[marcpuma]

Greetings fellow enthusiasts,

I've recently pulled my Mustang out of the shop with a new head and valves as well as some electrical work due to my battery not charging (which was not due to a faulty alternator, turns out my dash was continually pulling power). About a week ago my speedometer was registering a higher mph than I was driving and I could smell a wire-burning smell. I immediately drove home and was unable to find anything. A couple days passed and my Mustang was then dying due to an uncharged battery. Now it is stalling while idle. Can anyone advise? I do have an appointment with my mechanic tomorrow but I am looking for other advise. Thanks again!

 

[SDMustangRider]

Sounds like something I'm somewhat am or did go through. Been dealing with ground issues. I thought it was my headlight-alternator harness which it somewhat was the issue. Changed that and started my car 4x with no problems. The 5th time it was running, the car just cut out. Seemingly there's some type of bad ground going. Hopefully in some cases like I had last year, it's not any of your dash wires that are exposed and touching each other. So far so good but I think I might just suck it up with the money and get a new oem harness so I know all my wiring are new.

But I'd definitely lean towards a bad ground. Just start going through every possible grounds. Inside and out. I've been doing that for the last 2 weeks. My car's been looking like spaghetti. Hah

 

[franko66]

the speedometer should not have anything to do with how the car runs or probably did not smell like a wire burning. More than likely the speedometer cable is touching an exhaust pipe and melted the rubber jacket on cable and eventually lost lubricant and is causing the cable to operate radically. I would just search this site and you will find all of the helpful tips to trouble shoot the electrical system for shorts in the circuits.
a meter is all you need. Its called parasitic drain regarding a dead battery condition when not driving a short while.

 

[franko66]

go and buy a multimeter. Lowe's has a decent GreenLee digital for around 30 bucks that can check DC volts, Ohms, and amperage. Start out with getting the battery charged back up to full charge with a battery charger. reconnect the battery to the car and start the engine. Using the meter with setting adjusted to the 12VDC range place the red test probe lead on the positive terminal and place the black lead on the negative terminals on the battery. With the car running you should be reading 14 to 14.5 volts. If not then check for good connections in the wiring at the alternator. While the car is running and being CAREFUL have someone hold the test probes and read the voltage at the battery while you slightly pull and move the wiring around at the alternator harness and the voltage regulator wiring, etc. then see if the voltage readings change. This is how I located a short in my car. The short was located in the wiring that tunnels in the radiator core support. One wire was brittle and replaced.
problem solved. You mentioned you just got it back from a shop that also did some electrical work? what did they do? hopefully you can bring it back to them?
good luck.