I am doing a 93 4cyl conversion. I have the 93 V8 ecm harness plugged into the original 4cyl dash harness. I am wondering if I have to change the headlight harness. I thought I read that the headlight harness is different between 4cyl and 8cyl. However the dash harness is all the same. Anybody know for sure, and where I could find the v8 headlight harness if I need one?
1993 Mustang Headlight harness
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Nicoleb3x3
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I 90% beleive I had to change the headlight harness because the alternator was part of that harness and it's going to be located on the other side of the car 
Dash harness WORKS AS IS...however; IF YOUR FUEL PUMP DOESN'T TURN ON YOU MAY NEED TO DO WHAT I DID:
Originally Posted by MrKwik
quote from here: 302 swap problem - Mustang Forums at StangNet
For one, I wouldnt suggest using the 2.3 EFI pump. But as far as not coming on....did you remove the computer and EFI harness when you swappen in the 5.0? If you did, you would have to do some creative rewiring to get the fuel pump to run. The easy way is to just splice 2 wires together in the passenger kick panel where the computer used to be. I can tell you exactly which wires but it will have to wait till I get home this evening. I made wiring diagrams when I rewired my 4cyl to 5.0 cars. There is a green and a grey connector in the kick that have the wires you need. You just splice a "hot in run" wire to the fuel pump wire. I think the hot in run wire is grey/yellow and I'm thinking that the wire that goes back to the inertia switch is red/blue but dont hold me to that. I personally like to wire in a relay and oil pressure switch so that the pump doesnt run if the engine isnt running but it isnt totally required.
OK, I have the correct wire colors now. The "hot in run" wire is grey with a yellow stripe. The wire to the fuel pump inertia switch is dk green with a yellow stripe. They are both located in the passenger side kick panel by the ECM in the green 8-pin connector. I Always wire in a relay and an oil pressure switch but you can just solder and shring them together and the pump will run whenever the key is in the IGN posistion.
I know this is correct for 91-93 but you didnt say what year your car is so if its older I suppose there is a possibility the wire codes could be different.
Attached Thumbnails
I wasn't going to do the relay..I was just going to splice the two wires together...like this:
Dash harness WORKS AS IS...however; IF YOUR FUEL PUMP DOESN'T TURN ON YOU MAY NEED TO DO WHAT I DID:
Originally Posted by MrKwik
quote from here: 302 swap problem - Mustang Forums at StangNet
For one, I wouldnt suggest using the 2.3 EFI pump. But as far as not coming on....did you remove the computer and EFI harness when you swappen in the 5.0? If you did, you would have to do some creative rewiring to get the fuel pump to run. The easy way is to just splice 2 wires together in the passenger kick panel where the computer used to be. I can tell you exactly which wires but it will have to wait till I get home this evening. I made wiring diagrams when I rewired my 4cyl to 5.0 cars. There is a green and a grey connector in the kick that have the wires you need. You just splice a "hot in run" wire to the fuel pump wire. I think the hot in run wire is grey/yellow and I'm thinking that the wire that goes back to the inertia switch is red/blue but dont hold me to that. I personally like to wire in a relay and oil pressure switch so that the pump doesnt run if the engine isnt running but it isnt totally required.
OK, I have the correct wire colors now. The "hot in run" wire is grey with a yellow stripe. The wire to the fuel pump inertia switch is dk green with a yellow stripe. They are both located in the passenger side kick panel by the ECM in the green 8-pin connector. I Always wire in a relay and an oil pressure switch but you can just solder and shring them together and the pump will run whenever the key is in the IGN posistion.
I know this is correct for 91-93 but you didnt say what year your car is so if its older I suppose there is a possibility the wire codes could be different.
Attached Thumbnails
I wasn't going to do the relay..I was just going to splice the two wires together...like this:
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