That is way too much light for a stock alternator. If you have 5 150 watt lights, the current draw is 62.5 amps. You definately need a relay with atleast 85 amp or greater continuous operation rated contacts keyed from a switch. The main feed wire to such an installation should be #6 to prevent over heating and starting a fire and the leads for each light should be atleast #14 to prevent large voltage drops to the lights. Fusing is definately in order for to prevent a short or overheating the wires from starting a fire. In this case I'd run two relays so the feed wire size and fuse can be reduced. You could split the lights between them 2 and 3, or 25 amps on one and 37.5 amps on the other. That would allow you to reduce the feed wire size to #10 and #8 respectively with fuses of 30 and 40 amps to make a safe installation.
A alternator upgrade to atleast a 130 amp 3G. will be needed inorder to operate the lights and truck at the same time. You might even consider a 200 Amp alternator. Be aware that at idle no alternator may be able to supply your entire trucks requirement with those lights on, which means that you will start draining from the battery.
the relay should have numbers by the contacts;
30 = is the fused supply from the battery to the lights
87 = is the normally open contact (used to turn something on when the relay is operted)
87a = is the normally closed contact ( used to turn something off when the relay is operated)
86 = is the contact for switched 12V to the relay coil
85 = is the contact for grounding the relay coil
Personally I'd recommend reducing the lamp size to atlest 100 Watts and I'm sure you are aware that it is illegal to run them on the road.
Good luck on whatever you do with it.

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