Troubleshooting Blown Fuses in Truck When Headlights Are Turned On  

Question:

Expert Reply:

Your issue with fuses blowing in your truck when you turn on your headlights could be due to any of several issues.

One possibility is that the trailer's lights present a total power demand that is more than the truck circuit is rated to deliver. If you recently added more lights to the trailer or changed to new ones this could cause this issue. You can also disconnect the trailer, replace the blown fuses and see if the problem occurs again. If not, then this tells you the problem is probably on the trailer.

Another possibility is that the grounds in your truck and/or trailer wiring may not be making a good enough connection to support the higher power drawn by the running light circuit. Since headlights/running lights remain on continuously they draw more power than turn or brake lights that are on only briefly. Check the main grounds on both the vehicle and trailer wiring harnesses to see if either is loose, or connected to a spot that is rusty or dirty. You can sand off the grounding point or move the ground ring terminal to a new clean bare metal spot. The ground needs to be made to a clean bare metal spot on both the vehicle and trailer frames.

You may also have trapped foreign material like a strand of wire, dirt or water inside the connectors that is causing a short when you turn on the headlights. Check both vehicle and trailer connectors for any signs of foreign material or corrosion that could be causing a short.

There are spray-on electrical contact cleaner products, such as Caig De-Oxit, which may do the trick but if the connectors are in bad shape we can help you with replacements, such as vehicle socket # HM48470 and trailer plug/junction box # HS381-9000.

expert reply by: Adam R

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