Wiring Harness issues

[steve-0]

I've purchased a Ron Francis EFI harness for my '75 with a trick flow intake, MSD ignition, and an American Autowire "early bronco update" harness fromn Wild Horses. I've got it all hooked up, but I'm not getting spark. I think the issue is with a couple of connections. Namely, the Ron Francis harness has a three prong plug that contains an "ignition run" along with a temp sensor lead and an oil pressure sensor lead that powers all the relays and sensors in the harness on the drivers side, and the AA harness has an ignition feed on the passenger side that's intended to go to the positive side of the coil. The AA ignition feed is pink and has power. I was told by Ron Francis to splice these two together and use the power for the coil on the Ron Francis harness to connect to the coil. I've done it, and the engine harness does have power at the red wire on the coil...but I still get no spark. Anybody got any clues? Advise?

 

[DirtDonk]

Hmm, interesting. Sorry to hear you're having this frustrating issue at this final get-it-running stage!

Seems you have power now, but pretty sure you're not supposed to have power at the coil. The coil gets it's signal to spark, and it's keyed power through the computer I thought? Or maybe I'm wrong and it's just the spark signal that the computer sends? Sorry, been awhile since I had to track down a no-spark issue with one of these EFI setups and I'm forgetting some key stuff.
Hopefully others will remember.

Are you getting constant power to the relays?
Do you seem to be getting power to everything else? And the AAW is a Pink wire you're using for power? What does it say on it? Is it possible that Pink is a START-ONLY circuit and not full power when the key is ON?

What about START power? Are you getting s START signal to the computer?
And the TFI module? Is that new, or used from the old engine?

Also, make sure it's an ON wire, and not an ACC wire or you will be running everything just to listen to the radio.

I'll go check my AAW diagrams, but that may take a bit. If you have them handy what does it say about that wire?

Thanks. Good luck!

Paul

 

[steve-0]

So, after half a dozen calls to MSD, Ron Francis, and American Autowire I'm closer, but still at an impasse. I've connected the engine harness to the accessory fuel pump power on the body harness and the pink ignition feed to the MSD power connection along with the hot coil connection from the engine harness and once cranked the MSD box maintains power even though the key is switched back to off. Still no spark when cranking. I'm wondering if it's the ECU not relaying the pulse signals to the coil.

 

[DirtDonk]

Got a picture of your engine compartment? What distributor are you running, and what coil?
Are you running just an MSD distributor, or are you talking about an external control module such as a 6-AL or similar?

Have you had to modify any wiring to get it to fit with your components? Or do things just plug in, such as the connector on the RF harness to a standard E-core type coil?

What kind of testing have you done to the distributor trigger mechanism? Verified that the distributor is turning with the engine? Just wondering if a pin has sheared or a gear has been compromised.

It's very rare for one of these harnesses to have defective connections from the factory, but it's not impossible either. You may need to track down a fire signal.
And you said you had a TrickFlow intake, but what EFI system are you running? What computer specifically, and which TFI distributor?

Thanks. Good luck.

Paul

 

[steve-0]

Thanks for the shot in the dark. I realize this was a wide open topic. I appreciate your input. I did, however, manage to figure it out. The TFI sensor on the distributor was bad. Only took about a month of Sundays to track it down.

 

[DirtDonk]

Congrats on the find. Was it a new one, or a used one from a donor engine?

Paul

 

[steve-0]

continued issues

Well...in the process of hooking up the rest of the parts I've amassed since firing the engine...I'm running into an issue with the TFI sensor. I'm getting power ~4.9V across all three wires. Doing the research says I've got a ground issue somewhere. I'm assuming I've got the AAW ignition feed connected incorrectly.

I'm running an MSD 8456 distributor and an MSD 6A digital ignition box with a blaster coil.

I'm not sure where to connect the 12V ignition feed from the American Autowire harness. Currently, I have it connected to the body harness attachment on the Ron Francis engine harness. The engine harness comes with coil connections and I have those wired to the MSD 6A.

It's my suspicion that the ECM is bad, but I've taken it apart and noticed no visible short on the sensor ground.

Another shot in the dark to see if anyone has had this issue before? You think I should pull the AAW ignition feed straight to the red wire on the MSD 6A?

 

[DirtDonk]

Well if you are running a TFI distributor then I would think that literally nothing in the chassis wiring should be connected to the ignition at all. At least not to the distributor or coil. That should all be integral with the RF EFI engine harness.
How is the MSD 6a spliced into that setup?

Do you have an instruction sheet that shows how to integrate the MSD 6 into a Ford EEC-IV computer controlled ignition system? The 6a box is the only thing that would change how stuff is working, because the normal method of connecting the TFI module and ignition coil is to use the dedicated wires coming from the ECU.

If you have a link to the instructions for using the 6a with a TFI, post it up so we can check it out.
And verify that the distributor body has a good ground connection to the engine block.

Paul

 

[Otis Campbell]

I had a bad ECU one time in a mustang. Try to start it with the SPOUT removed. If it starts that's an indication that the ECU is bad.