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Daniel Wilson
Daniel Wilson,
Category: Medium and Heavy Trucks
Satisfied Customers: 5403
Experience:  Owner at DJ Wilson
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Here's the deal. 2007 Peterbilt 385. Driving down the road

Customer Question

Here's the deal. 2007 Peterbilt 385. Driving down the road at night with the brights on and hit a bump in the road and the brights went off.
1. changed the blinker / light control on the steering column.
2. checked all fuses/ good.
3. found that the high beam fuse don't receive power when the bright switch is pushed.
4. hot wired power to the fused side of the brights and the brights worked.
My problem seems to be between the fused box and the steering column. Is there and relay of some kind that I'm missing?
Submitted: 1 year ago.
Category: Medium and Heavy Trucks
Expert:  Jeremy replied 1 year ago.

My name is ***** ***** I will assist you.

I believe on your model there is a relay under the glove box. You pull the glove box out to get to the relays. You should have a relay for each headlamp and one relay for the brights.

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Customer: replied 1 year ago.
Jeremy, behind the glove box is just the wiring harness, no relays or fuses.
Customer: replied 1 year ago.
Get back with me on this.
Expert:  Jeremy replied 1 year ago.

I'm thinking of a new truck.

The relay on yours will be outside the cab, driver side.

CLICK HERE for the Peterbilt Tech tip video. This should be the same for your truck

Customer: replied 1 year ago.
Will take a look but don't remember seeing anything.
Expert:  Jeremy replied 1 year ago.


Customer: replied 1 year ago.
Nope, no other relay panels outside the cab under the hood. There's only Two that was found. Under the dash on the drivers side and one in the sleeper.
Expert:  Jeremy replied 1 year ago.

I'm going to opt out since your truck is apparently set-up different than all the other 385 models on the road...

Expert:  Daniel Wilson replied 1 year ago.

Hi, My name is***** will be glad to try to help further. Click on this link for some schematics for that vintage truck and see PDF page 17 for the headlamp circuit. Schematic.

Check all the harness connections and connector pins for corrosion or loose/damaged connections. Look for chafed wiring in the harness and the firewall connections and hood. Try doing a wiggle test on the harness when the problem is present to see if you can get the lights to come on and off by pulling /wiggling and manipulating the harness. Try swapping your relays with a known good one for test purposes and check for loose connections in the fuse panel. If that all checks OK look for loose grounds and test power or continuity of the multifunction directional switch. Let me know the results and if you need more help.

Customer: replied 1 year ago.
Dan, the truck is on the road and we plan on trying to get to the problem at hand as soon as we can. I can put a hot wire on each fuse relay in the fuse box for the high beams and the work so that's telling me from the fuse box out to the headlights that all is good. What I don't have is power to the fuse relay when I flip the high beam switch on the steering wheel and I already changed that. It has to be in the dash somewhere.
Expert:  Daniel Wilson replied 1 year ago.

Thanks for the update. Click here and see PDF page 17. are two modules, one 12 and one 21pin connectors as well as a turn stalk module in the circuit. Test for power and ground at the modules and coming out as well as inspecting the wiring and connector pins for damage. The schematic will help identify the high beam circuit pins from the modules. You likely have either a harness issue or a faulty module. LEt me know