I came across a vehicle where the owner used the electrical connection on the fuse box to install his positive connection for his off road lights.

How safe is this?

Could this be better then attaching to the positive battery post?

Or is this more dangerous and possibly overloading the fuse box?

 

Depends on what fuse he used and if he was drawing power from the fuse box side or load side of the fuse

Fuse box will have a few Power "buses"
A Bus is just a common term for a "power bar" shared by several fuses, it would be the 12volts IN inside any fuse box

There will be a Full Time Bus, gets 12volts whenever the battery is hooked up, brake lights and head lights have full time power, as does clock in the radio and keyless entry system

Then there will be Key RUN Bus, only has power when key is ON in RUN position
And Key in ACC Bus, only has power when key is in ACC position

A fuse connects the Bus to the Load, the device getting the voltage, so a fuse terminal has a 12volt IN(the Bus) and a 12v OUT, the load
If you add a connection to the Load terminal of a fuse then that fuse would protect the added device for that fuses amp rating
If you connected it to the Bus side then you should add an inline fuse to protect the added device, but will also be using the Fuse and wire for that Bus

In say a 1996 Ranger the Ignition switch uses a 50amp fuse in engine bay fuse box which will power the Key ON and ACC buses in the cab fuse panel
Then there is another 50amp fuse in engine fuse box that powers the full time power bus in cab fuse panel

So the wire to the bus, and the bus itself, will be rated for at least 60amps, probably more like 80amps, if its being protected by a 50amp fuse, otherwise the fuse couldn't protect it, wires would melt before fuse blew if there was a short

You can pull out a fuse and then use a voltage meter to test which is the 12V IN and which is the Load, with fuse out only one terminal would have 12v, and it also tells you if its a key ON Bus or full time, either should have a 50amp fuse protecting it

If possible find the amp draw for the Driving lights, so you can see if there is a danger of overload

 

Looks like I wasn't clear enough.

Basically he attached the wiring harness to the power input cable that is tied down with the bolt at the end of the fuse box. The ground was just attached to the body frame.

The off road lights has its own relay and fuse boxes.

Thank you for the response. I appreciate it.

 

Should be fine that way, same as hooking to the battery

He is connected to a power bus and if this added wire is fused then all is well, although I would fuse it at the connection to the bus

A fuse should always be as close as practical to the 12v power source, so the wiring to the device(s) is protected

12v power-fuse----------------------------------------------switches, relays and/or devices

If you do it this way,
12v source--------------------------------------------fuse--switches, relays and/or devices

The wire between 12v source and devices is not protected so short on that wire will melt the wire and maybe start a fire

 

Thanks for the response. I appreciate it.