[DeTomaso] Factory Shunt? was Re: Ammeter, was Re: Key difficult to turn

[David Fisher]

Guido,



I'm just finishing up on a similar adventure and this is what I ended up
doing. First up, my goals for the rewiring:

1 - have the alternator (Alt) charge the battery with A/C, lights and fans
on at idle (800 rpm)

2 - Not have a wiring fire from the new hipower Alt

3 - Re route window switches to center console.



I suggest you get your hands on SOBill's wiring diagrams (I think hosted at
Pantera Place) and look at page 11 and 12 for a while. Bill does a nice job
of explaining how the ammeter circuit works and has a simple schematic to
go along with it.

I ended up deciding that I wanted to keep the ammeter, but limit the
current flowing through it to 70 Amps. The wiring and the ammeter itself
seem up to the task so long the connections are clean and tight. (It's
oxidation on the connectors that creates resistance and hence heat).   The
Alt I chose can deliver 160A so I also wanted to ensure it could not cook
the wiring of the car under any possible load situation.



My solution was to have most of the heavy electrical consumers to be wired
directly to the alternator and not got through the ammeter circuit under
normal use.     I did this by inserting a 70A circuit breaker on the
ammeter circuit, between the ammeter and the Alt, cutting the stock line
from Alt back to the ammeter.   I took a 4AWG line and ran it from the Alt
through the passenger door tunnel and up onto one side of the circuit
breaker.   On this same lug,  I connected a 8 AWG line to the fan relays,
another 8 AWG line to the ignition switch and a 3rd line (stock wiring) to
the fuse box.   Thus, all the fuses get current off my heavy Alt line,  the
ignition switch gets a heavier wire directly from the Alt, and the cooling
fans gets a heavy line directly from the Alt.



The circuit breaker is shown below (this pic shows the Alt lug on the lower
right and was taken before my 3rd line described above was added.)



http://poca.com/index.php/gallery/?g2_itemId=38311



On the other side (top left) of the circuit breaker, I have the factory
black Ammeter wire going to through the Ammeter and then off to the
Battery.   The usual power line to the ignition has been removed and
replaced with one of the lines from the bottom right lug.



The circuit operates as follows.   When the breaker is closed, it’s the
same as stock wiring, except that if my Alt ever does put out anything like
100A, it travels from the engine to the fuse box on a 4AWG line and then
splits the current out on 3 8AWG lines to fans, fuse box (horn, wipers,
A/C, etc) and Ignition switch (the switched part of the fuse box, both
Accessory and Ignition).  If for some reason the battery itself draws more
than 70Amps (through the ammeter), then my circuit breaker flips, but the
car continues to run, powered off the Alt.  Conversely, if the Alt stops
working and for some reason the car consumes more than 75A from the battery
(unlikely), the circuit again flips off and (hopefully) no individual wire
has gotten hot.



 (Note there was recently a long thread about running an Alt without a
battery, but I ran the tests and feel confident that the 1 wire Alt I am
using can do it without problems).



This should protect from most all of the likely cases of meltdown in a
stock Pantera.    Note that the most likely case to cook your wiring is to
jump start someone else from your battery.  When you do this, especially
with a newer Alt, potentially all of the current your Alt is capable of
putting out will be running through the ammeter circuit over to your
battery and then off to the persons battery you are trying to jump.   Someone
on the forum noted this unfortunate situation happened to them.  With this
breaker, you can jump start someone, but if they draw more than 75Amps from
the Alt,  the breaker will flip and they will only be able to draw current
from your battery.



If I was to go the distance on this,  I would also run the headlight power
back to the lower right lug on my breaker as the headlight power is spliced
into the Black Ammeter wire somewhere between the fuse box and the steering
column.



notes:



1)      I wired my fans such that they will run even with the key off.   I’m
ok with this as my new Alt does a great job of charging and I don’t mind
the fans cooling down the rad when I run into a store.   You could wire the
fan relay from the ignition switch or fuse block if you wanted it to shut
off with the key.

2)      This was pretty easy to do once the dash was out.  Running the wire
down the passenger rocker panel can be done fairly easily with the
Passenger seatbelt removed.

3)      Recall that the heaviest electrical consumer (the starter) is
independent of all of this.  It has its own direct line from the Battery,
through a starter solenoid to the starter



Good luck,



David