battery switch

This isnt necessarily a tacoma question but you guys are a fountain of knowledge. On my second car (e36 m3) i put in a start button with a relay and an ignition on/off switch to eliminate the use of my key and ignition cylinder (except for the security feature). whats making me nervous is the fact that i didnt use a relay for the switch. Its a 35amp switch but id still like to add a relay in there so the switch wasnt bearing the entire load straight from the battery. How would I go about adding a relay in there?

 

I need to picture this in my head right.

At the moment you have battery-ignition-relay-starter, right? And you want to add a relay between battery and ignition switch?

You don't need one unless the ignition switch has other electrical components drawing power through the switch. Or, am I not understanding your setup?

 

So there are two parts. There is the button to start the car and that has a relay connecting the harness, a button to start the car and the ignition cylinder. Then there is the switch to turn on the accessories (like turning the key but not firing the car up). That comes straight from the cars harness so its got a pretty decent amount of amps running thru it. Doing my research online i found this. "Wherever manual switching has been used for direct switching of a Lamp or Motor or any gadget exceeding 10 Amps of load, a suitable relay must be put in the circuit." so there is a heavy load and using a relay will make it so the full amperage of the motor isnt running thru this single switch in the dash. I just need to know how to correctly set up the relay in the circuit. Make sense?

 

Gotcha.

Before doing more wiring, I would measure how many amps are actually going through the switch. You may be fine with the switch. If not, it will tell you what relay rating to get.

A four-pin relay should be sufficient. See diagram below.
Pin 85 is grounded; pin 86 goes to your switch. The relay will take less than 2amps to operate; so 18AWG wire can be used for both pins.
Pin 30 goes to the battery or full power source; pin 87 goes to your accessories. AWG rating should be about 20% above the amp requirements, probably 10-12AWG.

These are called Bosch relays but there are other similar designs. I've used this style to wire aftermarket horns. I've used the solenoid style to manage power from my truck's 2nd battery to a power fuse block, a Cole Hersee # 24059.

 

This is great. The only other question i have is where does the other end of the switch get hooked up to?

 

Pin 86 is power source from your 35-amp switch.

If I understand your setup, you are currently using a 35-amp switch to power your accessories. There is battery power going to that switch at one end, and out to the accessories wiring at the other end. This end gets re-wired to Pin 86 and Pin 87 now directs power to the accessories wiring.

The 35-amp switch is now overkill; you can remove it and insert a switch rated 1-5 amps.

BTW, Pins 86 & 87 are interchangeable. Either one can get power as long as the other one gets grounded.

 

now im confused again sorry. I drew a picture to help. The power from the wiring harness is going into 30. Then 85 is the ground. 87 goes to the ignition cylinder because that is where the power is going to. and 86 is the switch that will turn on the relay. Is that correct? so what do I connect the other end of the switch to?

 

Pin 30 is power from the battery. The switch at Pin 86 is powered from the harness. The switch is not grounded; if the switch has a ground connector, it's because the switch has a light and the ground connector is used to light the bulb. Otherwise, when you flip the switch, it would be connecting positive to negative and that would be bad.

What the relay is doing is allowing low amp power via Pins 85 & 86 to power a high amp hungry device via Pins 30 & 87.

 

The switch has three prongs. Power in, power out, and ground because its lighted. But now youre saying I need two power sources (one from the ignition wire in the harness and one directly from the battery)? My current set up is I took an ignition wire in my car going to the ignition cylinder and cut it, adding in a lighted switch with a ground. Now I want to add a relay in that setup so the switch isnt bearing the entire load of the cars ignition. The switch is replacing the need to turn the key on to get power to the car but not turning it completely to actually start the car up.

 

You can draw power from either source, but drawing from the harness negates the full potential of the relay should there be a high power demand because the harness wiring is, what, 18 AWG wiring?

And I don’t think your switch is bearing as much load as I think you think it is. Power is being sent to other relays that are bearing most of the load. That’s why I suggested measuring how much load the switch is actually bearing. You can use a relatively affordable multimeter to do that. There are numerous videos on youtube; this one is simple and direct: https://www.youtube.com/watch?v=5xMDWzUPk_w

 

Monday night I will dive into the car and get back to you with my multimeter measurements but thanks for the help so far!