After repairing the oil pan of our Barefoot Excel nautique 351w I got the engine back in and running.

When I faked a lake, the oil pressure was at 10psi, which i already think was weird, because last year it was around 50-60. 

but maybe when it was already hot, so I didn't think of much.

When we went to the harbor and put the boat in. The gauge showed no pressure at all. but no knocking sounds or anything as well. 

We carefully cruised at 3k-3.5k rpm and everything was fine. 

Since all the connections had been loose, I figured a loose cable or ground. 

I have personally filled and checked the oil level.

And normally we also have a red light that comes up in idle and goes away when the engine goes above 1200 rpm or so?

It litterally states ''if light is still on beyond 1200 rpm, shut down engine''. Or something similar in other words. 

But this light also does not work. 

I did had to repair and solder a wire to the oil pressure switch on the v-drive. It's not a very good one if I have to be honest. Is this the red dashboard light issue?

When I went back yesterday, the gauge was working again and showing 10psi. 

When i revved it a little, it would not increase or decrease. 

I disconnected the cable that comes from the sender and then the gauge drops to 0, obviously. 

I checked the connection at the sender, and it looks fine. I did notice a oil pressure switch on a T at the oil pressure sender, but we do not use this anymore.

The engine was a protec engine once and it is now carbureted. 

My question

1. Can I try to take out the sender without to much of a oil spil... 

2. how can i further diagnose the gauge?

3. Does this red warning light have anything to do with this or is this a problem on its own?

Thanks in advance

Gino

Belgium

1. You might get a little residual dripping, nothing else when removing the sender.

2. SInce the gauge does move, the sender is most likely the problem. Bad senders often act like yours does

     Here in the US that would be a 240 to 33 ohm sending unit

     33 ohms corresponds to 80 psi on the gauge and 240 ohms corresponds to zero pressure.

     There are European gages that don't use the same convention, but I'll guess that your boat was built with the American standard.

      If you take the wire off of the sending unit and touch it to ground with the ignition key in the RUN position, the gauge should peg high. Then unground the wire and the gauge will should go to zero. That'll tell you that the gauge responds

3.   Like you said, the Red light is for your Walter V drive. Nothing else feeds that light, Normally at 5 psi or less the pressure switch on        the v drive is closed and the  Red light will be ON. Then as RPM's come up in gear, the light will go out a little above 5 psi at about 1200 rpm. If you rev the  engine in Neutral, the V drive isn't turning so the light will stay on. No automatic actions happen. 

The light staying on means either the internal pump isn't functioning right or the switch is dead

Here's a picture of the light and the warning

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