Re: [DML] Electrical Troubles

["ksgrimsr" <knut.s.grimsrud@xxxx>]

--- In dmcnews@xxxxxxxxxxxxxxx, Louie Golden <louie@xxxx> wrote:
> ... It'll show 10.5 volts on the gague, and read almost 14 
straight from the battery.

If the voltage for the same rail is different at two different 
places, then you have a voltage drop from the one place to the other.

Voltage drops can be due to a number of factors including:
1) Current draw through the interconnect is high relative to the 
gauge of the wire carrying the current, resulting in a voltage drop 
(and some heating of the wire). For instance, when the fans kick in, 
there is substantial current being drawn and the measured voltage at 
the fans may be lower than the measured votage at the battery (or at 
the alternator) due to the IR voltage drop through the cable.
2) Interconnect suffers from resistive connections. This is often 
the case with our cars where some of the terminals have corroded and 
is especially a problem with ground connections. If you have a poor 
ground connection, then you get a voltage drop across the ground 
connection resulting in the effective voltage being seen as less. I 
believe the ground connection for the dash is on the driver's front 
frame (I think you can see it with the driver's front wheel 
removed). A lot of other high-current circuits also get their ground 
from the same point including the lights and the fans. If the ground 
connection is not good, then you'll get a voltage drop across the 
ground connection resulting in the effective measured voltage 
dropping correspondingly. There's also the main battery grounding 
terminal in the rear of the car to worry about as well.

If the voltage for the same rail is different in two places, then 
you should ask yourself why that's the case if they are electrically 
connected.

Knut