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Old 11-12-2014, 05:16 PM   #1
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Onboard air wiring/fuse

I recently got an air compressor and tank which I'm fabbing up a rack for now. It's going to be right in front of the rear bumper between the frame spars, behind my water tank. I'm looking for the easiest way to wire it and I have an 8 guage (I think) wire right there in the trailer brake wiring, which I'm pretty sure is already keyed power and fused at about 40 amp under the hood. Anyone see a problem with wiring my compressor off that available circuit? If I ever do tow a trailer with brakes, I don't see using the compressor any time the brakes are applied. The compressor will be switched anyway. The compressor has an 8 guage lead and recommends 8 guage for a long wire run (20').

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Old 11-16-2014, 11:54 AM   #2
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Re: Onboard air wiring/fuse

Anyone?
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Old 11-16-2014, 12:31 PM   #3
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Re: Onboard air wiring/fuse

Trailer brake circuit is not keyed. It is always on. The "up-fitter aux power" circuit is keyed but only fused for 30 amps. This will be in the harness which looks awfully similar to the trailer brake connector.
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Old 11-16-2014, 01:18 PM   #4
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Re: Onboard air wiring/fuse

I recommend running a dedicated fused line. Piggy backing electrical components is never a good long term solution.
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Old 11-16-2014, 05:15 PM   #5
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Re: Onboard air wiring/fuse

Thanks to you both. CarringB, it sounds like this is what I need to use. Are you saying it's in the same spool as the trailer wiring, just not used? If so, do you possible have a schematic that would tell me what color the wire is? 30 amp is all I need, that's what the air compressor is fused at anyway.

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Old 11-17-2014, 06:18 AM   #6
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Re: Onboard air wiring/fuse

Scotty here's how I'd approach this..........

Run at minimum 8 gauge wire from the underhood junction box through a suitable relay whose output would feed the compressor. Out of this relay run the wire to the compressor mounting area, securing and protecting it from chafing, vibrations all along its path. Honestly I'd use 4 gauge but 8 is fine for that load & distance.

Connect that wire to the compressor, securely ground it to a close place on the body/frame and you should be good to go.

If your compressor has a pressure switch I'd power the relay only with key on in the start/run ignition switch positions to prevent the compressor draining the battery.

As suggested using the existing wire for this application isn't the best way.
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Old 11-17-2014, 09:01 AM   #7
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Re: Onboard air wiring/fuse

Thanks JWA. I'm going to post the wiring diagram for mine here soon. I'm in no huge hurry with this project, especially given the arctic weather lately. I think the relay is overkill since it already has a switch at the gauge. The wiring diagram should explain. Anyway, I'm still real curious about any up fitter wiring already in place. I do see that the trailer brake circuit might not be wise. I don't mind running a wire the length of the van but hate to if it's truly not needed.

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Old 11-17-2014, 09:04 AM   #8
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Re: Onboard air wiring/fuse

Quote:
Originally Posted by JWA
...If your compressor has a pressure switch I'd power the relay only with key on in the start/run ignition switch positions to prevent the compressor draining the battery.
and waking you up at random times during the night
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Old 11-17-2014, 09:27 AM   #9
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Re: Onboard air wiring/fuse

The up fitter power plug is not the same as the trailer brake controller plug, but it looks nearly identical on the '94 vans, while its round on the newer vans. I'm not sure which year they switched the connector shape. Either way, it should be attached to one of the wire looms near the steering column. It is not the same as the trailer brake connector, but might be the same shape on your van (and in the same general area). This circuit is fused and runs through a relay in the power distribution box, so it can save some wiring hassle. You'll need a test light to probe the connector to find which one is keyed (one is constant, the other 2 wires are just "pass-though" circuits from under the hood).
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Old 11-17-2014, 10:28 AM   #10
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Re: Onboard air wiring/fuse

I'd go #6 str copper and a 50 amp breaker mounted by the starting battery with a 100A relay in the mix. That should cover most compressors if you need to upgrade down the road. Best to do it once and not have to redo something at a later date.
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