In the engine bay, where is/are the best wire(s) to tap into to get a power when the key is in the on position?

 

This has been covered many times, a search would have revealed the results.

Anyways, by your trailing ignition coils is a green six pin connector, the black wire with white stripe has ignition switched power. Use it to switch a relay and power the device straight from the battery using the relay.

 

I'm aware of that one. Is that the only wire recommended for switched power in the engine bay?

 

I don't know if it's the only one, but it's probably the only one I'd trust. That 6 pin terminal is for a test light to pull codes (blinks for different errors). The +12V is constant with ignition and the grounds are pulsed on two of the other terminals to blink specific patterns and tell you what is wrong. Since the terminal is almost never needed for this purpose, I wouldn't worry about drawing current from it for a relay.

Any other ignition switched power source under the hood probably has an intended use, and I wouldn't mess with them so something else isn't disrupted by mistake. Not saying it will definitely happen, but I just wouldn't want to risk it myself when there is a perfectly good unused source at that handy 6 pin connector.

You can try using a multimeter to test the unused fuse sockets and see if any of them receive a switched +12V. That would be a safe, convenient spot to tap into.

 

The Leading Coil has a single wire test connector. You could use that one as well.

 

I need to run a number of relays in the engine bay. In that scenario, if I only have 1 or 2 switched wires to use, -- say I have 10 relays I need to run, how would I wire them up to 1 or 2 switched leads? (assuming splicing them all in directly to the 1 or 2 switched leads is not recommended)

 

Im not an electrical expert, so take this with a grain of salt.

 

What are you trying to run with multiple relays..or why do you need to run many relays?..
For instance,I ran relays for my 4 light headlight setup but I used the Switch for relays and the battery to power the lights,rather than have the lights get routed through the switch and burn it out.
If you went aftermarket ECU and left the Fuse Block in the engine bay then you can use some of the now defunct circuits to pull power from and they are switched..like the EGI fuse.

 

Y, need to run relays for much of what you mentioned above. I've got a dual-headlight setup, driving lights, aftermarket ecu, injectors, water injection, electric boost controller, electric fan - that's 8 relays that I can think of without popping the hood to check for sure.
..and even using 2 relays for the dual headlights, I burnt out my headlight switch but that was because I used higher power incandescent bulbs instead of leds.

I've left the fuse block in the engine only because I haven't had time to fully investigate all of the electronic circuitry that is no longer in use. Main engine wiring harness is gone, but much of everything else is still in there. Since it's all 30 year old wiring that's had to deal with turbo under-hood temps, I feel better just running new wires and relays--but I definitely am inexperienced with this so if you have better ideas, let me know.

 

I would ask Chris Ludwig in the Haltech section about any of the engine stuff.
The headlight stuff as I said is cake..you take the power for the coil section of the relay straight off the 3 pin connector for the headlight(the bulb connector)..power for actual lights off the battery.Use one relay for low,one for high,split the ground.It doesn't activate or draw until the lights are on.