What type senders do I need, standard insulated earthed?

First of all let’s explain what standard senders and insulated senders mean.
Standard earthed senders tend to have one terminal which is where you connect the signal wire from the gauge, and the sender earths itself through the engine casing. Insulated senders tend to have two terminals, one terminal is for the signal wire from the gauge and the other is to run to an earth/negative on the battery. So the first thing to check is if your engine is standard earth insulated earth. A good way to do this is to see if the negative terminal of your starter motor is connected to the engine. If it is then it is more than likely that your engine is standard earthed and you can use standard earthed senders. If you find it is connected to the negative of the battery then you are best to use insulated earthed senders. If in doubt we recommend consulting a qualified and competent Marine Auto Electrician.