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Turn signal too fast with added 1156 bulb

2008 Expedition.

I connected left and right rear-facing yellow light bar lamps to the front turn signal wires.

Each light bar lamp has a single filament 1156 bulb.

Instead of two, three bulbs are now operating.

Problem: The turn signals blink faster - similar to when a bulb is out.

On four-way flash they blink normally.

(I doubt LED 1156 lights are reflected well by the lamp reflector, so they would not work well.

Any ideas?

Thank you.

The extra load is most likely effecting the flasher unit.

Cougar is correct. It’s either go to a heavier duty flasher or do some home wiring with relays which will bypass the factory wiring.

Are you sure that you did the wiring right? If the flasher works the way I suspect it does, faster flashing would be due to higher resistance from the filaments. That would probably indicate that you have your new bulbs in series with the existing ones. I would think you would want them in parallel which would cut the resistance and probably lower the flash rate.

That’s all theoretical, not practical experience. Theory only gives correct answers when one really understands all the factors, and I’m guessing about some of them.

In any case, if you want the same flash rate you used to have, you might well need a different flasher.

Thank you all.

Each front turn signal wire now supplies power to two bulbs in parallel instead of just one.

I’ll try swapping the four-way flasher can with the existing flasher unit.
Anyone knowhere they are located? Manual does not say.

But ok4450’s suggestion of using relays is best.
That way I am not drawing double the load through wires designed to power ONE bulb.

In the front fuse box above the radiator there are two little unused trailer turn signal relays.
I’ll have to open a relay to discover which terminals are the contact and which are the coil.

(I could not merely tap into the trailer turn signal/brake light circuits.
The brake closes both relays - the yellow lightbar lights would also illuminate as brake lights.)

Thank you.

Just pulled the little cube relays.
Covers cannot come off.
Next to each of the four pins is a number:
Anyone know the meaning?

Update: I discovered that (1) and (2) are the coil pins.

Thank you.

As I recall the flasher checks the lamps by comparing load. You have the load out of balance and/or out of spec and it is just trying to tell you something is wrong.

May I ask why you did the re-wiring? a medical transport vehicle: blood, blood components, surgical instruments, implants, etc.

The back of the Federal Signal “Streethawk” light bar has two unused yellow lights which could be good turn signals. (If red I could easily connect them to the trailer wiring harness and make them brake/turn signal lights.)

Yes, only one bulb operating would make it flash faster.
Have never had a situation where additional load changed the flash rate.

This circuit is designed to allow addition of a mirror turn signal light, #906.
Is it LED which draws much less current?


I believe that your vehicle has an LCM (lighting control module) that controls much of the lighting circuits as well as others. If you keep working with the wiring on this car like it has a collection of flasher units scattered under the dash, you could easily toast the LCM and end up spending several hundred dollars to get a new one. (People have opened them up and soldered in new relays to replace the ones that gave up their smoke.)

Relay isolation is a great idea and the prescribed way to deal with LCMs. I believe that Ford sells Expys as police and emergency vehicles with extra wiring for lights. Depending on what you plan to do, you might want to get some wiring diagrams. It sounds like you might already have some of that data. That may be what the extra relay sockets used for if they are not used for options like the air suspension.

Federal Signal might help you out. An Expy board might also have useful information as lots of these vehicles are used for emergency purposes.

An LED uses less current than incandescent light bulbs so, yes, it can make a circuit think there is a blown bulb and flash fast if there is no bulb connected to the circuit.

This is just a typical Expedition XLT

I assume an LED 1156 would allow a normal blinking rate.
But such LEDs are very poor lights.
No light shines on the fixtureflector, which is made for a filament bulb, so mostly all that would seen is just a one inch “dot”.

I hooked up the two unsused trailer turn signal relays.
They draw so little current thathe blinking rate remains normal.
Just need to find an inline fuse and my soldering iron to connect the relays and have B+ connected to the the relays.

Thank you for your advice and warning.

The flasher is a thermal relay. Heat generated by flowing current causes a bimetallic part of the flasher to bend, opening the circuit and interrupting the curent flow. It then cools, reconnects and starts heating up again. Repeat.

Adding a light in series with the existing bulb causes a larger current draw. More current flows, the bimetallic part in the flasher gets hotter faster, and the light blinks more quickly.

The solution is to connect the new bar lamps off a totally different spot of the power bus, an unused spot on the fusebox. That takes it out of the existing bulb circuit and eliminates its effect.

Thank you.
Yes. Interesting that the bimetallic component also blinks faster when one bulb is out.
Apparently less current drawn through does not heat up as much and the metal wafer cools faster to the invert threshold and opens the circuit more quickly - to indicate that a filament is burned out.

These bulbs must be controlled by the same circuit as the blinking turn signal bulb.
I connected the two relays which switch B+ right to the bulbs.
So no extra current is drawn through the wire meant for a single bulb, and the relays do not draw enough current through the deeber to change its speed.

As a little boy I called it a “dee-ber” because it used to make that sound.

No it is not (thermal). It is electronic on this and almost any other car made now!

Odd, this
doesn’t look like a computer to me.
This is the actual 2008 Expedition part.

It’s not thermal. It’s electronic. It uses an IC specifically made for this application that has current sensing built in. I can look up the part and the internal schematic if you would like. Better yet, you should get one and tear it apart and see for yourself.
They stopped using thermal units many years ago.
The current sense circuit allows it to go into double speed mode whenever the current is out of tolerance (too high or too low). This serves as a warning to the driver that one or more bulbs are out. The old thermal units couldn’t do that. Instead, they would slow down or stop if enough bulbs were out. That was because not enough current would flow through them to heat the bi-metal strip up enough to snap the contacts open.

If you can find the link to the part I’d appreciate it. If I’m incorrect I’d like to know.

Yeah, I’m familiar with Kirchof (sp?) and the reciprical laws. two resistors in parallel equal less that a single resistor, and with current being voltage divided by resistance what you’re saying makes sense.

I don’t have access to the specific one used here at home. However I do have some that are pretty close. (BTW, The “EP” prefix for Tridon flashers seems to mean “electronic flasher.”)
This link gives reasonable (if somewhat outdated) descriptions of flasher types, including the electronic “hybrid” type used in this case.

This link give details of one of the newer chips (ICs) being used for automotive flashers.
This is an older, but more common one.
And lastly, here’s a schematic with some details on modifying the flash rate.

I don’t believe that Ford has used a thermal flasher for the last twenty years. In many cases, the electronic one used looked very similar to the old thermal unit. But that is changing too. Of course, many of their cars are now networked (“computer” as you called it), and don’t have a separate flasher module.


Thanks for all the interesting information.

I solved the problem by removing the unused cube trailer turn signal relays and connecting their coils to the left and right front turn signal circuits.
The coil draw is so low that they do not affect the turn signal rate.
Their contacts close and send B+ through new wires to the 1156 light bar bulbs.
I am not drawing the current of two bulbs through conductors sized for one filament.
Connecting them to the front turn signal circuits, they will not close when the brake pedal is depressed.

Cool. And I understand the schematics. And used the word computer incorrectly rather than IC.

However, the link I provided was for the actual flasher for a 2008 Expedition. I found it by looking up a replacement part for that vehicle. Its internal construction is not shown, but it’s clearly an old fashioned relay rather than an IC. Or it’s a very well disguised IC.

The important thing is that the OP got the problem solved.

We’re still not communicating correctly. I’ll take the blame there. The IC drives the electromechanical relay. The flasher module you show has inside it a big relay and a small IC (and a few other components). Look closer at the schematics provided and I think that you’ll find that each one shows a relay too. The IC provides the timing and current sensing. It drives the relay, and the relay provides the high power (and robust) switching for the lights.
As I said before, cut one of these open and see what you find. (A relay, an IC, and a few other electronic components. You won’t find a bi-metal strip.)