Re: [Amc-list] volt meter needle jumping around

[Tom Jennings <tomj@xxxxxxx>]

On Wednesday 01 August 2007 07:19:45 hydeparker@xxxxxxxxx wrote:

> I have a '69 Scout that has a weird quirk: the volt meter needle bounces
> all over the place.  This is a stock, in-dash volt meter, not an
> after-market job.

> Ideas on what to check?  I could check with the Scout guys, but they're not
> as nice as you guys!

Does the voltage bounce UP over 14V? If so, fix this ASAP as it's eating your 
light bulbs, batteries and electronics.

Is there any pattern to the bouncing? RPM related? 

Without having seen it, I would guess the following items in decreasing order:

* Electrical connections between alt and reg
* If this is a 'one wire' (really, 3 wire) modern alt it's the stupid plug 
gone bad
* regulator not well-grounded
* ground wire from alternator to chassis off or loose
* Wiring
* regulator
* Wiring

The alternator/regulator has an internal voltage reference (a zener diode), 
and measures the battery voltage, compares the two, and adjusts output 
accordingly. What happens is, when a connecting wire gets crapped up (loose, 
corroded, etc) its electrical resistance goes up, the alt/reg thinks sees 
that as the battery voltage low, and cranks up alternator output. If the 
battery is actually OK it cooks the battery.

Any push-on connector is immediately suspicious. Take 'em off, wire brush the 
flats, crimp slightly, it ought to be SHINY and TIGHT. You should be able to 
PULL HARD on the wire in the connector. The wire should be TIGHT in the 
crimp. 

Factory crimp connectors, especially those with thew molded black rubber, are 
usually of amazingly good quality crimps. I've taken them apart to look. 
Unless one is realyl lousy it's probably OK inside. Clean, tighten, 
reinstall.

Also of CRITICAL importance are electrical grounds. The tin can of the 
regulator is an electrical connection. If it's loose you're screwed. Take it 
off, sand or wirebrush it SHINY, includin the spots on the firewall/fender, 
if the screws are loose go one size larger or use a screw and nut, and make 
it TIGHT. Hell make all two, three, four tight. Redundancy never hurts!
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