Live feed needed for aftermarket ECU

[Turn & Burn]

Must be a few of you that have come up against this....
I need a live for the ECU that doesn’t power down during cranking. It seems all feeds from the ign key cut whilst the key is turned to the cranking pos’n.
I could run a separate feed from the battery but that seems to miss the point of the ign key.

I’ve just checked the switch positions on the wiring diagrams and it suggests a 280z has a different function to the 240z yet on Z store they are the same part. Anyone got a 280z switch I could borrow / buy?

 

[Turn & Burn]

 

[jonbills]

I can't remember for sure, but I think I took a feed from the coil resistor thingy that has power on ign and start positions.

 

[peter_s]

I took my power straight from the battery via a fuse

 

[Turn & Burn]

I took my power straight from the battery via a fuse”

I’ve taken main power direct from the battery, but the ecu needs a switched feed to power it up, if I take this direct from the battery the ecu will be permanently live.
The current switched feed drops out on cranking, you have a 280 tho, with I suspect a different ignition switch?

 

[Turn & Burn]

I can't remember for sure, but I think I took a feed from the coil resistor thingy that has power on ign and start positions.

I’ll try looking at this on the wiring diagram and see where it feeds from, not sure I’ve left the wire in place when I rebuilt the loom.

 

[jonbills]

Ballast resistor. That's what it's called!

 

[peter_s]

I’ve taken main power direct from the battery, but the ecu needs a switched feed to power it up, if I take this direct from the battery the ecu will be permanently live.
The current switched feed drops out on cranking, you have a 280 tho, with I suspect a different ignition switch?

Im sorry, i was wrong (having some sake in my blood here). I took the power via a painless relay and fuse box. It's basically a fuse board that powers up via a relay. Google painless fuse box. It will help your installation a lot.

 

[peter_s]

The painless is triggered via a relay from the ignition switch. When the relay turns on the whole board gets power

 

[peter_s]

The painless is connected straight to the battery via extra fuses, but that source is controlled by the relays previously mentioned. Theu come as a package on the painless box

 

[Alphabettispaghetti]

The painless is connected straight to the battery via extra fuses, but that source is controlled by the relays previously mentioned. Theu come as a package on the painless box

that’s what I use to do on kit cars

 

[peter_s]

that’s what I use to do on kit cars

I think it's the easiest way. A painless box or similar will save you a lot of headaches in the long run

 

[Turn & Burn]

Ballast resistor. That's what it's called!

I’ve had a look, the ballast resistor is bypassed during cranking by an extra feed direct from the ignition key at 12v, so you have max spark power, once u come back off the starter motor the ballast resistor is then back in play, fed from the normal feed which drops the coil volts to make things last longer.
So essentially 2 feeds, I’ll try taking a feed from that pin on the switch (coil feed) and commoning it up with the run position, there may be a momentary dip as the switch contacts change.
I’ve not got the old coil or ballast anymore so the coil feed wire is not needed for anything else.

 

[Turn & Burn]

I think it's the easiest way. A painless box or similar will save you a lot of headaches in the long run

I’ve built exactly the same but is doesn’t cure the lack of ign feed when the motor is cranking! You need a permanent ign controlled feed, and whilst the 280z has this the 240z doesn’t. It seems is a foible of old ign switches, ie Mk1 escort included, where the intention is to get max volts to the starter and coil.

 

[peter_s]

How is the ignition swith different on the 240z?

 

[Turn & Burn]

How is the ignition swith different on the 240z?

Check out the images in my 1st post above, it shows the 280z maintains live feeds to the main circuit during cranking

 

[jonbills]

I’ve had a look, the ballast resistor is bypassed during cranking by an extra feed direct from the ignition key at 12v, so you have max spark power, once u come back off the starter motor the ballast resistor is then back in play, fed from the normal feed which drops the coil volts to make things last longer.
So essentially 2 feeds, I’ll try taking a feed from that pin on the switch (coil feed) and commoning it up with the run position, there may be a momentary dip as the switch contacts change.
I’ve not got the old coil or ballast anymore so the coil feed wire is not needed for anything else.View attachment 41859

yeah thats what I've done basically.

 

[peter_s]

Check out the images in my 1st post above, it shows the 280z maintains live feeds to the main circuit during cranking

Thank you, I've learned something good today

 

[jonbills]

here's how mine is wired. two of the wires on the ballast resistor are the ign and start feeds, the third is the supply to the relay supplying the Speeduino.

 

[Turn & Burn]

here's how mine is wired. two of the wires on the ballast resistor are the ign and start feeds, the third is the supply to the relay supplying the Speeduino.
View attachment 41864

Thanks Jon, I successfully bridged them up at the ign switch this morning. Checking with a fluke (multimeter) it provided an uninterrupted 12v feed even as the key switch was turned from run to start pos’n.