Brake Lights - Puzzled?

[Duffman]

Ok, brake lights used to work fine on my 70 240Z, then worked periodically and now don't work at all. Checked the brake switch, it works fine (used voltmeter to confirm power). Hazard lights work fine, with the brake lights going on and off with the other lights. So, brake switch and hazard switch work fine, does that mean my problem lies in the T/S switch? Based on what I pulled up in the archives, am thinking that is the case. Thoughts?

Edited October 25, 2012 by duffman

[Wade Nelson]

I'm not convinced the hazard switch powers the brake lights. It may be illuminating the parking lamps.

Start by checking or replacing one of the brake light bulbs. Simple and cheapest, FASTEST fix there is.

If that does nothing for you, grab an assistant, and determine if you're getting POWER to the brake light socket. If so, then you're missing your GROUND connection --- usually a wire screwed to the body somewhere back there, often rusts off or gets loose. Needs a star washer.

If you've got GROUND (continuity) at the socket, but not power, and you have power at the brake light switch, try running a jumper from the brake light switch all the way back to the brake light. If it works, you've determined your problem --- a broken wire somewhere BETWEEN the brake light switch and the rear of the car.

GL.

[beermanpete]

Yes, check the turn-signal switch. The hazard switch feeds the brake/turn signal lights in parallel with the turn signal switch.

[Duffman]

Ok, checked the T/S switch, no issues there. Also, took apart the hazard switch and gave the contacts a good cleaning, now that works better. However, I am still finding my brake lights work with the T/S switch and the hazard switch but not as brake lights by themselves. If I had a broken wire or ground issue somewhere from the switches to the tail lights, wouldn't I be having problems with the brake lights working with the T/S and hazard switches?

[beermanpete]

The power for the brake lights flows from a 20A fuse in the fuse box to the hazard switch, then to the stop light switch, then to the turn signal switch, then to the bulbs at the rear of the car. The brake light contacts in the hazard switch are not used for the hazard function so they could be bad and the hazards will still work. The contact in the brake light switch is used only for the brake lights. The contacts in the turn signal switch are not used for the turn signal function so it could be bad and the turn signal will still work.

A connection could seem ok with no load but fail when a load is applied (the brake lights) due to high resistance from dirt, corrosion, wear, etc. In some cases a voltmeter does not draw enough power to identify a marginal connection. You need to monitor the voltage with the load applied (step on the brakes) and make sure the voltage is present while pressing brake pedal.

Start by monitoring the voltage at the 2 green/yellow wires at the hazard switch. One comes from the fuse and should be +12 at all times. The other comes out of the switch through a normally closed contact and should be +12 at all times unless you operating the hazards. When operating the hazards the circuit opens and the voltage should pulse with the flashing of the lights.

Next, move to the brake light switch. There are 2 green/yellow wires connected with a normally open contact. The wire coming from the hazard switch should be +12 at all times (except when operating the hazards). The other should be 0 until you step on the brakes and go to +12 when you step on the brakes.

Next, move to the turn signal switch. There is a green/yellow wire, a white/red wire, and a white/black wire. These are connected with 2 sets of normally closed contacts. Each contact opening in only one turning direction. The green/yellow wire coming from the brake light switch should be +12 when you step on the brakes. The white/red wire is the left brake light. The white/black is the right brake light. When the turn signal switch is in the off position both should be +12 when you step on the brakes. When you select the left turn signal the white/red is disconnected from the brake light switch and connected to the flasher and the voltage will pulse with the flashing. The white/black wire remains connected to the brake light switch and should be +12 when you press on the brakes. When selecting the right turn signal the same conditions apply but the white/black wire will pulse and the white/red will be steady.

By tracing the signal through the circuit in this way you should be able to determine where the voltage flow is interrupted. If you find voltage at one switch and it is not present at the next there is likely a bad connection in between or a bad wire. To find this you will need to trace the wires along their routing and look for connectors to inspect, cuts in the sires, etc.

[Duffman]

Thanks, Beermanpete, good steps to follow!

[240260280z]

[Duffman]

Thanks, guys, found out that it was a simple problem of a faulty brake switch. When I originally tested it, it showed power through the switch when the brakes were applied, so I thought that the problem was elsewhere. Tried the switch again, going through Beermanpete's steps, and found the brake switch was working on an intermittent basis. Bridged the wires to the brake switch and the brakes lit up like they were supposed to! New switch ordered from RockAuto. Problem solved! Thanks for all of your assistance!

[beermanpete]

Cool. Intermittent problems can be difficult to find.

[Wade Nelson]

Nice!