Weird Brake/Reverse Light Issue

[Falbz]

I am having some issues tracking down a brake light/reverse light issue on my 70 Cuda and it has me stumped. Pretty much everything works now on the car except the right brake light when you apply brakes (running lights they both work) and right taillight with the hazards on (left one blinks, right ones out). I also noticed that each time I apply the brakes my reverse light on the dash lights up very dim and not as bright if I put the car in reverse. When I put the car in reverse the dash light lights up nice and bright.  With the left turn signal on it causes the left reverse light to blink with the light (not as bright but very dim) than as it flashes it lights up the right reverse a little.  It's a nice little light show lol.  Right turn signal is fine. 

I just recently installed a new TW7 switch and flasher next to the ash tray which solved my turn signal issues. i am Trying to figure out if its in the rear taillight harness or somewhere with the dash harness. Pinch wire somewhere? Any help would be appreciated as I have read a lot of threads on the boards and am still stuck. I have the service manual and can't seem to figure how everything works in the wiring diagram.

Thanks in advance

[Jamiez]

The harness for the rear lights, connects just behind the driver side kick panel.  I recommend disconnecting it and using a voltage meter in combination with the controls (brakes/lights/turn signals/reverse) and seeing what voltages you have.  That will tell you if you are sending the right power on the right wires to the rear harness.

That should tell you if the problem is in the dash area or in the rear harness. 

My best guess is you have two wires making partial contact, probably in the rear harness where some insulation has worn...but that's just a guess.

[Falbz]

The harness for the rear lights, connects just behind the driver side kick panel.  I recommend disconnecting it and using a voltage meter in combination with the controls (brakes/lights/turn signals/reverse) and seeing what voltages you have.  That will tell you if you are sending the right power on the right wires to the rear harness.

That should tell you if the problem is in the dash area or in the rear harness. 

My best guess is you have two wires making partial contact, probably in the rear harness where some insulation has worn...but that's just a guess.

Thanks - that is what I was thinking too.  I'll use a volt meter again on the connector and see what's going. I picked up a new rear harness from classic and may just throw it on and see if it fixes the issue.

Do you know where the reverse light on the dash and wires from reverse light switch on the trans run exactly?

[Jamiez]

There is a harness that runs from the trans and into the bulkhead on the fire wall.  It also has a single spade connector which goes through the firewall and connections into the back of the reverse light harness that runs to the light on the dash.  The harness looks like this:



It connects into slots 7 and 8 on the bulkhead (at least in 74)

[Falbz]

Perfect - thx again for all the help and the diagram.  Ill mess with the car tomorrow.   

[Jamiez]

Good luck!  If all the harnesses look good, start checking grounds...ground in these vehicles is a pretty common cause of electrical gremlins.

[FY1Cuda]

Check the ground on the right taillight bucket (by connecting a jumper wire from the bucket to a marker bezel, gas filler, or trunk lock).  Also check to see if the taillight and brake light wires in the socket got reversed.  The socket has a little disk in the bottom with the two wire ends protruding.  If the disk is pulled out of the socket, it can sometimes be put back in 180 degrees off.

[HP_Cuda]

I was also going to say ground.

I did this on my other classic car when both rear tail lights were very dim. Now they are super bright after cleaning the contact points and tightening them down again!

[Falbz]

Check the ground on the right taillight bucket (by connecting a jumper wire from the bucket to a marker bezel, gas filler, or trunk lock).  Also check to see if the taillight and brake light wires in the socket got reversed.  The socket has a little disk in the bottom with the two wire ends protruding.  If the disk is pulled out of the socket, it can sometimes be put back in 180 degrees off.

Hmm interesting I will have to check that out.  Would have never thought of that. As far as the grounding issue would I still have this issue if the running lights work and turn signal light up as well.  Can i still have a bad ground as one filament lights up and the other doesn't 

I am very curious to check out the socket - Thanks everyone for the help

[Chryco Psycho]

 
 ground problem the lights may be grounding back through the reverse light on the dash

[73EStroker]

  ground