Brake lights not engaged with running lights?

[chaseincats]

Hi guys,

Working on a 1974 260z and ran into another weird lighting problem.  The brake lights work as intended with the running lights off, but when the running lights are switched on, hitting the brake pedal does not brighten the rear lights.

I checked the bulbs and the brake light bulbs are indeed dual filament like they should be.  The odd thing is that when the running lights are switched on, both filaments are lit, that shouldn't be the case right (assuming one filament is for brake lights and the other is for running lights)?

Any ideas as to how to get the brake lights to engage with running lights on? 

[SteveJ]

Post photos of the inside of the sockets and the bulbs you pulled out of them. Do this for all the sockets in each taillight housing. Otherwise, all you will get here is speculation.

[chaseincats]

2 hours ago, SteveJ said:

Post photos of the inside of the sockets and the bulbs you pulled out of them. Do this for all the sockets in each taillight housing. Otherwise, all you will get here is speculation.

Will do - it's my friend's car so the next time I'm at his place I'll grab some shots.

[SoCalJim]

Hey cats, my 1975 280Z brake light wiring is very straightforward according to the description in my Factory Service Manual.  Power flows from the battery to the black fusible link, through the shunt, through connector C-6, through a 10A fuse (right row, center fuse), through connector C-2, through the stop lamp switch down on the pedal box, back through connector C-2, on to the Body Harness connector that’s outside/behind the passenger seat, and on to the connectors at each rear combination lamp assembly.  

Or more simply, from battery, through a fuse, through the stop lamp switch, and on to the brake lights.  Nowhere should it tie into the parking lite circuit, turn signal circuit, or hazard circuit.  You may have some creative wiring in your car to uncover and sort out.  I still have to double check my actual wiring harness to verify everything I just told you is correct.

good hunting!

Edited June 30, 2019 by SoCalJim
Minor grammar mistake

[dutchzcarguy]

If you switch your alarmlights a few times on and off.. it's might be possible they work again.. the alarmswitch has many connections involving the brake and direction lights cables..

A euro car's alarm switch has only 4 or 6 conn. a USA model has 9 connections..!  ( in a USA car the brakelight wiring go's through the alarmlights switch..)

[grannyknot]

2 hours ago, dutchzcarguy said:

If you switch your alarmlights a few times on and off

Hazard switch ?

[dutchzcarguy]

19 hours ago, grannyknot said:

Hazard switch ?

Yes..

btw.. i didn't look into a elec. diagram but know there are a lot of wires onthat hazard switch..?

[chaseincats]

Got an update for you guys:

It seems the brake pedal has somehow been switched around such that when it is pressed, the running lights (side markers included) all turn on.  When turning the running lights on via the combo switch and then hitting the brake pedal, all these lights brighten.

We've been studying the FSM but are coming up empty here.  Any ideas?

 

-chase

[dutchzcarguy]

Side markers that brighten when braking??  Hahaha… somebody has made some changes in the elec. cables and you must have side marker bulbs with double connections on back?  huh??? 

[SteveJ]

Most likely you have a single filament bulb in a dual bulb socket somewhere. That I why I asked you to take pictures of all of the insides of the sockets and base of the bulbs.

[chaseincats]

54 minutes ago, SteveJ said:

Most likely you have a single filament bulb in a dual bulb socket somewhere. That I why I asked you to take pictures of all of the insides of the sockets and base of the bulbs.

Alright, I'll ask him to send over pictures.  But do you mean that having single filament bulb where a dual *should* be would make a change as drastic as this to the way the car functions?

[SteveJ]

Yes, because you are backfeeding the circuit.