Tampa 928s

Added a couple of relays for the air and fan noticed today that the voltage gauge reads much lower than before 11.5 or so. I placed a meter on the front post it read 13.9 at idle with air on or off. I added the power to the relays from that post and grounded them to the engine host hook. Every thing works did I dislodge something?
Where is the voltage meter getting its reference from?

mark kibort

obviously its not calabrated, or its coming from a referene with a big voltage drop across it!
mk

BrianG

What was it reading before?

I had an incongruity like that with my car and saw less than .5v difference when measured across the battery and the voltage meter contacts using the same digital meter.

If you remove the binacle and dash unit you will see that there is a trimmer potentiometer in series with the dash volt meter. Not the most sophisticated system... and notoriously inaccurate in our cars.

PS.... tap the instrument plexi-glass firmly with your finger and see if the voltage meter jumps up a little.....

docmirror

Common problem. Thje gauge is not very accurate, and it's sensing point is not very good. I get wierd readings on mine dependent on whether the lights are on/off, AC on/off, heater, etc. Since you measured 13.9 with a DVM at the post, that tells you that the charging system is funtional. Really, that's about all you can do with the dash gauge. If the charging system goes away, the gauge will head for 10V pretty fast and drop continuiously no matter what acc you use.

Tampa 928s

What is odd it worked fine untill I added the Relays.

BrianG

That'll learn ya!!

LT Texan

My theory is that on mine the wires supplying the power to the fuse panel have become highly resistive with age and need replacing. I'm going to test that theory soon by hooking up a multimeter at the battery, the alternator, the starter and then the fuse panel and see if I can deduct that this is true by the readings. And if it is....

Dan Perez
78 5 speed

Alan

Seems odd - are you sure of your meter - battery in it is good?

report on what voltages you see at the battery at the rear rear and at the jump post and at the top of the CE panel (the 2 bolts under the hinge up plastic cover)...

The pod Voltmeter is essentially from the CE panel. You have added some big loads on the wire to the CE panel from the Alt so this may have reduced the voltage there a little (but if its really at @ 13.9v at the jump post this seems OK)

Alan

Tampa 928s

Meter is a fluke battery is fine!
Starting to rain dont want to get smoked in the garage, but I am going to the battery directly My posts look fine in the panel just put it back in last week I took the reading from the front post on the fender well as well as added the relays to this post. I will unload the relay and check it. I would rather not tear under the panel again its reading around 11v a little more when driving but not where it was. I think this happened after my relay install but it could of been before when I did all the work on it. I started looking at the gauge after you scared me on the load when starting.

RicerSchnitzzle

Not only is the gauge not the most accurate but the needle is just pressed onto the pin. If at any time it has been nudged when pod was apart, the zero point has changed. Good news is you can gently nudge it below zero when off to show a higher reading. A little trial and error and you can get to match the 13.9v. I messed my up putting on glow gauge face plates. Easy to fix once I figured out what happenned.

dr bob

Tampa--

Move the ground from the engine hoist bracket to a chassis ground point.

Move the ground reference you are using with your Fluke back and forth between the frame ground and an engine ground (like that bracket...) and you'll likely be able to see a difference, depending on charging current and the condition of the ground strap that connects the frame to the engine. Older cars, humid or corrosive or reactive (salt water nearby?) environments play hard on that copper braid ground strap. Peek underneath and find the strap between the frame rail on the pass side and teh engine block. Is it a little green from chloride reaction? Time for a new one! A bad ground strap will play hell with all sorts of engine sensors and functions. Could easily be on a PM list. Might also be a candidate for a lug-to-lug insulated 2-ga battery cable replacement, although the insulation will hide deterioration that does occur.