ECM wiring questions

[ratio411]

I am converting an 81 carb'd to 88 5.0 EFI.

I have the schematics, but I am not clear on the abbreviations and such.

The ECM has 3 hot wires according to the papers.

2 red hot wires, marked as "VPWR", and one black/orange wire marked as "KAPWR".

Now, one would think that "KAPWR" stands for "key activated power", but the schematic shows that one going to the battery. ???

The 2 red wires that are marked "VPWR" go everywhere, so it looks to me like those 2 are 'key power'. ??? The bad part is that the 2 red wires don't show a clear destination in the chart.

So my biggest question is:
Am I correct in sending the black/orange wire to the battery (full time hot), regardless of the "KAPWR" label?

Am I correct in running the 2 red wires to 'switched power'? Or do they go to constant power also???

Next...
The ECM grounds to the body, has a ground strap on the case, but also has a black/green wire that is marked as ground, but goes in through the pins. Do I just ground those wires, or are they in need of a special grounding? Also have a ground that is orange.

I just don't want to ground out something straight to the body and find out that it needed to be grounded to the lower voltage that the ECM sends out. Probably stupid worry, but I just don't want to slip up wiring this thing and fry the ECM.

Thanks!
Dave

OH...
There is a heavy gauge yellow wire coming down the harness that is nowhere on the schematics. ??? It is 3x as heavy gauge as the other wires, solid yellow, and I can't figure where it goes. Is anyone familiar with this wire.

FWIW, the 5.0 is a speed density HO out of an 88 Lincoln LSC. The ECM is supposed to be identical to a Mustang except for ECM controlled cruise control. The problem is the wiring harness is UBER COMPLEX compared to a Stang EFI.

 

[ratio411]

One more mystery wire...

There is a red/blue wire that goes between the ECM and distributor, then branches out of the harness.
The schematic says "start sol".
I know that means starter solenoid... but do they want that wire on the cable, which would make it 'constant hot', or do they want it on the solenoid activation post?

I can't see it being constant hot...
Am I correct in thinking that this wire is an ignition retard that only works when the engine is starting?
Therefore it would attach to the wire that activates the starter, only functioning until the engine starts.
Funny thing, that wire, from the key to the starter on the 81's wiring harness, is red/blue also. Coincidence? Or is that my clue?

 

[liljoe07]

VPWR is switched 12v. Usually comes from the ECM relay. KAMPWR is a constant 12v source.

Case ground is PIN 20 goes to a body ground. PIN 40 and 60(black with green stripe) just goes to another body ground or battery negative.

The red/blue wire goes to the start engage wire(starter activation) on the starter relay. That wire goes to the TFI. TFI has a start voltage circuit that only has power when cranking to retard timing.I might be wrong on that wire color as there is a red/blue wire that goes to the TFI also. They are right beside each other on the TFI connector. Ill check, but I believe the #3 wire on the TFI should have power only in crank mode, and the #4 wire on the TFI will have a constant 12v with the key on or in crank mode Yellow wire sounds like it goes to the A/C WOT relay.

 

[ratio411]

Thanks! Good info!

 

[ratio411]

Sounds like I need to put battery power on the 'switched side' of the ECM relay, and then send key power to activate the relay. ??? That way the ECM has full power from the battery, but only when the key is switched on.

 

[ratio411]

I have the collision fuel pump cut off from the trunk of the Lincoln.
Am I being too anal by installing it?
It will take some extra doing. Is it worth it or just overkill?

 

[liljoe07]

You need to wire the ECM relay so when it engages, it sends power to VPWR. VPWR should only be hot with key on. Inertia switch is your preference.

How do you plan on wiring the fuel pump up? I'm not familiar with the carb setup of the 81. I'd think its a mechanical pump setup???

You swapping tanks also?

 

[ratio411]

No tank swap. Just cutting a hole in the top of the tank to accept in tank pump.
I'll make a gasket and bolt down. Used most of the fuel lines off the Lincoln.
Have the harness for the pump. The relay was mounted in the trunk, so so wiring will be needed to move relay up front.

 

[liljoe07]

In stock form, VPWR is used to engage the fuel pump relay. So consider that, or run your own 12v switch for that.

To get the ECM to control the fuel pump, you need tie PIN 22 from the ECM to the negative side of the relay. This will operate the pumps initial prime. And start it back when a PIP signal is received from the distributor.