Source of switched 12v in the front fuse block?

[s5uewf]

I finally figured out how to eliminate my CIS fuel electrical circuit, and have the engine running when tapping into a constant 12v source. However, I need to tap into a switchable 12v source in order to be able to turn on and turn off the ECU via the key.

I've discovered a problem:
- the several fuses nearest the windshield are constant 12v and great for testing.
- the several middle fuses "appear" to be switchable 12v, as they produce 12v when the key is ON and no voltage when the key is OFF.
- However, when the key is turned all the way to START and the starter is spinning, all these middle area fuses stop providing power until the key is back to ON. This is defeating me at the moment, since I can find no other sources of switched voltage in the front trunk area.

Can anyone suggest or identify a switchable 12v source in the front fuse area I can use, please?

Or, is there another way around this - installing a small relay just for this ECU low amp 12 v lead, for example?

[billjam]

This might help. Terminal 15 from ignition switch provides power to fuses 7 and 8 in ignition and start positions.

[s5uewf]

I will give this a try. Thanks Bill!

[s5uewf]

Bingo! Tapped the ignition bus you highlighted and it works fine.
All the CIS wiring from the dash bulkhead back is gone and the EFI is completely wired, fused, relayed, etc.

Once I get a moment I'll document how I wired in my EFI in case others can take advantage of the info on how to wire the ECU into the ignition and how to energize the fuel pump relays by splicing the ECU fuel lead into the blue leads on the relays.

[jpgroth]

Originally Posted by billjam

This might help. Terminal 15 from ignition switch provides power to fuses 7 and 8 in ignition and start positions.

Does this apply only to the turbos? Looking in the fuse panel for 12v switched in my '79 SC for my EFI switched power

[s5uewf]

Josh here is a map I found on the 911 forum for an SC. It looks to be the same more or less. Ignition switch manages 4,5,6,7,8. 5,6,7 look like 25Amp fuses.

Fuse diagram

[DaytonaCoupe66]

Hello; I've run an AFR and Voltmeter guage wiring to the front fuse panel, and would like to 'tap into' the switched fuse circuits as per the pics/drawings. I have a 5 amp in line fuse for each. I see that power comes into the fuse panel via the top, and when I turn the key and put a test light on I get power at the top and bottom poles of the switched circuits.

Question: Does it matter whether I tap into the top or the bottom pole for the in line fused power to the guage(s)?

I can find a ton of pics and write ups for blade fuse panel 'add a circuit', but scarce info on our bullet fuse setup beyond ....tap into the front panel....

Opinions? Thanks!

[DaytonaCoupe66]

I tapped into the top of fuse 4 with a separate 5 amp fused link for each guage, middle panel, which is the cigarette lighter.

[fourblades]

Great info in this thread. I'm going to need to power my EFI and similar gauges the same way.

John