Very unusual electrical issue

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LOL glad you got it, i asked about the engine ground in post #4 on page 1.

woohooo you are up and running.

 
I had the same problem on a 71 Mach 1 with a 302 all original motor but knocking, before I pulled it everything worked when I installed the new engine nothing would work and I did not remember pulling a ground strap off! It took several months of hair pulling and cussing finally called a friend he came over looked at it for a couple of minutes, Then asked if I had a pair of jumper cables? He hooked them up to body and block low and behold everything worked! UGH!!:huh::udaman:: was my response!

 
Ah now that would be frustrating! Nothing worse than a bad ground or lack of ground especially. I didn't pull a ground cable off either which is funny. How it worked before I have no idea. I just added a "special" ground strap to the radiator support.

 
Yeah! We bolted this one to one of the heater box studs then to back of the block. I just used a new battery ground cable with female ends on it.

Sent from my iPhone using Tapatalk

 
the first picture i tried to compare to my car.

i think you have that black wire with the green connector on the left side of the starter solenoid connected incorrectly.

here have a look







the second photo, you have the; oil sender, the carb idle up solenoid, the A/C compressor magnetic clutch connector, coil, and coolant temp sender.

if you ditched the stock carb then the idle up solenoid can be used as a electric choke connection. it is powered 12v switched when the key is set to start and run and shutdown when the ignition is off or ACC mode.

the original purpose was on A/C cars there was more drag and it required a very high idle however the cars would diesel after shutdown when hot, so ford made the idle up solenoid that bumped up idle high to compensate and then on shutdown the solenoid allowed the carb to completely drop idle rpms to prevent run on after shutdown. so the solenoid was on all the time except when the engine was shutdown, perfect for an electric choke.

if you have some 100% isopropyl alcohol put some on a rag and you can clean up the wires and connectors so you can read the colors easier.
72 H code I don't want to highjack the post. I was wonder where you got the bracket that goes from the battery hold down to the fender sidewall. Mine is missing and I need the bolt and the bracket.

Thanks John J
Didn't take the time to read all the posts, but when I changed my alternator harness I had a no start issue but had lights etc. I had to run a wire from the alt GRD post to one of the VR mounting bolts and that fixed the problem. Not sure if my installation is correct, but it got the car starting again. BTW.........it is a 302.......:-/

 
the first picture i tried to compare to my car.

i think you have that black wire with the green connector on the left side of the starter solenoid connected incorrectly.

here have a look







the second photo, you have the; oil sender, the carb idle up solenoid, the A/C compressor magnetic clutch connector, coil, and coolant temp sender.

if you ditched the stock carb then the idle up solenoid can be used as a electric choke connection. it is powered 12v switched when the key is set to start and run and shutdown when the ignition is off or ACC mode.

the original purpose was on A/C cars there was more drag and it required a very high idle however the cars would diesel after shutdown when hot, so ford made the idle up solenoid that bumped up idle high to compensate and then on shutdown the solenoid allowed the carb to completely drop idle rpms to prevent run on after shutdown. so the solenoid was on all the time except when the engine was shutdown, perfect for an electric choke.

if you have some 100% isopropyl alcohol put some on a rag and you can clean up the wires and connectors so you can read the colors easier.
72 H code I don't want to highjack the post. I was wonder where you got the bracket that goes from the battery hold down to the fender sidewall. Mine is missing and I need the bolt and the bracket.

Thanks John J
Didn't take the time to read all the posts, but when I changed my alternator harness I had a no start issue but had lights etc. I had to run a wire from the alt GRD post to one of the VR mounting bolts and that fixed the problem. Not sure if my installation is correct, but it got the car starting again. BTW.........it is a 302.......:-/
I skipped to the end because I figured it was a ground issue (had em myself) but you guys have figured it out already. The battery cable to the block just isn't sufficient. Probably because of the rubber isolaters on the engine, tranny mounts etc not allowing a ground to the body.

Grant

 
yup you need the ground strap.

the engine does not have a direct ground to the body. the motor and transmission mounts do not conduct. the ignition system is self contained and requires ground through the engine.

so without the strap you have a open circuit

 
Yeah! We bolted this one to one of the heater box studs then to back of the block. I just used a new battery ground cable with female ends on it.

Sent from my iPhone using Tapatalk
I also saw an alternator wiring schematic that showed a wire going from the "grd" stud on the alternator to the negative battery cable/post. I now have a wire (not 10ga. like the schematic calls for), running from the alt grd stud to one of the vr mount bolts. I am going to reroute and replace the wire run to go from the alt grd stud to the female pigtail on the negative battery cable. Does that sound feasible?

 
pics are from a couple years ago another member asked about wiring and i remembered i had photos. I rebuilt my entire front end back in 2007 try to keep the bay clean but its a driver :)

the junction block on the apron is a ground isolator, basically its a piece of plastic that bolts to the apron and has a bolt molded into it so you can hook up that black and orange stripe wire to it. from the alternator harness that large black wire with the large eyelet goes to the ground isolator junction block, then from the engine harness is a similar black wire and they go together on that junction block.. you can tie both wires together and then wrap it in electrical tape to prevent a short, quick way to try and see if it solves the problem you have also. I remember way back somebody had wired that black-orange stripe wire wrong on my car and i had no power to my dash at all.

the only thing is the green and red wire is your coil wire so you need that, everything else is sensors and A/C.

it won't hurt to hook up the sensors and see what is working on the dashboard gauges. be nice if you get a oil and coolant signal on the dash.

well all this may not solve the issue but lead you closer to finding the source of the problem.

I rebuilt my engine harness i had a lot of broken wires and broken connectors on my car you could still have a broken ground or a wire somewhere.

72HCode, +1 on the clean engine bay! Ok so I see I'm missing that black connection piece attached to the apron next to the starter solenoid. Is that a ground? Also I do see you don't have the wire going to the left side of the solenoid that I have. I'll take that off. That is from the alternator so I think that one goes to the black connection piece on the apron which I'm assuming is a ground.

Also, thanks for describing that last picture picture. Theoretically, the engine should still fire and I should still get power to all accessories if that whole harness is unplugged because that's just the engine sensors correct? If so I can worry about that last.

I do have the stock carb from a 71 Thunderbird (where the motor came from) so I'll use that carb solenoid as such and I'll also splice into it for my HEI distributor.

Thanks again 72H!
Just being nosy and surfing the site......is that ground insolator necessary? I don't have one, and I don't seem to have any electrical issues. I am always looking for ways to correct the PO's handy work.

 
Couple options for bracket.

http://ohiomustang.com/store/order_page.asp?itemid=2931

http://www.mustangsunlimited.com/itemdy00.asp?T1=1705R+01

the junction block looks like its hard to find now years ago you could get them NOS from various mustang websites and on ebay.

72 H code I don't want to highjack the post. I was wonder where you got the bracket that goes from the battery hold down to the fender sidewall. Mine is missing and I need the bolt and the bracket.

Thanks John J
 
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