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Re: 99 Electrical Issues
Posted by Stottler - http://saabnet.com/tsn/forms/e.php3?em= (more from Stottler - http://saabnet.com/tsn/forms/e.php3?em=) on Mon, 1 Sep 2003 11:50:17
In Reply to: , Kok Chen, Sat, 17 Dec 1988 12:00:00 

This reply is a bit late as I am (as usual) going through last monthÕ
digestsÉ

The 99 electrical problems that John Zimmerman reported sound very much like
classic symptoms of one or more Òad groundsÓ  How do good grounds go bad?
Assume that the alternator merely charges the battery and that for each
circuit, the current must flow from the battery (positive terminal), through
the fuse for that circuit, through the appropriate switch or relay, through
the device, and then back to the battery.  This last bit (back to the
battery) is often tricky, as at this point the circuit may joint together
with other circuits and be attached to the body or the engine which is then
hooked back to the battery (negative terminal) with another wire or Òround
strapÓ  The electrical engineers out there may point out that the current
actually flows from negative to positive, but that makes no difference in
considering and troubleshooting this type of problem.   What tends to happen
is that the point where the offending circuit(s) attach to the body or engine
becomes corroded, forcing the current to try to find another path back to the
battery.  Thus you get weird stuff like John describes as the current from
one circuit, with nowhere else to go, disrupts other things tied to the same
ground.  Often a device that works with little current (like a fuel or temp
gauge) will work OK until something that takes high current (like a turn
signal) tries to use the same ground and finds that the resistance is too
high for the added current to flow to ground.  This would cause some of the
symptoms John is mentioning.

So how to fix this?  As usual, I tend to favor the Òtart at the very
beginning and fix all the fundamentals in orderÓapproach.  It is possible
that you could find one simple fix for all this such as a loose nut at a
single ground point, but if you methodically go through the entire system and
clean up all the grounds you will have a system thatÕ reliable in the long
run, and you will have also a much better understanding of your system.
Begin with the proper electrical wiring diagram for your car (in the service
manual, or I have seen them for sale on ebay lately) and locate the ground
points.  Any electrician or mechanic should be able to show you what they
look like on the diagram if youÕe not familiar with wiring diagrams.    Back
at the car, you must physically locate these ground points, which can be a
little more difficult Ðit just requires some digging (under/behind the
dashboard, for example, in the case of some of the symptoms John describes).
They will usually look like one or more black wires held to a stud on the
metal body with a nut and washer(s).

At each ground, remove the nut and washer, and clean up (you want to see
bright shiny steel Ðno paint or rust) the area of the body where the
terminal(s) (usually a ring terminal) contact the metal.  The body, the
terminals, the stud, the washers, and the nut should all be shiny.  Use a
wire brush and/or sandpaper for this cleaning.  When putting all back
together, I usually coat everything with dielectric grease (Radio Shack) to
prevent future corrosion.  Tighten the nut securely (donÕ overdo it ÐyouÕl
be really POÕ if you break the stud).

There are a few other places that might cause similar trouble with high
resistance connections Ðcorrosion tends to be an issue in any 25 year old
car, especially one that has spent any time in storage.   The wiring harness
connects to the back of the instrument cluster with a big, multi-pin socket Ðthis can be loose
or corroded.  Likewise, check the connection to the turn

signal switch.  Under the hood, the negative battery cable attaches to both
the body and the engine (bolted connections), and both of these points must
be clean and tight.  The alternator also grounds to the engine via its
mounting brackets, so make sure these are tight.    The fuse block in the 99
is at high risk of corrosion, both between the fuses and the sockets (remove
the fuses, clean the sockets with a pencil eraser, and bend the spring tabs
inward to increase the tension on the fuse), and between the terminals on the
bottom of the fuse block and the wires leading to them.

Of course there are other electrical issues that can cause the failure of a
single circuit, but when multiple circuits start acting up/interacting,
usually a ground problem is the culprit!  Hope this helps.

Gary Stottler

'78 99 Turbo
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