78 ford f250 crew cab issues

[chrisallison]

When I turn the left turn signal on or stap on the brake cab lights and side markers lights flash. I need help please I can not find the problem. I've changed all bulb sockets.

 

[DNFXDLI]

Checked your grounds and headlight switch?

Signal light switch can be an issue as well....have you used a test light with a good ground to confirm?

 

[chrisallison]

On the turn signal switch yes. I unplugged the harness that runs the lights on the bed and the harnesses that runs the lights on the front of the truck I have it isolated to the cab I've put a used headlight switch on thinking that was it but I guess it could be bad too. I'm hoping for some advice so I don't soak a ton of money into it and it be something stupid.

 

[DNFXDLI]

Here is a link to a troubleshooting book which might help...

http://www.fordtruckfanatics.com/forum/showthread.php?t=29167

Did you use the tester on those unplugged sockets?

 

[Fellro]

Turn signal switch and cab lights are not even in the same circuits and switches, but it is possible to have a wire that has shorted across. Do you have a plug for a trailer? When you say they lights flash with the brake, do they flash like a turn signal, or just get brighter when you hit the brake?

 

[DNFXDLI]

Do you mean clearance lights for the cab or inside lights?

 

[Fellro]

Good point... I was thinking clearance lights. Interior lights are still separate from any turn signal/brake circuit.

 

[chrisallison]

Yes I used the tester on the sockets. No plug for trailer and when running lights are off and you step on the brake all lights except for headlights come on and when you turn left turn signal on all running lights flash like a turn signal. And inside lights, clearance lights, side markers, and turn signal on left side.

 

[Fellro]

Sounds like more of a harness problem than anything. Try simply unplugging the turn signal switch and see what happens. It will help to isolate where you need to look. If you unplug the turn signal switch and it still happens, then you know without a doubt the turn signal switch is not the issue. I suspect you will find the problem somewhere in the wiring to the left tail light.

 

[1970Custom]

What bulbs are you running? Incessant or LED?

Reason I ask is I just upgraded to new high efficient LED in the tail lights on my DD and since then when I step on the brakes, I have the same issue...

 

[DNFXDLI]

Sounds like a ground off somewhere.

 

[Fellro]

That would be due to the low resistance of the LED vs incandescent... You have to be careful with the LED bulbs, as they can cause that. However, his is restricted to left side turn only and brake, which are common circuit to the left tail light only. So my thinking is that the tail/brake circuit and marker light circuit to the left rear tail light have gotten crossed up somehow.

 

[chrisallison]

I am using LED bulbs

 

[Fellro]

Ground at left tail light is potentially suspect as well, now that you say that. Feedback through the marker circuit.

 

[DNFXDLI]

I am using LED bulbs

Unless you have the dropper resistor built in or external, you will have problems with LED's...and good call Eric

 

[Fellro]

Try putting regular incandescents back in and see if the problem goes away. LED bulbs often require a resistor to compensate for the low resistance. Interesting that it only affects the left turn though.

 

[chrisallison]

What's a dropper resistor?

 

[Fellro]

It just adds resistance to compensate for the LED not needing much power to run. drop= volt drop, resistor is how it achieves said drop.

 

[chrisallison]

OK do you need to put them on turn signal and tail light wires?

 

[DNFXDLI]

What's a dropper resistor?

Parallel resistor to increase current flow to the circuit and path to ground....doesn't affect the voltage...there is a common connection on dual filament lamps (like 1157) which can be negated by an LED.