Need 1973 Mustang schematic

Cudajim · Sep 28, 2025

I'm new to this Mustang blog being a Mopar guy and all but lately I'm into fixing Fords for customers and friends. I came across a '73 Mustang that has a current draw of 1 amp with everything off and my ammeter in series with the battery terminal. I need to find it so a free schematic would help, hopefully in .pdf format so I can yellow-line it as needed after I print it out. The owner also wants me to change out the instrument panel for a nicer one he already has. Any help would be appreciated. Thanks in advance. Jim

Mcmahst · Sep 28, 2025

Ask and you shall receive.

Cudajim · Sep 28, 2025

OMG, thanks so much... you made my day!!!

Noobz347 · Sep 28, 2025

Mcmahst said:
Ask and you shall receive.

You should create and upload this as a [Resource].

Cudajim · Sep 29, 2025

Mcmahst said:
Ask and you shall receive.

Cudajim · Sep 29, 2025

I printed the schematics on 8.5 x 11 paper, trimmed and taped pages 2 through 8 together for one long schematic. It's much easier to follow rather than flipping pages. It's the weirdest format I have ever seen for a schematic drawing but it works.

Mcmahst · Sep 29, 2025

It’s old school Ford. Just for info, and this is a great Mustang site, there’s a forum called 7173mustangs.com; focus us on 71-73 Stangs. Good luck.

Mcmahst · Sep 29, 2025

Resource uploaded waiting for approval.

Samplebridge · Sep 29, 2025

I would check the alternator. Unplug it completely and see if draw disappears. Had the bridge rectifier go bad once and it would draw enough to kill a battery overnight.

Cudajim · Sep 29, 2025

Samplebridge said:
I would check the alternator. Unplug it completely and see if draw disappears. Had the bridge rectifier go bad once and it would draw enough to kill a battery overnight.

That is one of the first things I suspect. If there's a bad diode in the alternator it will pull current. I saw it in a newer VW once. Other things I suspect are the aftermarket radio and aftermarket alarm.

Mcmahst · Sep 30, 2025

And the voltage regulator, should have a blue cover, is also a common source for drain. It’s easy to pull the connector off to test that. And, the new or replacement ones are now solid state. Good luck.

Cudajim · Sep 30, 2025

Mcmahst said:
And the voltage regulator, should have a blue cover, is also a common source for drain. It’s easy to pull the connector off to test that. And, the new or replacement ones are now solid state. Good luck.

We have to wait for better weather now so I won't get to it till next week. I'll report back especially if I find the problem.

Mcmahst · Sep 30, 2025

If we didn’t already mention it, we think MOPAR guys are ok, but just ok.

Cudajim · Oct 8, 2025

I just got a chance to look at this Mustang. I pulled out the dash gauges, aftermarket radio, alarm system, center console etc. It still draws 450 ma with everything off. There is no trunk light, hood light or glove box light to deal with. I pulled all fuses too.... still get a current draw. I also disconnected the one-wire alternator, there is no external regulator. Coming off the battery side of the starter solenoid is a white wire with black stripe which is where the current is going. Cannot find it on the schematic I have but I suspect it may be a problem with a stuck relay, seat belt interlock or something else that does not go through the fuse box. Problem is I cannot locate any relays on the car anywhere. Anybody out there know where to look?

Mcmahst · Oct 8, 2025

Ok, dumb question first. I assume you’ve taped the door courtesy switches do the interior light is not on. I had to post that, sorry,

Now, sounds like you might have an aftermarket under hood wiring harness. Post some pics of it if you can. I’d still post this over at 7173mustsngs.com only because there maybe someone there who will recognizes the pics and issue. Good luck

Cudajim · Oct 9, 2025

Mcmahst said:
Ok, dumb question first. I assume you’ve taped the door courtesy switches do the interior light is not on. I had to post that, sorry,

Now, sounds like you might have an aftermarket under hood wiring harness. Post some pics of it if you can. I’d still post this over at 7173mustsngs.com only because there maybe someone there who will recognizes the pics and issue. Good luck

I took the bulb out (temporarily) for the door switch so it's not in the circuit.

Cudajim · Oct 9, 2025

Ok success, I found the problem! Turns out the aftermarket Edlebrock 4bbl carburetor has an electric choke. Whoever the hack was that installed it decided to tap into power for the choke using the wiring under the hood. Unfortunately they picked a wire that's live all the time and also not protected with a fuse or even a fusible link. This caused the choke to be always open and of course to draw 450 ma of current all the time. Since it never choked it was also hard to start the engine. I rewired it properly so now the engine starts easily and no more dead battery. I also had to fix the convertible top switch. The owner bought a new one from Ford. The old one was a Radio Shack SPDT switch which was wrapped around the terminals and taped. It was a good look, probably done by the same wiring hack.

Mcmahst · Oct 9, 2025

Most folks use the carb solenoid wiring for the anftermarket electric choke, since it’s only on when the ignition is in run. Glad you tracked it down.

manicmechanic007 · Oct 10, 2025

Bit of a Dodge fan myself
Still looking for the right Charger to buy someday with a 440 six pack
Fastest car I ever rode in was a 69 Super Bee with a 440
My 427 Camaro will be no slouch
I might be selling my 69 Boss 302 Mustang soon to afford another hotrod

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