Turn signal & brake light problem

[richard5933]

I've been trying to solve a problem with my turn signals & brake lights on my 1964 PD4106.

Here's what happens:

Right turn signal works great. It blinks with or without the brake lights.

Left turn signal works great on its own. Problem comes with applying the brakes. Usually, when applying the brakes, the left turn signal will continue blinking but the brake lights will not. On rare occasion the left turn signal and brake lights will function simultaneously, but even then the brake lights will stop after just a few blinks. The telltale light for the brake lights will fade away after a few left turn blinks.

I've already changed the turn signal switch with a brand new one from Luke. Wiring in the engine bay has been thoroughly inspected. Other than a few lamp socket we replaced all looks good. We removed the old wiring harness from a toad to be sure it wasn't causing problems. Rechecked where it had been connected.

Possibly the turn signal blinker. I'm not sure if it could cause such a problem, especially since the blinker is a newer one and blinks fine without brakes. Since the same lamps function as both turn and brake lamps, possibly?

The brake light telltale fading away instead of just turning off leads me towards something like a minor short causing or a self-resetting breaker acting up? The intermittent problem makes it quite difficult to locate as well.

Any advice would be greatly appreciated. Right now, I have to decide if it's more important for drivers behind me to know that I'm turning left or that I'm stopping. Something that most likely won't end well in an emergency situation.

Richard

[richard5933]

I've been trying to solve a problem with my turn signals & brake lights on my 1964 PD4106.

Here's what happens:

Right turn signal works great. It blinks with or without the brake lights.

Left turn signal works great on its own. Problem comes with applying the brakes. Usually, when applying the brakes, the left turn signal will continue blinking but the brake lights will not. On rare occasion the left turn signal and brake lights will function simultaneously, but even then the brake lights will stop after just a few blinks. The telltale light for the brake lights will fade away after a few left turn blinks.

I've already changed the turn signal switch with a brand new one from Luke. Wiring in the engine bay has been thoroughly inspected. Other than a few lamp socket we replaced all looks good. We removed the old wiring harness from a toad to be sure it wasn't causing problems. Rechecked where it had been connected.

Possibly the turn signal blinker. I'm not sure if it could cause such a problem, especially since the blinker is a newer one and blinks fine without brakes. Since the same lamps function as both turn and brake lamps, possibly?

The brake light telltale fading away instead of just turning off leads me towards something like a minor short causing or a self-resetting breaker acting up? The intermittent problem makes it quite difficult to locate as well.

Any advice would be greatly appreciated. Right now, I have to decide if it's more important for drivers behind me to know that I'm turning left or that I'm stopping. Something that most likely won't end well in an emergency situation.

Richard

I did some research in the manual and have two theories...

The stoplight relay controls stoplights. If a bulb is blown the telltale won't light. Since the stop lights do double duty as turn signals, when they blink the relay reads that as an intermittent bulb outage. To allow both stop and turn lights to function, a resistor is placed in the circuit during turn signal usage.

I'm thinking that the problem is either the stop light relay or the resistor. Since the resistor appears to be working properly on right turn signal usage, I'm leaning towards the relay or wiring between.

Anyone else been here before?

1964 PD4106-2412

[chessie4905]

Check the ground connections to the lights in question.

[daddyoften]

No on having the same problem but I agree with checking ground,  a bad ground can cause all kinds of weird problems.
Eric

[richard5933]

Found more than a few problems, but they all resolved around loose/bad connections.

- I replaced all the light sockets for turn/stop lights. There was enough corrosion that the ground wasn't solid.

- There was a loose ground wire going to the lights on the fiberglass rear engine cover.

- I went through both the drivers electrical panel and the main electrical panel and tightened every connection that needed it. There were more than a few.

Apparently the stop lights on the 4106 will not light the telltale if there is a bulb out. When the turn signals are used, a resistor is used to replace the blinking bulb(s). Any type of a ground or connection issue is read by the stop light circuit as a blown bulb, and this results in no tell tale light. I'd been fighting this for a while to fix a problem on the left side.

Odd thing was that after I got everything up and running and working properly, I wrapped the wiring with black tape. Then I tested again and found the right side was acting up. A butt connector was slightly askew, and this was enough to cause the problem.

Richard

[chessie4905]

Consider soldering these connections and double shrink wrap with second piece overlapping first piece or use butt connectors that have the sealant in them.

[Fred Mc]

I had a similar problem on my 4106. On our last camping outing my wife(following in a car) noticed one signal light was quite dim.I solved the problem by replacing the rear tail/signal/brake lites with all new LEDs and of course wiring. They are not only more reliable BUT also a heck of a lot brighter. I now had a LOT more confidence that cars following will know my intentions a lot easier.

[richard5933]

Thanks for the additional comments. I was able to get the problems solved on this bus, mainly through checking and repairing ground connections and replacing the light sockets.

For those not aware, this bus was totaled in a collision last fall. It was recently sold at auction and I understand that its parts will be used to help keep other buses on the road. So, obviously I will no longer be working on it.