I have an RV with an Onan 4000 Genset. I have no power to the generator switch. I found that my hot wire from my battery had fallen onto my tailpipe and possibly caused damage to the generator.

limited information generic answer --you need wiring for the rv part not the p30 chassis --notify a rv dealer--rv shop --or online rv forums many of them have help and service manuals for rvs

Question edited for clarity and spelling 'Oman (the country) to Onan.
Question moved to RVs, guessing this is an RV Generator?

Troubleshooting

https://www.google.com/search?q=onan+5500+generator+troubleshooting

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If you have a meter, black lead to ground and red lead on white wire, flip the switch to start. If no voltage, solenoid is bad. A Cummins dealer can get the solenoid. Take a picture of the data plate for the serial number and model to provide them, it will be need.

If you have low voltage, the solenoid will only click repeatedly, charge your battery and try later.
If you have voltage (? 12.2VDC), then look at the back of the starter switch, you need to take a heavy piece of wire (8g or bigger) and jump the bottom big post of the solenoid to the top big one. If it has voltage and the generator does not turn over, the problem is IN the generator. Most common issue is the brushes are stuck and not making good contact with the slip ring.

the oil level sensor is a vital piece of equipment to save your engine when the oil level is too low
talk with generator repair shops as the sensor is generic and you may be able to get a good unit that fits another brand
you can test by bypassing it
however check the fuel flow through the metal tap as the corrode internally and block the flow of fuel--especially if you use e-mix fuel
the oil switch is screwed into the sump near the dipstick with 2 wires running back to a small box about the size of a match box

The code red to a low voltage or no voltage. First, disconnect your battery and check the voltage with a volt meter. If you have multiple batteries, check them individually. If you are getting anything less than 12VDC, your system probably will not even about to start; you may just get a couple clicks. If you have multiple batteries and one is strong, say anything over 13VDC, connect just the one and try starting. If the battery/batteries are strong and so nothing, ohm out the power cable(s) going from the battery to the generator "+" terminal; the cake should connect through a bridge before going to the battery or a disconnect switch. Ohm each cable individually when not connected s to anything. The readings on a digital multimeter should be around .02 ohms, which would be the same results if you touch the two loads of the meter together. The battery and cables can be easily replaced. If all these readings are good, the next thing to look at would be the transfer switch. That would be something more difficult to troubleshoot and you may want to consider taking your motorhome to a "reliable" camper shop or look to see if there are any Mobile RV certified technicians around.

You didn't indicate, but I will assume when plugged into park power your 110V AC devices (Outlets/TVs/Microwave) work?

If so that isolates it to the genset or something up to your AC/Breaker distribution panel.

Things to check in the main power from the generator to electrical main AC distribution/breaker panel:.
Some type of Breaker off at the Genset (Blown fuse?)
Some type of toggle switch/transfer switch on the wrong position
If you have a auto transfer switch it might be stuck or defective
Loose connection or a connector coming loose
Defective wiring

White Brown green and yellow are normally The 12 volt vehicle lighting colors, not 110 volt power. Generators do not have FIVE wires for the power wires out of your generator. Is this the remote control circuit? If so, I dont have a clue!

Do you have your switch turned on for your auxillary battery? That is the power source to start your generator. It also charges your auxillary battery. Hope this helps you.

Check if you have a transfer switch that is set to 'generator'