[couchflambeau]

Originally Posted by bzbuzz

after researching, my conclusion is that I dont think there is a way to make my defi's stayed on when i crank engine since i can't find solid 12v line that always hot. like i said eariler, all 12v lines drops when engine starts. this is not the issue w/ ign wire, but 12v line.

BS Private Pyle.... you're not lookin hard enough...

If nowhere else... go to the ignition column... there WILL be a wire there that goes +12v with the ignition on and holds it thru the crank cycle.

Find your make and model here and wire to the 1st ignition wire....

Subaru Wiring

If your vehicle isn't listed, should be a heavy gauge green wire at the column... meter it first to verify.

Leave your radio on the accessory lead... that's where it belongs.

[wi77iam]

Originally Posted by bzbuzz

after researching, my conclusion is that I dont think there is a way to make my defi's stayed on when i crank engine since i can't find solid 12v line that always hot. like i said eariler, all 12v lines drops when engine starts. this is not the issue w/ ign wire, but 12v line.

That's why I said to check your battery. You probably have it wired right, but if your voltage drops when you crank enough to cut out the defi's, then a more powerful (and fully charged) battery may help. Otherwise, look into a voltage regulator or a tank circuit, which is a small second battery that switches in when you crank.

My car PC is a lot more sensitive then your defis to power fluctuations, and it survive a crank very well.

[Rootus]

Originally Posted by wi77iam

My car PC is a lot more sensitive then your defis to power fluctuations, and it survive a crank very well.

Any decent car PC power supply should be able to regulate voltage when the input varies between 6 and 30 volts. It's unlikely the Defis have anything that good.

[imthaye3]

Because of the chemistry in the battery, when you try to crank (demanding 200~300 Amps depending on the engine temp. - lower temps need more current) the voltage drops to 7~8 Volts, or maybe even 4~6 volts if its really cold, for half a second or 1 second. ECU's that have to remain turned on (most ECU's turn off below 8 Volts) during cranking are on a circuit with a DC/DC converter.

What you can simply do is add an Aluminum Electrolytic Capacitor (rated: 10,000 uF on 35V or 50V) or higher capacitance or voltage. Make sure the polarity is correct. The capacitor should supply your gauges for 1 or 2 seconds which should be enough (the radio should be turned off during cranking), if the problem keeps going then your battery should be replaced because if the voltage is staying low for a longer time (more than 1 second) then this is a battery or starter problem. But hope its a battery