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Boat Wiring Advice

Marine Electrical Tips, Tricks and Troubleshooting

Marine Wiring Articles on...Fuel Gauge

…or, eventually, it will run out of gas.

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Hey Kevin,

My name is Tim and I have a 1977 Caprice boat with a 175 Evinrude on the back.

I can’t shut the boat off. Evinrude-magneto

I changed the key switch and it made no difference. My gauges aren’t working properly either, any ideas?

Tim

Tim

I would check the ground (black) wire for your gauges. This is probably the same ground that connects to the ignition switch. When the ignition switch is turned off, this ground is connected to the Magneto ground (black/yellow wire).

If this ground is not connected, the engine will definitely not shut down and the gauges will not work properly.

Hope this helps,

Kevin

…or it might just be great mileage.

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Hi Kevin,

I have a 96’ Scout with an internal gas tank.

When I turn the ignition switch to on, the fuel gauge immediately pegs high (past full) and stays there.

Before I get too intrusive I was wondering if you have any suggestions?

Thanks,Fuel-gauge

Drew

Drew,

A pegged full fuel gauge usually means the sender is stuck in the “up” position or that there is a short in the pink sender wire.

Here are the steps I would take:

  1. Disconnect the pink wire from the gauge. If the gauge is still pegged, replace the gauge. If not, reconnect.
  2. Disconnect the pink wire from the sender. If the gauge is still pegged, the pink wire has a short in it between the fuel gauge and the tank. If not still pegged, the problem is the sender.
  3. Remove the sender.Determine if it is a mechanical or an electrical failure. A mechanical failure will be obvious. To test for electrical failure, connect an OHM meter where the two wires were connected. You should read 33 ohms for full and 240 ohms for empty.

One of these steps will locate your fuel gauge problem,

Kevin

Kevin

Thanks for your quick response. 

Looks like a sender problem since I eliminated the gauge based on your comments.  I removed the sender yesterday and it looked in good shape but will need to go back and check the resistance. 

Again – thanks!

Running On Empty

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Kevin,

I bought a brand new Bass Tracker Pro Crappie and, with my luck, have one problem with it. Could be worse I suppose.

The fuel gauge is not showing the correct amount of fuel. Empty or full, it reads empty. When switched on the needle actually drops below E a little, very little, slow movement.

I checked the gauge by grounding it, it seems to be fine. I checked the sender, it seems to be fine. Also, as far as I can tell, the wires seem to be fine.

Here’s the part I don’t understand. All the gauges ground to the trolling motor battery, so I used a jumper wire from the ground on the sender to the trolling motor battery. Still reads empty. So, I used the jumper to the cranking battery, the gauge worked fine. Showed correct fuel quantity.

I suppose my question is, why would everything work, while being grounded to the trolling motor battery, but the fuel gauge will not? And, should the gauges be grounded to the trolling batt or the cranking battery? Does it matter?

Thanks

Matt

Matt,

Your boat wiring problem can easily be cured.

The fuel gauge is basically an OHM meter. 247 ohms for empty and 33 for full. The gauge measures this reading by comparing its ground to the sender’s ground. If the sender is connected to a different ground (your trolling motor battery ground), the gauge will see a resistance much higher than 247 ohms which would make the gauge drop below E. When you add a ground wire from the sender to the same ground that the fuel gauge is connected to (your starting battery), the gauge works correctly.

The rest of you gauges work properly because their senders are mounted to the engine. Your gauges are connected to the engine harness that is grounded at the engine.

Carefully connect all of the grounds together on your boat. I would recommend using a good quality ground block. Connect only a single wire to each battery ground from this ground block.

Hope this helps,

Kevin

Wiring a fuel gauge

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Kevin

I need a diagram on how to wire a Tempo 3 post fuel gauge..can u help?????

Randy

Hi Randy,

This should help.

Kevin