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Ask Hank F. Your Own Question
Hank F.
Hank F., RV tech - emphasis on gensets
Category: RV
Satisfied Customers: 14406
Experience:  RV tech since the beginning of the millenium.
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Wiring Onan 7.5 DKD spec D diesel generator..connectors

Customer Question

Hey Guys,
I need a wiring diagram for an Onan 7.5 DKD spec D diesel generator on-off switch. The switch is a 0308-0827 with five connectors on the back. Can you help?
Submitted: 4 years ago.
Category: RV
Expert:  KKassel replied 4 years ago.


The wire diagrams are in the back of it

what color wires do you have?

Customer: replied 4 years ago.
I have this manual and it doesn't tell me which color wire goes where. My switch is a 0308-0827 Onan with five connections and I have five wires. The colors are: brown, red, blue, green & white. The switch has a run light in it, FYI.
Expert:  KKassel replied 4 years ago.


I will get this to HANK, he knows them all

Customer: replied 4 years ago.

Good Luck.........I have a guy going to look at a unit like mine for sale to pull the switch out and report back to me. That's where I am..............

Thanks, David

Expert:  Hank F. replied 4 years ago.

Thank you for choosing Just Answer for the solution to your problem.
My name is XXXXX XXXXX I am going to assist you with this.


What is the full model number of your genset?


On the switch, is yours configured with 3 terminals on one side, and 2 on the other?

Do you have either an hour meter or battery monitor on the remote?


Customer: replied 4 years ago.

Hey Hank,

The model of the Onan is 7.9 DKD FJ 2799 spec D Serial # XXXXX

My switch is an Onan 0308-0827 with a lighted run indicator, I have 5 connectors on the back of the switch and 5 wires. Looking at the back of the switch, yes, three connectors on one side and two on the other..The colors are brown, red, blue, green and white. The config. is 2 connectors on each end and one in the middle. The Hobbs Meter is on the control box next to the generator. I have a pre-heat switch to the right of the start/stop switch as in the photo here.

The switch should have the run light on while running; that isn't happening. It lights up as it cranks but doesn't stay on while running. And, by the way, it only runs for 15-30 seconds before sputtering out. I think it's the switch but won't know until I get it wired correctly.

Thanks for your efforts Hank........

Expert:  Hank F. replied 4 years ago.

Sorry - I was at work when you responded.


Even though there is supposed to be a standard color scheme for these wires, I have found it to not be reliable.

Not all coach manufacturers go by it - and there is no telling if wires have been changed over time.


We need to start from scratch.

This is very difficult to explain, so I will do the best I can - please be patient with me.


On the back of the switch, the 3 terminals down the one side are the actual start and stop terminals.

The 2 terminals on the other side are for the light.


What you need to do to ensure you get the correct wires, is to remove the control panel and access the engine control board.


On the board, you will see a row of connectors down each side.

All of the connectors are labeled on the board.

On one row, it starts out with STOP - START- GROUND - B+.

This is the side you need to find the wires on.


Lets begin with STOP, START, and B+.

Find which color of wire goes to B+ (let's assume it is red).

At the switch end of the harness, find that color wire. I would suggest doing a continuity test on the wire to ensure that the colors do not change somewhere in between.

That wire will go to the center of the 3 terminals - it is the common.


Now find the wire at the control board that goes to START (let's assume it is green).

Find that wire at the switch end of the harness.

Now the tricky part - the start terminal is the terminal OPPOSITE the end of the switch you push to start.

For example, if your remote switch is mounted vertically, and you push the top of the switch to start, the bottom terminal will be the start terminal.

If your remote switch is mounted horizontally, and you push the right side of the switch - the left terminal will be the start terminal.


Now go back to the board and find the wire connected to the stop terminal of the board.

That wire will go to the remaining of the 3 terminals.


Now go back to the control board.

On the other side of the board, find the connector marked SW B+.

This wire will go to one of the other 2 terminals on the other side of the switch - for the light.

It does not matter which wire goes to which terminal.


Customer: replied 4 years ago.

Hey Hank,

Thanks for the wiring info. The problem with this fix is the control box for the generator is behind the unit. The generator slides out front on tracks but the control box is still under the coach. I'll check to see if I can move it forward where the wires are accessable to identify the terminals you specified. It's really tight. I used a mirror and flashlight just to see the back of the switch on the control box earlier only to find out it was different than the one inside the coach. No color match on the wire because it wasn't part of the harness. I'm going over to look at the coach this morning and see if there's any wiggle room with the control box. I'll get back with you.

Expert:  Hank F. replied 4 years ago.



Sorry the wiring is such a mess - but that is the norm.

That's why I specified that you should test each wire - as the manufacturers rarely follow the color schemes.


Customer: replied 4 years ago.

Hey Hank,


I'll get with you as soon as I get back off the road; just a few more days....Until I get the new switch diagram problem taken care of, I just unplugged the harness at the Onan control box that goes to the dash switch and started the generator with the switch on the side of the control box. It starts fine but will not keep running without holding the accelerator lever forward and direct wiring the fuel pump to a 12 volt source. So, I might have a relay issue as well. When it's running it is producing full 110 volt AC and will run both AC units with ease. If you try to give power to the terminal on what I think is a solenoid that is shared power for the fuel pump, it engages the starter again. Not a good thing while the unit is already running. Back with you soon. Thanks, David

Expert:  Hank F. replied 4 years ago.
Customer: replied 4 years ago.

Hey Hank,

I found out yesterday that the accelerator lever I was referring to is a fuel actuator. I love learning something new everyday..........Back with you soon......

Expert:  Hank F. replied 4 years ago.



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