ST185 ignition-switched 12v power wire to tap under hood

EvilStig

New member
click for detail

I searched all over the internet and saw this question asked a lot but never categorically answered. Say you need to run some mod/accessory in the engine compartment only when the ignition is turned on, and don't want to run wires through the firewall... what's a reliable source of ignition switched power you can use?

The underside of the relay box next to the battery holds the answer. The plug in the drivers side rear quarter of the box has a blue/red wire going into it (blue with a red stripe). That wire will be live whenever the ignition is on.

The correct way to use it is to splice into the wire, and use it as the signal wire for a relay direct off the battery. That's what I did and what I recommend, although judging by the gauge of the wire in question you can probably run anything short of a compressor or high wattage lights off it without disrupting normal operation of the engine. probably. I didn't test this and as far as I will recommend, you shouldn't either.

*for 90-93 USDM Celica Turbo Alltrac, cannot guarantee it. Test with a voltmeter first before committing to butchering your wire looms, please.
 

sefiroxx

New member
Yes, you could tap direct, but if you are at that point where you are assuming extra, might as well invest in a relay controlled power strip now and provide capacity for those future toys.
 

alltracman78

Active member
IIRC there are some pins on the underside of the fusebox where those connectors plug in that will also work.
You can add a pin to one of the connectors and you don't have to cut any wires.
 
Top