99 379 wabco abs relays near abs computer

Discussion in 'Peterbilt Forum' started by simonsocm, Jun 21, 2021.

  1. simonsocm

    simonsocm Light Load Member

    Aug 17, 2019
    I've got a 99 379 with a wabco D series computer and I'm trying to figure out why I'm not getting power to the abs wire on my (one of two) trailer pigtails.

    I have the fuse cover like the link below but down have the second relay closest to the center, looks like it's wired for it though. My brake lights work however so I'm unsure of what it does.

    2005 Peterbilt 379 (Stock #P-2824) | Dash ###'ys | TPI

    I also don't quite know what's up with the two trailer pigtails as one seems to only have taillights and a wire that always has power on, even if the abs wire is pulled it's still got power. Looking under the dash it doesn't seem like any of the trailer wiring has been messed with under there. Under the hood the main pigtail that everything but abs works on is all connected to the factory plug. The other like I said has 4-5 not connected anywhere. I'm unsure of how it's supposed to be from the factory but regardless I'm not getting voltage to the abs pin on the pigtail.

    I checked behind the dash and I didn't have any bulbs for abs or trailer abs. Swapped one to abs and pushed in the abs diagnostic button and it showed a blink code of 7-2 which looks like it is for an ATC valve. It's a 99 though with obviously no traction control. Not sure if I'm looking at the right blink code list though.

    Previous owner was a farmer who I don't think cared that the abs wasn't working from what I'm seeing. Anyone care to give me some info? I'm planning on putting a relay in that spot when I get a chance as well as putting bulbs behind the dash. Otherwise though, is there anything else I should double check?
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