The Stovebolt Site Forums The Shop Area The Electrical Bay Trouble switching from incandescent to LED taillights

My 1952 3100 truck was long ago converted to 12v, and all the lights worked well (incandescents). But to get authentic looking reproductions and bright light I chose LED taillights from LMC motors. The old taillights were just trailer lights with three leads: running, brake, and turn signal, powering one single filament bulb and one double. They were activated by a toggle under the dash. Ugly but worked!

The LED taillights are three leads: running light, brake & turn, and ground. I changed them out (including the LED compatible flasher) and connected the wires according to the diagram (brake and turn sharing a lead), but now I have running lights and brake lights, but the turn signals both blink at once. Taillight manufacturer told me the toggle wouldn't work and I replaced it with the steering column clamp-on unit from LMC with the same results.

Incidentally the new turn signal switch has an emergency flasher which works fine, as do the front turn signals (incandescent).

Any advice for the amateur electrician?

Make sure your grounds are good and clean. Maybe add a ground to each light housing.
Make sure that you didn't cross wire the turn signals.

I assume you replaced the flasher with an electronic one that is designed for use with LED's. LED's typically do not provide enough electrical load for a traditional flasher to work properly. Your 4 way works because both front incandescent bulbs together provide enough load.

Thanks, but yes I changed to the LED flasher

If you provide the part number and vendor for the LED's and for the turn signal switch, I will help you wire it up. I don't know about issues involving mixing LED and incandescent. I don't know how many flashers or what kind are necessary with mixed types. I can help you wire it according to the instructions. I believe you don't have a ground problem if hazard works and front turn signals work. So this points to LCD/turn signal switch miswire or flasher issue. If the front lights flash OK and the rear LED lights flash OK during hazard mode, it then seems that flasher is OK and that points to miswire.

So if I can study the parts you bought and instructions, I can verify wiring with you if you wish.

I agree with bartamos, sounds like left and right rears are shorted together or wired together. I built my turn signal system using the three wire original turn signal switch. I am running single 1157 bulbs in the rear and single 1156 in the front. I added two DPDT relays under the dash. The turn switch activates a relay, one for each side, the original flasher can handles the job. All new wire to the rear and all original wire in the front.

I don't think there is a three wire turn signal switch in this world.

Tim, to whom is this question directed?

To whomever might be interested in a flasher with three leads.

Here is one that I have used with LED bulbs.

bartamos, I know it's sounds fictitious but the turn signal switch that was on the column is a three wire switch. I believe it was a dealer installed item but I can't say for sure. Mine is a 1957 big bolt, 12 volt from the factory. When I bought it there were remains of two running/brake lights and two turn signals on the rear. The turns were totally independent of the run/brake circuit. I replaced all of the cobbled lights and ran new wire to the rear and have two modern medium duty truck tail lights with run/brake/turn in one unit that uses a traditional 1157 bulb. The turn signal switch has one input and two independent outputs. I wired two DPDT relays so I could use the front fender mounted signals as turns and use the rears as run/brake/turn. It works like a dream and I wanted to keep the original switch - and it's a self canceling switch. I mounted clearance/marker lights on the grain box to meet DOT regs and I run those through a separate toggle. I still have to wire my mirrors for lights and heat but have not decided on where to run the wiring yet.

OK. Thanks. I have seen a 3 wire clamp on, self cancelling pseudo turn switch usually used on Willys. It thru me when you said original. In 57 there was a factory, column integral, 6 wire switch. No relays.
The switch, you evidently have, was not intended to have relays. It was for two separate rear lights on each side. It flashes front and rear left.,,,,and flashes front and rear right. Then, in the rear, you would need another set of lights for Brake and Run. A dual filament in each. The brake is not thru the turn switch like a normal setup. That same self cancelling switch is available as a normal 6 wire.

In order to only have one light on each side with that switch, you use relays. As you have done. The DIY wiring diagram for that is quite ingenious. I have it somewhere.

Yup, when I ran across the wiring diagram on the innerweb I new I had what I needed, I like electro-mechanical 'cuz I can fix it when it's broke.

Thanks everyone for your help. When it stops snowing here I'll spend some time on the truck. Bartamos, I tried to private message some of the details you asked about, but the system says your private messages are full, So ... I'll try to add photos to this reply. Im not much better at this site than I am on electrical....

Sorry about that. I fixed the PM.

OK, here is what I have. You either have it wired this way or you don't. Again, I'm not commenting on LED's or their Flashers. Just the wiring.
When you review these diagram pictures and start checking your work, DO NOT approach it as though you know you did it right. Approach it with "something is wrong and I HAVE to find it". Study the diagram and your wiring with great care. You know there is an error or malfunction. Make sure to notice on the diagram that some wires are to headlight switch and some are to turn signal switch........and others are elsewhere.

I used the words "brightest filament" and "less bright filament". This is in case of dual filament incandescent bulb. The LED light is already set for that.
The "third wire" is the ground wire on the LED, as you know. For incandescent, the ground is "intimate contact" between bulb base and socket.
I don't know if you have LED in front or not. Just making in clear for anyone searching in the future.

I thought I posted earlier, but apparently not. My lights are working now, thanks to Bartamos' diagrams and my brother in law. He trains mechanics for a living, and found the cross-wire in the rear end. In addition I had a couple of wires at the tailgate that were not needed but apparently fed the old taillights. My understanding is still hazy but the lights are bright!
Thanks, all.