[rasilverbird]

Sniper EFI calls for 12v keyed power while the ignition is on AND while the engine is cranking. Factory switches are only on when the key is on, and shut power off while cranking. What are you guys using for an updated switch that has power on for both?

I found a switch from American Autowire, but they say it's for a 55-57 chevy. Looks similar to mine though (in dash '68).

https://americanautowire.com/product...341268f1&_ss=r

My car does have a bypass wire that is on while cranking but not on while on. Doesn't seem like a good idea to splice this to the other one, but i'd have power both on and while cranking.

[Formulajones]

There is power with key on and while cranking with factory switches, you just have to find which wire.

Not only that but you have to find one that doesn't drop below around 10 volts while cranking. EFI really doesn't like it if it's less than that and causes hard start problems.

You'll have to grab your volt meter and start probing wires to find one that's hot with key on and while cranking and also watch the voltage drop.

Some GM will have a terminal right off the fuse box that's hot with key on and while crank and you can simply plug into that. My Chevelle is this way and works the sniper fine.
The GTO however would not, even though it had the fuse terminal it didn't hold enough voltage during crank so I had to probe ignition switch wires to find one to do the job.

[JLMounce]

When doing these systems, to avoid potential RFI issues, I recommend the use of relays to power everything up.

I have my FiTech system wired off an MSD 4 channel relay. The relay is triggered by the factory coil wire. I have the FiTech on one channel, the ignition on a separate channel, the ground trigger fan on a 3rd, then I also have a channel that is triggered by the accessory key on for in-cabin accessories. Your relay will provide a full 12+ volts during cranking, assuming your battery is fresh and sized right for your application.

[Gator67]

Originally Posted by JLMounce

When doing these systems, to avoid potential RFI issues, I recommend the use of relays to power everything up.

I have my FiTech system wired off an MSD 4 channel relay. The relay is triggered by the factory coil wire. I have the FiTech on one channel, the ignition on a separate channel, the ground trigger fan on a 3rd, then I also have a channel that is triggered by the accessory key on for in-cabin accessories. Your relay will provide a full 12+ volts during cranking, assuming your battery is fresh and sized right for your application.

Very timely...I've been thinking about doing this with a car I'm building. My worry was that the electronics in the solid state relay might create more RFI or some other issue. Do you split the single factory coil wire so that it goes to multiple 12v activation terminals?

[JLMounce]

Originally Posted by Gator67

Very timely...I've been thinking about doing this with a car I'm building. My worry was that the electronics in the solid state relay might create more RFI or some other issue. Do you split the single factory coil wire so that it goes to multiple 12v activation terminals?

Yes, I split the coil wire in my case for the three different channels. But you can do almost any configuration you could think of. As an example you could hide a switch on the ignition channel and use it as a theft deterrent to kill the ignition.

Lots of possibilities. And because you’re only using the coil wire as a trigger, you don’t have to worry about the resister wire aspect of things. There’s always enough current to keep the relay open.

These solid state relays also have burst amperage in them so if you’re using them with an electric fan, you aren’t blowing the relay as it powered up. If you need a lot of amps on something you can also run the relays in series to increase the amp capacity.