ground cable melting?

[jamrok55]

i have a 89 and there is a thick ground wire going from the battery to the motor by the oil filter then i have a smaller gauge ground going from the battery to a ground on the fender behind where the coil pack bolts up and for some reason my car cranks slow and the smaller gauge wire starts to melt and the car wont start i checked with a test light and i am getting a light from the positve terminal to both grounds so i dont get it someone olease help me

 

[FastFord58]

Whelp, a wire melting is a good sign of over-voltage or the wire just isn't thick enough to handle the power going through it. Is it a stock ground or is it an add-on because of a stereo or something?

 

[jrichker]

Grounds are important to any electrical system, and especially to
computers.

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 & alternator

Picture courtesy timewarped1972

3.) The computer has its own dedicated power ground that
comes off the ground pigtail on the battery ground wire. Due to
it's proximity to the battery, it may become corroded by acid
fumes from the battery. It is a black cylinder about 2 1/2" long
by 1" diameter with a black/lt green wire. You'll find it up next to
the starter solenoid where the wire goes into the wiring harness


4.) All the sensors have a common separate ground. This
includes the TPS, ACT, EGE, BAP, & VSS sensors.

5.) The O2 sensor heaters have their own ground (HEGO ground)
coming from the computer. This is different and separate from
the O2 sensor ground. It is an orange wire with a ring terminal
on it. It is located in the fuel injector wiring harness and comes out
under the throttle body. It gets connected to a manifold or bolt on
back of the cylinder head.

6.) The TFI module has 2 grounds: one for the foil shield around
the wires and another for the module itself. The TFI module
ground terminates inside the computer.

7.) The computer takes the shield ground for the TFI module and
runs it from pin 20 to the chassis near the computer.

8.) The computer's main power ground (the one that comes from
the battery ground wire) uses pins 40 & 60 for all the things it
controls internally.

See http://www.fluke.com/application_notes/automotive/circuit.asp?AGID=1&SID=103#volt
for help troubleshooting voltage drops across grounds

Extra grounds are like the reserve parachute for a sky diver.
If the main one fails, there is always your reserve.

The best plan is to have all the grounds meet at one central spot
and connect together there. That eliminates any voltage drops
from grounds connected at different places. A voltage drop
between the computer ground and the alternator power ground will effectively
reduce the voltage available to the computer by the amount of the drop.

 

[HISSIN50]

With the help of the two posts above, you should be able to get to the bottom of it. Chances are that the bigger ground cable leaving the battery became resistive or deficient, so the smaller wire was recruited to help out, and is now trying to do the task of the bigger cable. You might also find that things like the accelerator cable attempt to be used as a ground pathway (a new path of least resistance).

A single jumper cable can be nice for diagnostics. If you place it on the negative battery terminal and ground the other end on the engine, and if the engine now cranks over strong, you know you need a new negative battery cable. You can do the same test from the engine to the frame rails (shiny metal) to check the motor ground.

Once you get it figured out, ensure all the cables JRichker noted are up to par to avoid future issues.

Good luck.

 

[MT 408 Sparky]

Check the connections. I would guess that the large wire is not carrying the load so the small wire is. Replace and or clean all ground connections.

 

[tmoss]

Check the connections. I would guess that the large wire is not carrying the load so the small wire is. Replace and or clean all ground connections.

exactly - the large cable and/or connections are bad. My large cable bolt in the timing cover had the threads corroded internally (galvanic corrosion) making a VERY poor connection. I put a new calvbe on and moved the connection to the head.