Electrical problem

Good eye, Tim.  I missed the exhaust pipe and didn't realize where we were in the airplane.  It's obvious now that it's a Rotax starter contactor.  So, the other heavy white wire coming off the left (battery side) terminal of the contactor must go to a battery contactor somewhere else.

I'm still confused about how this is happening.  With the engine off and the Battery Master switch off, there should be no power on the OVP yellow wire.  If that's true, then there's no way the red wire could power the starter.  Somehow battery power is getting to the OVP with the engine and Battery Master turned off.  But, if the OVP yellow and red wires are both connected to the battery then the device can't do anything to protect the battery.

Thinking about the OVP's internals, it must power its relay coil via the red wire, switching the low side of the coil to ground via the blue wire.  The connection from yellow to red must be normally closed, and opened by activating the relay when battery voltage is too high.  So, it's either a SPDT or SPST-NC relay, and there's a current path from yellow to red when the device is at rest (coil deactivated).  If all of that is correct, then there's no malfunction in the OVP.

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Gregor, I agree with Tim.  It looks like the OVP red wire was connected to the wrong side of the starter contactor.  Unfortunately, there isn't enough stud length on the other terminal to add it, so perhaps you can connect it directly to the battery.

I don't see a fuse in the OVP red wire.  The black inline fuse holder shown in Picture 2 has a blue fuse (15A), not clear (25A).  Is this the fuse that is blowing?

If so, where are the red wires from each end of the blue fuse connected?  Is the OVP yellow wire connected to one end of the blue fuse?

Is this a new problem that just started happening on an existing installation, or was the OVP recently installed?

The black inline fuse holder are mounted on the red wire for the OVP, its correct that the fuse are blue 15A but its was only for testing because i ran out of 25A fuses, and yes that is the fuse that is blowing.

The problem is new that just started on an existing installation, the OVP was already installed when the plane was bought 3 years ago.

So if i understand right, i should try to move the red wire to the other side of the starter relay or direct to the battery ?

Thanks in advance 😀

There must be something that I can't see in your Picture 2.  Please look at the image below.  I have highlighted the OVP red wire with a green line.  It goes from the OVP directly to the disconnected ring terminal.  I don't see a fuse in that wire.

I highlighted the fuse holder wires with a blue line, and the ends are labeled A and B.  Can you tell me what A and B are connected to?

Finally, I highlighted the OVP yellow wire with a yellow line, and the end at the top of the photo is labeled C.  Can you tell me what C is connected to?

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Yes, I think you need to connect the OVP red wire to the other side of the contactor or to the battery.  It looks like you don't have enough threads on the contactor stud, so the battery is probably your best option.

If the system was working properly before this started happening, then something else has changed.  I don't know how it could have been working properly with the OVP red wire connected where it was, but again, there must be something that I'm not seeing.

Thanks Eric for your help, I appreciate that.

I will come back with answers and better photos of the wiring, next time when I go to the airfield again, hopefully sunday