front grill lights come on during braking

[Big Paul]

Where do I start when I apply the brake pedal and both brake lights and grill running lights come on ?

 

[crazy4offroad]

Start at the taillight housings. You might need a helper or a stick the correct length you can wedge between the brake pedal and the seat to make the lights come on. Drop the tailgate and take out both taillight housings. While the brake pedal is being held try to see if the brake light bulbs are functioning correctly, meaning the brake light filament is working in both, the park light filament is NOT lit, etc. Make sure someone didn't put just any old bulb in one of the brake light sockets. Check the ground wires. If anyone has ever fiddled with the wires behind the dash, or if the dash has been changed it may be possible the hazard light wire was used instead of the brake light wire, or the instrument cluster is for a different year range. Hope this gets you started.

 

[T-ROD]

Ive seen that issue a few times, check the bulbs on the left and right rear, they should be 1157s, some people put 1156s, or 67s in there, they are single contact, the 1157s, 2057s, or 2357s will be double contacts, and will work, but if its a single contact it will short the brake and tail light wires, so parkin lights while braking, and vice-versa, does your hazard blinkers work?

 

[chengny]

Here is the wiring diagram for the rear lighting system (and lamp no.s):

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The yellow wire is hot when the brakes are applied and if a short exists over to the brown wire (anywhere in the circuit) the truck will light up like a Christmas tree when you step on the brakes.

I bet, if you feel like checking, that in addition to the front parking lights - the license plate lamps and all four corner markers also illuminate when braking (and cab roof lights if you have them). It must look awesome to other drivers.

Note the single pole lamp for stepside applications.