Electrical problem

[89-5leet-eh]

When i initially start the car(1989 Mustang 5.0l LX) it fires up fine runs fine etc, i shut it off and then try to start it up again( after a 10-20 min drive).I get a slow crank over and the small wire on the negative side( at battery terminal to inner fender ground) gets very hot -begins to smoke and car wont start.Most of the time the fuse for the instrument cluster(15 amp) blows and i lose all response/power for instrument cluster guages.I had the dash apart to change the heater core it was after that the problem started.I noticed the pigtails going into the back of the plug for the headlight switch slip out.I have pushed them back in and tightly wrapped tape around the wires to hold them in place.After the car sits for a while 5-10 mins it will fire back up again just fine and if i turn it off same thing again it wont start -wire smokes.Is this a ground problem with that smaller wire off neg terminal, is it the headlight switch/plug, a pinched wire behind the dash related to the instrument cluster or possibly something else.
The heavy main battery ground is bolted to the bottom right side of the engine block and seems to be properly secured.

 

[jrichker]

You have a bad engine block ground.
The fact that the small ground wire begins to smoke is the giveaway clue.
Remove the battery ground where it bolts to the block. Inspect the cable for corrosion, and damage. Clean the cable lug with not flammabe brake parks cleaner. Then clean the block with the same stuff. Sand the cable lug and block with fine sandpaper and reassemble everyting

1.) The main power ground is from engine block to battery: it is
the power ground for the starter & alternator.

2.) The secondary power ground is between the back of the
intake manifold and the driver's side firewall. It is often missing or
loose. It supplies ground for the alternator, A/C compressor
clutch and other electrical accessories such as the gauges.
Any car that has a 3G or high output current alternator needs
a 4 gauge ground wire running from the block to the chassis
ground where the battery pigtail ground connects.
The 3G has a 130 amp capacity, so you wire the power side
with 4 gauge wire. It stands to reason that the ground side
handles just a much current, so it needs to be 4 gauge too.

The picture shows the common ground point for the battery & extra 3G
alternator ground wire as described above in paragraph 2. A screwdriver
points to the bolt that is the common ground point.
The battery common ground is a 10 gauge pigtail with the computer ground
attached to it.

Picture courtesy timewarped1972

Correct negative battery ground cable.

Here's how to use a voltmeter or DVM to troubleshoot bad connections.
See Automotive Test Tools for help for help troubleshooting voltage drops across connections and components. .

 

[89-5leet-eh]

NT

Thanks alot for the reply, ill dbl check that block ground and sand a shiny spot to tighten up to.I had the engine and trans out to clean it up and repaint the engine and engine compartment so a layer of paint and maybe loose bolts is causing it, i remember the ground at back of intake to firewall and will dbl check as well as inner fender near battery, will make sure they're against shiny metal.Got an oil leak to fix at back of tranny, new seal didnt help so probly yoke, then a leaky PS pump to replace, then a leaky radiator -noisy pullys to replace, a conversion to delete the A/C pump. Hopefully by then my new exaust X pipe will stop smoking eheh.Then on to body work paint and an interior resto..../sigh
Thanks agn--- your wealth of knowledge is always appreciated and impressive.

 

[lincoln+ford]

Heres a lil tip if you ever think its a ground problem grab your jumper cables and use them as a temp ground cables to see if that helps easy and dosent cost you a dime.