[J-Dub]

I have recently bought a 2007 Reno and discovered that the brake lights come on when I switch on the head lights. Does anyone know what would cause this?
Brake lights work normal when the headlights are off so i don't believe it's the brake switch attached to the pedal.

 

[fordem]

This may sound like a silly question - but how do you know it's the brake lights that are coming on and not the tail lights? Many cars use a single brake & tail lamp bulb, and the tail lights come on with the first click of the light switch, before the headlights which are on the second click.

Check for a defective ground in the light wiring.

 

[J-Dub]

I know this because the middle brake light on this comes on when I turn on the headlights

 

[fordem]

Gotcha - center brake light comes on with the headlights.

Now - I'm not certain how the headlights on a Reno are wired - I believe that's a Daewoo built vehicle not a true Suzuki - so the wiring may differ from Suzuki's norm which is negative switched.

Anyway - if you have positive switched headlights and a defective lighting system grounds - it is theoretically possible to have current flowing through the headlight filament, and instead of going to ground, going through various park light & tail filaments into the brake light circuit - if this is the case you should see other strange combinations of light brightness as lights or switched on and off.

What I would do is take a look at the wiring in the vicinity of the headlights and tail lights - look for wires going to bolts on the frame - remove the bolt, clean up the terminal that's underneath it and reconnect. Also remove and check the actual headlight & tail light connectors for corrosion and clean and/or replace as required.

 

[J-Dub]

I've already inspected the wiring in the tail lights. I didn't see anything unusual. I've heard this could happen if there's a double filament bulb that is defective. So I took out those bulbs and the brake lights still were on. I will take a look at the grounds as well as the headlight fixtures. Thanks

 

[fordem]

Unplug the headlamp bulbs and the stop & tail bulbs - if the center brake light still comes on when the headlights are switched on, there's a short in the wiring somewhere.

 

[J-Dub]

I found the issue. The previous owner had put the wrong bulbs in the tail lights. They had a single prong bulb in two of the sockets that were two prong sockets

 

[fordem]

There you go - he most likely created a short circuit - still that should have brought the brake lights on with the park lights, not the head lights.

Another thing that puzzles me - how did he get the bulbs in there? One style of bulb has the bayonet pins directly opposite one another, and the other has one of the pins offset, and the reason they are that way is to prevent that very situation.