Re: Twitching gauges (was: 82 4000s no start condition - results)

[Eddi Jew <jew@rysa.dtc.hp.com>]

 >> My next question as I'm about to add a oil pressure gauge, is how 
 >> can I get 
 >> my gauges to stop twitching when my stereo hits a bass note?  Turning the 
 >> volume up has the effects of raising my oil temp. about ten degrees.  Go 
 >> figure.  And where is the best place to connect the volt meter to get the 
 >> most accurate reading?
 > 
 > Don't know about '82 4000's, but on the 84-88 5000 series there is a
 > voltage regulator in the dash whose output is used as a reference
 > voltage for all the gauges. Its output is something like 3.6 volts (don't
 > remember exactly though). This voltage regulator's output may be getting
 > affected by the stereo. How powerful is your stereo? If the current draw
 > is considerable, then it may be causing a significant voltage drop 

That's a good possibility.

 > that the alternator and its voltage regulator aren't able to keep up with.

Maybe. This depends on where the radio's power is tied at. If it's a 
powerful aftermarket stereo (or if you have a separate amp), and it's power 
is supplied by the same branch as the dash's (don't have the wiring diagram
here), and using the standard radio wiring harness, then the voltage drop 
might be limited to just that branch/circuit.

If this high-power radio uses thick wires connected to the battery or a 
dedicated supply off the fuse block (using a suitable fuse, of course), 
then the voltage drop in the wiring is not an issue, so do check the 
capability of the alternator/regulator. To check this:

         1. Measure voltage of +12V supply at the radio with full volume.
            Use a non-digital-display voltmeter to verify and 
            view the voltage and any swing (due to the bass kick) better.

         2. Measure voltage of battery. If around 12 - 13.5 (?) volts and 
            doesn't swing with the bass, then the problem is contained at
            the branch. Continue.

         3. Refer to a fuse block diagram/reference and find the dash 
            and radio supply. If both are on the same fuse and the same 
            voltage swing is seen, then replace the fuse (I'd seen rare 
            instances of fuses with a high resistance) and find another 
            unused or beefy fuse-block tap for the radio. Any amp over
            300 watts should have a direct connect to the battery, with
            the inline fuse located under the hood (before firewall).
            Moving the radio's power source may be faster than trouble-
            shooting all this because maybe nothing is "bad".

For buying info on high-current wiring and connectors, get a copy of a
car stereo mag (Car Stereo Review) and check out the ads. Gotta get me
one of those dedicated, gold-plated alternators! 8^)
 
 > You may need an alternator rated to provide higher amps than what you
 > have. The battery terminals are probably the best place to check the
 > voltage. Also check the voltage at the alternator output to see if there
 > is a significant difference. Its possible that cable/terminals/ground
 > contacts are dirty/corroded causing a voltage drop.

If it is voltage drop that's causing the problem, it would seem to be serious
enough that if it affected the main supply (alternator/battery), other 
major electrical problems would exists. Are there any other?

 > I presume you have a powerful aftermarket stereo. If your stereo is stock,
 > then I'd suspect bad cable contacts first, then the alternator's voltage
 > regulator, the alternator's output and the voltage regulator for the gauges,
 > in that order.

Also, check any and all wiring, contacts, fuses and noise suppressors between
the main fuse block and the power point-of-entry at the dash.

DUMB ANALOGY MODE: ON
The loose analogy I use for voltage drops is "rivers and creeks". The battery
cable is the river and everything downstream of the fuse block are creeks.
The size of the cable is the width of the stream/river. The radio is one of
the "drains" under the creek, consumming water. If the drain is large enough,
the creek will drop its level (voltage), so all the drains on that creek
will see an affect of this drop. But the river still flows strong. Bad 
wiring and contacts are like dams, but I'd better stop now because the 
analogy is breaking down fast. Advance apologies to all the EEs out there.

This may confuse you or help you decide where to put the volt meter. Since
they don't drain much, you can use thin wire to get to that point. Just fuse
the wire at the upstream end in case it shorts out somewhere.

Oh, one other thing. Not to assume anything, voltage drops apply to the
ground path, too.

 > -Zafer

-- Eddi