constant power while cranking wire?
 

im hooking up my digital boost guage and i need a wire that when the car is off, the wire gets no power. but when you go to start the car, it stays constant WHILE cranking. it needs this to go through a zeroing out process. so where most power cuts for a split second while the car is cranking to start, i need a wire that becomes, and stays live.

if i dont have this wired properly it will not properly read boost and give a false reading

thanks!

The ignition circuit is powered like that. If you tap into that I would recommend using a relay. That source is near the brake booster. An in cab source is probably available but I don't know where.

Ignition 1 circuit, black/white wire coming off the ignition harness. it's on one of the first pages of the wiring diagrams.

https://www.rx7club.com/attachment.p...1&d=1269275746

Strip off about 2 inches from the wire as it comes off the ignition harness. Use good strippers or a razor blade if needed, but don't cut the original wire. Take your power wire for the gauge and strip off about 2-3 inches from it so you have a lot to work with. twist and tape securely. Use good quality tape, either the self-fusing kind or regular style tape (I prefer 3M, you can get it from Advance Auto). You could solder but you'd have to be really careful because of the gauge of the wires you are dealing with. You'd have to heat up the wire really well with a good gun or you could have a cold solder joint. You could do more harm than good by soldering--I personally wouldn't do it, as I don't solder splices to the ignition harness. If you stripped off enough wire from each, you should be able to twist it securely enough that it will never come loose.

You won't need a relay for what you're doing, it's like 10 or 12 gauge wire. It can power a lot. Ignition harness wires are used on many professional installations of aftermarket alarm systems.

I understand you have a digital gauge but maybe don't understand completely. Why wouldn't the normal switched power source (circled below) work? There's probably some power draw when actually cranking, but it doesn't "cut" power.

http://img535.imageshack.us/img535/4...ox002mediu.jpg

The extra slot key on power in the cabin fuse box does cut power when cranking. I tested it with a meter when I was sourcing a place to power relays.

Then I stand corrected.
A power 'cut' isn't apparent on my more traditional gauge. The indicator makes a sweep when I turn the key on and then 'zeros' itself. Since it doesn't do that a second time after cranking (at least I never noticed it), I assumed power was constant.

so pretty much anywhere i can grab one of these wires will be ok for what i need right?
http://i166.photobucket.com/albums/u...ub/hotwire.jpg

yeah. you can use a test light or a multimeter first to verify that it is getting power during cranking

only problem with that is that my car cant crank right now. in the middle of a project and trying to do somethings while i dont have access to a welder machine. so i cant test it. thats why im double checking.

it doesn't matter whether the starter is in or not. put the key to the start position and the ignition 1 and start circuits will be hot.

so its this black with white stripe wire here right?

http://i166.photobucket.com/albums/u...b/DSCN0343.jpg

http://i166.photobucket.com/albums/u...b/DSCN0340.jpg

yes, no, maybe? :P

Test it

I am doing a similar install with my AEM gauges. They need a constant while cranking power source that is also switched so they power down. In the drivers kick panel fuse box you can tap into the fuel pump 20A fuse (top row, 2nd from the right). It switches on with the key to provide voltage and is obviously on while cranking.

I was a little worried about "taking" potential power from the fuel pump, but the gauge only requires 1/10th on an Amp to run.