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I'm doing a MAF conversion on 86 f150 with the 5.0. Being I had everything tore apart and the existing harness was not in that great of condition I purchased Ford Racing's EFI engine harness part #m-12071-a50. Wiring to the engine components has been fairly start forward but I'm running into a lack of understanding on the additional wires to connect and looking for some help.
1). Says to make a mandatory connection to the check engine light with two wires, one positive, the other negative. Being there is no existing check engine light just an emissions light, how can these be connected?
2) says to connect one wire to the + side of the fuel pump but if over 25 amps route though a relay. What does the factory pump draw amp wise? Also since the new wiring harness has its own inertia switch with the wiring layout different, I'm thinking I can just use an aftermarket relay, the new wire cuts on the relay, then run a solid battery source to the relay for the fuel pump. In other words, is there any reason to maintain the original factory relay? But also what tells the fuel pump to cut off if demand is not there?
3) the new harness has a wire that says to connect to dash control ac switch. Being there is no such thing what do I need to do? Truck does have ac.
4) lastly, and not a mandatory connection, but a lead to the tachometer. Being I have that own conversation done to the cluster previously I'm thinking just leave this one unconnected.
3103 that you need to go the pages 60 & 63, here: Electronic Engine Control - ???Gary's Garagemahal. But none of that tells how much current the pump pulls. I can't answer that as mine is a carb'd 460, but it doesn't pull all that much. I was surprised that an 1156 test light actually ran my pump, although only for a few psi.
The AC connection is so the idle will compensate when the compressor comes on. So, disregard.
3103 that you need to go the pages 60 & 63, here: Electronic Engine Control - ???Gary's Garagemahal. But none of that tells how much current the pump pulls. I can't answer that as mine is a carb'd 460, but it doesn't pull all that much. I was surprised that an 1156 test light actually ran my pump, although only for a few psi.
The AC connection is so the idle will compensate when the compressor comes on. So, disregard.
The negative side of the coil serves the tach.
Gary, I have used your website already as a valuable information piece and had already printed the diagrams referenced.
1) In the case of the emissions light, what is controlled by? I suppose the best way to tap is is behind the plug at the cluster?
2) I've followed the fuel pump wiring diagram but the wiring of the existing and the new harness are not the same. In the existing wiring, does the fuel pump run all the time? If it does anyway, would I be correct by adding a regular relay to trigger it without worry of it running all the time? But if the engine is not running, but key is on, what trips it off?
3) I do have ac on the truck. The instructions for this wire indicates that it activates the ac clutch. If it actually only receives information, I'm thinking tap it into one of the wires already on the ac that becomes hot when the clutch is powered.
On the fuel pump wiring, go look at the wiring for the 7.5L, which is what I've been working on in Big Blue. It has an oil pressure switch that is in the coil circuit of the fuel pump relay. I'd add one of those to ensure that the pump only runs when the engine is running. And, don't miss the part where the fuel pump comes on during cranking.
On the AC, I really don't know what to tell you. But, I thought it was just to tell the computer that the compressor is on rather than to control the compressor. Perhaps you can get everything else going and then test that?
As for the emissions light, I wish I knew what controls it. Here's the one on Big Blue:
When the key is first turned on, the computer primes the pump and then it stops. When it see's signals from the distributor then it assumes the engine is turning and it turns the pump back on, using the relay on page 103 in this link.
I think I have a plan for everything just have to do some testing along the way. On another matter, can you tell me how to remove the terminal slots from the fuse block without tearing it all to pieces? Part of my current block is broke but I have a good spare if I can change the wires out.
If they are like most auto electrical connections you need a tool to push in the tab to release the fitting. https://www.summitracing.com/parts/sum-900402
The tool pushes in the tab and you pull the part out.
If you have a box in hand it should be easy to see the tab to release it.
Dave ----
When the key is first turned on, the computer primes the pump and then it stops. When it see's signals from the distributor then it assumes the engine is turning and it turns the pump back on, using the relay on page 103 in this link.
Factory wiring has two wires to the relay that connect to the eec. Of these the red is hot as is a yellow to to the relay. Why would there be two hot wires to the relay?
Yellow is from the battery feeding the the relay power. It also feeds one side of the coil in the relay. The computer grounds the other side of the coil on the tan/lightgreen (page 62 in the diagram link). This makes the relay "click" and it then sends power out on the red. The red is only powered when the computer selects the relay.
The way those diagrams are split up with the "yy" makes it hard to figure out.
Sorry, I was a little mixed up in my post. The EEC relay is the main relay, it gets power from the battery and when the keyswitch is turned on, it powers the red wire. The red wire goes all over the place, you can see that on page 60 here.
But the red having power on it does nothing for the fuel pump relay, because the coil is not grounded, the computer selects when to ground the fuel pump relay coil through the tan/lightgreen which leaves on the "yy" and goes to page 62 here (this is terrible isn't it?)
You can see on page 62, the tan/lightgreen goes to the computer, and it also goes out to the test port plug so you can ground that wire manually to test the fuel pump system. I would think the Ford wiring harness you have would have the test port plugs, you need to get to know these well so you can pull the codes and do other things also.
You are correct, power for the fuel pump comes from the yellow wire, goes through the relay, and goes out on a pink/black. It then goes through connector and changes to yellow. But these are early diagrams, this is the first or second year they came out with multi-port injection, and they start changing things right way. So your motorsport harness may do things a little differently, with basically the same results.
I appreciate the help. I believe I've got all the extra wires figured out and properly connected but now I've lost power on the starter relay circuit from the switch so I've got to trace that down. Then hopefully I'll be ready to move to starting the truck.
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