You are trying to HIGH SIDE SWITCH so you will need a PNP and a NPN.Like this;
If you have an Ohm meter, you can measure the coil resistance of your relay. The static coil current will be the vehicle's nominal system voltage, about 14.5 V when running, divided by this resistance. I'd expect the coil resistance to be something like 50 to 100 Ohms, so a nominal coil current on the order of 200 mA.One thing that follows from this is that a 2N3906 PNP transistor has specified performance to 100 mA, so you probably want to select a part with higher current capacity.
LED3 and LED4 are wired incorrectly, you cannot mix your 12 volt and 5 volt supplies in that way. The LED's need to be powered from the 12volt rail with the appropriately higher value resistor. You've also omitted the very necessary free wheeling diodes across the relay coils. The PNP transistors may/will fail in short order, depending upon the device type.PS: please don't promote bad schematic habits with Fritizing, like drawing diodes and ground symbols upside down. That software is a waste of everybody's time and energy. Either use a real schematic editor or draw them by hand which highly preferable over fritzzy silliness.
Why not power the LEDs from the Arduino pin through a 1k resistor - you are allowed to drive both atransistor and an LED from the same pin, so long as total current is within the limit. You only need onetransistor per pin to drive the relay.So pin -> 220 ohm resistor to NPN base, relay + diode between collector and +12V, emitter to ground. (This is the standard circuit to drive a relay, lots of examples out there).Add LED + its 1k resistor from the Arduino pin to ground.Much simpler, and saves 4 resistors and 2 transistors!
I tried to get the one trasnsistor setup to work but never could get the full 12v out of it, but I didnt have it hooked up quite the way youre talking about, Ill give it a try tonight.
Just hook up your relays to the Arduino using the ZVN4206A relay drivers. If you can't figure that out, I would be happy to make you a drawing.
Then go back to Ebay and buy a couple 12v auto relays with sockets. They are real easy to hook up.
I think the best free software to draw schematics is ExpressPCB. You can download both PCB layout software and Schematic software for free. All you need is the schematic software (but you will get both)
Then you probably were using the wrong circuit or not providing enough base current. Switchinguses the common-emitter configuration, and base current needs to be 5 to 10% of load (collector) currentwith a BJT.