JayEstes

I'd help.   It's been great, but sometimes people get too much to deal with.  I don't know much about it but am willing to help

I had an Optima yellow top last for 10 years, it was on a trickle charger when the car was in the garage.

Wow! The best until today I'd heard of was my neighbor who got 12 years out of his OE on his Toyota pickup.
 

Actually my 2014 Challenger got 8 years on its factory battery ,but it croaked just a few months after i bought the car ,it survived the previous owner 

Magnum 500 wheels need to be lug-centric balanced, nut hub centered.  Very few tire places have that capability.
Bad u-joint, incorrect driveshaft to tranny/rear end angles can also cause vibrations.

Bots are hitting the site and causing the issues.  I am working with tech support still to try and fix it.  I thought it was already resolved.  There is another issue with upgrading the forum software I need to take care of but it currently crashes the entire forum so I am unwilling to do so until I have ample time to devote to it.  I am hoping to have the bot issue resolved by the end of the week.
Just a little update for you guys.  Bandwidth upgrade would only be a bandaid and not a full solution, so do not feel obligated to donate any more money.  And thanks for your donations so far that should cover the monthly losses for the remainder of the year.

Well, sure enough, I had my harness routed improperly.  I never knew about that routing hole in the left side pocket- but it’s in the exact right place.  So I fixed it thanks to everyone. And No, that reverse light harness is never near either exhaust line line I mentioned.
Per the dual exhaust- I never knew there was a transverse muffler option.  I pulled the original crappy exhaust manifolds and single line I had and put cast iron headers with 2 separate 2.25 exhaust lines on each side with h-pipe.
thanks Mike for asking the question- I’m getting more out of this than I put in!
Jay 
 

Sorry about that, my son still hasn't gotten around to looking at that. For some reason he puts his work before mine- the nerve of him!
Here is a shot of the wire routing using the snipping tool. I show the Cougar version first because it is the only page that has the fuel sender wire that Mid mentions in the post above:
Cougar 2-E14 interior lights, clock, cigar lighter, but shows fuel sender wire

Mustang 2-E22 exterior lights, clock, cigar lighter. No fuel sender wire shown

I was worried that the wire could get chafed and start a fire as it does not have a grommet for the hole you used on trunk floor.

Jay, is that the reverse light wire going through the hole above frame rail on this picture? There should not be any wires going through that hole, reverse light wires goes out through holes towards the back bottom of trunk drop off.

From up over the left wheel:
left tail light:


 
gas gauge routing:

 
note I have spliced in a gas gauge calibration device here.  It’s in the 3d printed box I made for it there. It’s held down by one of the tank bolts. The wood is there to kind of even up the floor for the vinyl

 
this is the running of the tail light harness from the left side headed over to the right side.

Hope these help some!!
 

If the clip is in correct it locks into the molding  ,the spring is a preload to keep the clip in place while tightening ,i sometimes bend the spring to keep it a bit tighter if the clip feels to loose in the molding ,now when tightening the clip is turning into the channel at top and bottom and shouldnt be able to come out 

Damn, that's the first correct answer out of the last 8,439 responses!  I'm slipping, I tell ya...

Try unbolting the master cylinder & pull it forward a little & make the back seal in the master cylinder is not leaking fluid into the brake booster. I have had this happen to me & it drove me nuts until I found it.

Are your rear drums adjusted?  If there's a lot of space between the pads and drum, your brake pedal will feel much as you described.
The brake fluid must be going somewhere without affecting the braking ability.

Thanks ridge. I ended up installing without painting it. It was shiny aluminum after stripping the paint but I think the anodizing stayed on. 

Mine was cracked and it wasn't all obvious it was until I tried to pull it out of the booster, and it broke.  Make sure you get the right size hoses to go with it.  It should go from the booster into the main vac port on the back/top of the engine.  This hose is very important to overall vacuum, as it is a larger size, and leaks have a big effect.  It won't cost you but a little more to get the hose replaced.

The first thing I would check is the check valve where the rubber hose connects to booster. Also I had a vacuum booster once that leaked around the push rod shaft (the one between the booster and M/C} that caused the booster to function erratically sometime it sealed off and other times when you pushed the petal and released it wouldn't .

1 1/8in sway bar upgrade on the front is absolutely the best handling/safety upgrade I have made tot he car.  very little body roll for normal driving, much better handling

your sensor of the fan activity should be located at the exit of the radiator/entrance to the engine (lower hose).  basically, if the radiator (without fans) is able to adequately cool the fluid before it enters the engine, then there is no point in turning on the fans or have them turned up.    locating that sensor in the intake manifold will basically have you running the fans more necessary.  which of course won't hurt beyond consuming a little more energy/power at certain times.

65 66 is to narrow ,i have found the 1 1/8 front bar to be the best ,start going bigger and it can rip the sway  bar mount from the body 

A lot of people, present company included, based their less than stellar car's performance on worn out parts. Mach1 Driver is correct.  With proper functioning stock components, your brakes should do a good job. Anytime you change from stock, you're opening a can of worms that will bring in a few extra parts that will need modded. 
A guy in the Mustang world who really knows stock brakes, and steering, is Dan @ Chockostang.com.  He can be believed and trusted. 
 

This will be an unpopular opinion- they raced these cars with front discs and rear drums, and the stock brakes were good enough for that. Friction materials have improved in the 50+ years. For the street, barnett468 recommends EBC green pads and shoes, Zray uses EBC Redstuff 3000 Series Sport Brake Pads, and says that the popular Porterfield pads are inconsistent from batch to batch.
The advantage of going stock is that you don't have to guess how to set it up as its all in the Ford shop manual, the parts are readily available and the part numbers are known. Why reinvent the wheel when something works? Yes you can get aftermarket brakes with gigantic pistons and air cooled slotted rotors, but chances are you're going to be messing around with the system to get it right, and you won't be driving it. In my opinion, unless you're married to Shirley Muldowney, the stock brakes will be fine. Just my 2 cents.
 

Check the plug on the back of the ignition switch. It is common to have a burnt up connector on the plug on cars with a/c due to the higher current load. Back in the day when you bought a new Motorcraft / Ford ignition switch it came with a new pigtail to make a proper repair.

Remind us, is yours a 69 or 70? Fusible links started on the 70s, but the only one I'm aware of is at the solenoid, and would cut the main power. Once it is gone, power wouldn't be restored without replacing the link. This sounds like a loose connection somewhere.