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Author Topic:   Wiring a Fuel Gauge
hauptjm posted 02-13-2013 01:27 PM ET (US)   Profile for hauptjm  
When installing an electric fuel gauge, what would be the preferable way to wire?

I have a new Evinrude gauge and would like to wire the fuel gauge such that it becomes active only when the ignition switch is on (I guess that is obvious). Sending unit is already built into the tank and ready to accept wiring.

Thanks in advance.

PS, what would be the recommended wire gauge?

jimh posted 02-13-2013 01:38 PM ET (US)     Profile for jimh  Send Email to jimh     
You probably have a fuel tank level sender that is a rheostat. A constant voltage is supplied to the gauge. The current path is through the gauge and then to rheostat. As the tank level varies, the resistance changes, changing the current flow indicated on the gauge.

The sender may have one or two terminals. If only one terminal, it is using the fuel tank as the ground. This is an old-fashioned method. The newer method uses two terminals on the sender.

If you have a two-terminal sender, you run two 16-AWG wires to the sender. One wire is for the gauge S terminal and the other is for the return to negative.

If you want the gauge to only work when the ignition key switch is in the ON position, use the ACCY circuit from the switch as the source of current for the gauge. This is usually the violet conductor.

To get more repeatable measurements, install as 12-Volt Three-terminal regulator so the feed to the gauge and sensor is always regulated to exactly 12-Volts. This will make the readings isolated from battery voltage fluctuations. As long as the battery has 12.0-Volts, the regulator will keep the voltage constant.

swist posted 02-13-2013 02:07 PM ET (US)     Profile for swist  Send Email to swist     
Hmm, Unregulated voltage. yet another reason why small boat gas gauges are notoriously inaccurate.
L H G posted 02-13-2013 03:54 PM ET (US)     Profile for L H G    
Jim - I have the fuel gauge wired that way on my classic 19. I'm not real familiar with OMC analog gauges, but I assume they have 3 posts, ignition (purple wire), neg, and sender (pink wire). For ignition key switch activation, it is wired into the instrument cluster, the same as any other gauges where the ignition and neg wires jump from gauge to gauge. Simply bring the pink and black wire from the tank sender to the correct posts on the gauge.

I think pink is the correct color code for fuel gauges, but it can be hard to find. Standard 2 cable black/red can be used, as long as it is marked and not confused with house wiring.

hauptjm posted 02-18-2013 03:22 PM ET (US)     Profile for hauptjm    
Thanks for the information. I'll update when done.

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