I am hoping I can get some help.
I am trying to install turn signals and hazard lights on my 1948 Chevrolet panel truck, The turn signal switch I have is only three wires. Can someone help me with trying to figure out my wiring schematic?

I have 1157 tail lights and with 2 wires. I cant seem to figure out how to incorporate the turn signals and hazards.
I also purchase a 5-pin relay but dont know where that would be placed in the schematic

Any direction would help.

The wiring really gets tricky with a 3 wire controller. I'm not even sure it can be done without at least adding some diodes to the wiring. The relay might help but I am not sure how that would factor into the system.

The limitation is that you want the brake light filament to also serve as the turn signal filament. Remember that the other filament has to serve as the taillight. You want the brake lights to come on whenever you press the brake whether or not you are using the turn signals. But you want the turn signal to interrupt the power to one of the brake lights when you use that direction's turn signal while braking.

Your turn signal switch will only send power to either the right or left turn signal when you move the switch to signal right or left. So you cannot wire the switch upstream or downstream of the brake light switch because it will stop the power flow to the brake light filament. If you wire it in parallel it will not flash the turn signal when you are using the brakes.

Your situation is even more complicated because you do not have a separate wire for the front and rear turn signals.

This is the reason they created 7 wire turn signal controllers. Those have an internal set of contacts that coordinate the turn signal/brake light function. I strongly suggest you save a lot of time and frustration and get one. It will be the best $30 you spend. Remember that the flasher has to match the voltage of the vehicle. Because you are using an 1157 bulb I assume you are converting to 12 volts.

7 Wire Turn Signal Switch

Rusty 37 Master nailed it. A 3 wire switch does not share the brakelights. You need separate bulbs with that 3-wire switch.

Diodes wont get the job done. It is an interesting technical problem if you think about it. One light needs to keep flashing when you step on the brake. There needs to be some active switching.

They do make little black boxes to connect Asian cars with separate signals to trailers. Trailers typically combine the signals with the brake lights. One of those boxes might work, although in my experience the reliability is horrible. They also dim the bulbs a little.

4-ways add another level of complication.

Thank you for your input. It has been driving me crazy because I was trying to figure out how I could get it all to function. For what its worth I cam gonna see if I can use one of the CURT 58240 Non-Powered 3-to-2-Wire Splice-in Tail Converter. See what happens I will post my results this weekend. Again thanks for the help .

https://www.amazon.com/CURT-58240-N...rter+58240&qid=1572387922&sr=8-5

I understand your thinking and agree that it might work. I have used a converter like that to connect trailer lights to a car that had independent turn and brake lights. That little black box is really a set of diodes (as I noted in my earlier response).

My suggestion is that you need initially wire the car as though it has independent turn and brake lights. The front turn signals have to be in the circuit after the turn signal switch and wired in parallel with the converter. Then add the brake wire to the converter and connect to the dual filament bulbs in the taillights. Basically you are making the car taillights function like trailer taillights lights.

Here are 2 things to consider.
- Do not try this with LED bulbs until you can get it to work with regular filament bulbs (which I think you plan to use). There are lots of instances when the low current draw of LED bulbs is not sufficient to make electronic devices work.
- The device might not work if there are no bulbs on what is labeled the "car" side of the converter. While it is a promoted as a "non-powered" device that simply means it does not need a separate power feed into it. It still requires power to work. The power comes from the turn signal and brake light functions. If there is no load upstream of the device it might not work.

Let us know what happens.