I plan on mounting a 12v compressor in my Sammi. The compressor has an inline fuse in the power cable & it's own on/off switch. Is there any problem with wiring it straight to power? IE Negative to negative battery terminal, positive to an ignition wire (only hot with engine going). Or do I need to use a relay and another switch.

Cheers

I wired mine directly with no problems.

Cheers Jeff

I highly recommend putting an inline fuse on the positive lead, close to where you tie into power.  I once lost a 4x4 to a redneck engineers idea of wiring without proper fusing.. burnt to the ground before the fire dept. could show up.. all because of an unfused accessory wired direct. It SHOULD have blown the circuit to which it was wired, but it did not. The wire got grounded through a tear in the insulation, to a body panel.

an inline fuse is cheap insurance, and protects whatever circuit you tie into also.

The compressor came with a 30amp inline fuse on the power lead. Are you saying if I mount it in the rear of the vehicle I should add another inline fuse close to the battery?

You need to go direct to the battery, the one fuse you have now is ok,make sure you run at least 10 guage wire for the extra amount that you need, also make sure your engine is running when you use the compressor or you will blow the fuse.(I see Q dawgs point but I use alot of wire loom wrap so everyones install is diffrent) you should see what i'm using for power managment. p.s. went and bought a new battery today, you should see the price on yellow top optimas here,209.00 I think they just got stupid.

Sorry to be a pain. Are you saying I have to connect the positive wire directly to the battery? I can't connect it to the back of the fuse box or something? I didn't really want to have power running to it ALL the time.

Yes to your battery, you can put a knife switch on the battery for like eight bucks if you have dual terminals like my battery, your stock wiring harness has a fuseable link in it that will blow if you hook it to your fuse box,(the comp with all of your other stuff turned on also) so better safe than sorry and trying to fix a fuseable link on the trail. my comp is a mv-50 2.5 cu. feet per min. so close to yours I guess.

Thanks for the info. Directly to the battery it is!

I agree, and when you do THAT, you had BETTER put a fuse RIGHT AT THE BATTERY.

I am saying the fuse for the accessory needs to be RIGHT WHERE YOU WIRE INTO THE POWER, be it the the battery or anywhere else. That way, if it EVER grounds out, or the compressor takes a crap, the fuse will blow, instead of heating the wire up to RED HOT and burning the truck to the ground.. would you like photos of my last $5000 loss???

This is 30 years of experience talking, starting at screwing things up at age 15. (I am 45)

and the $200 yellow top Optima was part of the loss... take a look


THIS was the result of a redneck mechanic, wiring an accessorie DIRECTLY TO THE YELLOW TOP, with NO FUSE!!!!

Sorry, for all the questions.
Can I run the positive wire from the fuse box if I use a relay?

You can run a small wire from the fuse box to activate the relay, but the larger load carring lugs on the relay one goes to the compressor and one would go direct to the battery and also another fuse or two(one on small wire and one just at the battery) in there somewhere.

Thanks. What size fuse would I need on the small wire from the fuse box?

I would say about five amps should be more than enough. if you run a ecm or a computer in your rig I put a diode on mine to save the switch and the ecm from voltage spikes, but thats another story,