from work (refinery equipment) that could a contributing factor!
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Old 11-27-2018, 03:59 PM
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I need to wire mine as well. Looks like holley pumps only draw about 4 amps so direct from ignition switch means one less relay to fail. As long as the switch is fused and the wire from the switch is large enough gauge, it should be good? Thoughts?
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Old 11-27-2018, 04:32 PM
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I personally setup a painless fuse/relay block in my bilge that has 4 relay circuits and 3 continuous power circuits off of the fuse block. I tapped into the Merc purple wire to turn on the relayed circuits for ignition, pumps, etc and it cuts everything when the tether is pulled. The continuous circuits supply the stereo memory, bilge pumps etc. I found most of the stock wires to be rather undersized for any upgrades.
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Old 12-05-2018, 09:16 PM
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I decided to go with the dual relay I found at Concours Specialties ? Custom Switch Panels and Electrical Systems

No affiliation. I’ll let you know how it comes out. What sold me:

1. Waterproof housing
2. Integrated fuses
3. Pre-Wired
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Old 12-06-2018, 09:47 AM
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I would not mount any relays on the engine unless they are specifically designed to be there. Too much vibration. My fuel pump relay sits on a small panel mounted to the transom close to the engine. There are water resistant relays available..
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Old 12-06-2018, 12:12 PM
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Originally Posted by ttrm007 View Post
I decided to go with the dual relay I found at Concours Specialties ? Custom Switch Panels and Electrical Systems

No affiliation. Ill let you know how it comes out. What sold me:

1. Waterproof housing
2. Integrated fuses
3. Pre-Wired
Those are nice systems. They have heavy enough wire that some apps need and plenty of wire for the bilge.
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Old 12-06-2018, 02:41 PM
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Originally Posted by Wobble View Post
I would not mount any relays on the engine unless they are specifically designed to be there. Too much vibration. My fuel pump relay sits on a small panel mounted to the transom close to the engine. There are water resistant relays available..
I was thinking of mounting them next to the fuel pumps likely on the front wall of the bilge in front of the engines. Shouldn't really be much vibration or water for that matter.
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Old 12-06-2018, 03:25 PM
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Originally Posted by ttrm007 View Post
I was thinking of mounting them next to the fuel pumps likely on the front wall of the bilge in front of the engines. Shouldn't really be much vibration or water for that matter.
should be fine, I would put it high enough that it's not the first thing to go under if you forget to put the bilge plug in
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