first shot at relays

This is my first try at using relays, but I would like some help and input.  The schematic below is part of a vehicle wiring harness I'm attempting.  This is just the start and power buss section.  Basically, it is a NO momentary start switch that when pushed from a power off engine off state should power the buss circuit and energize the starter until released.  At that point, power should remain on at the buss and the tach signal disables the starter as long as the engine is running.  Pushing the button a second time powers down the buss and kills the engine resetting the system.  Thanks for your help.

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Jim

Well, just started proofing the sketch and realized the terminals are reversed on the battery...duh, sorry.

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Jim

Just looking at it briefly, first thing that I notice is the tach signal being used to drive a relay- you won't be able to use that, because it won't have enough drive. You might want to use some other signal, maybe like fuel pump power. Most cars have it set up to kill the fuel pump power when the car stops running, which sounds like what you need for the signal.

Not sure if the on/off setup would work-

The power latch relay on the top right looks like it'll be energized when you first push the start button to turn on the power, and open up the connection to the battery. It'd be kinda timing critical that the relay deenergizes first before the relay to the left releases, to remain latched. Unless you get it set up to make sure one relay acts faster than the other, it might just unlatch.

You could add a delay to one, but then you'd have a problem at the opposite end when you try to turn off, because then it'd stay latched when you wanted it to open up.

Thanks for the input.  I considered using the alternator for an engine run signal, what do you think?  I worry about the timing issue as well.  I will play with a delay and see how it works.

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Jim

Alternator might work if you can find a suitable point to tap into.
Some remote starts use a voltage threshold to determine if the car's running; so that might be another possibility.

Hopefully you can see this better.  It is a little simplified as well.

Thanks

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Jim