Why does my voltage guage only show 9-10 volts ?

[Danish Farmer]

Hi gyes

My voltage guage usually points near the red mark at 9-10 volts.
Batteries cranks the starter quickly and it does not seem to lack any electric power.
Some times driving, it will raise to about 12 V, but never above, and the next minut point at 9 again.
My brother checked the alternator, and it pumps out around 12 volts

Planning extra running lights in the frontfender, and put on extra for the long beam.
Shall i worry about the guage ?

Best regards, the ovner of a danish living lonesome Silverado :smile5:

 

[DieselCash]

You should be putting out at around 13.2V to 14V at the back of the alternator. :agreed:

 

[WarWagon]

Shorted battery cell. The bad battery is dragging the entire system down. Have the battery's checked. You want 12.4v -13v at the battery with 12.8v being ideal with the engine off.

 

[JMJNet]

x3, load test the batteries one at a time first.

Is the tach behaving nicely? or erratic?

Also make sure that all the connectors are tight and clean that includes the batteries, grounds, etc.

 

[bison]

my 89 has never shown more than 8-9 volt on the gauge,been like that since i own it (16 yrs).replaced alt once,batts 3 times.

 

[Danish Farmer]

Great, thanks. I will have him measure the batts one by one like u suggest.
Yep, tac is always steady, and all grounds are resently walked thru and renewed

 

[konstan]

Take a voltmeter and measure voltage at any of the batteries. That gauge may be lying, it often does. If the gauge is lying, here's what I did to fix mine.

Take the dash bezel out (it is only held by plastic tabs, pull and it will come right out.
remove the wiring from any switches stuck in the bezel and put the bezel out of the way.
Remove four small screws that hold the instrument cluster
Remove the cluster
Look at the back of the cluster. The voltmeter contacts are metal tabs that need cleaning or are not making firm contact. Clean and/or fix.

This may also be a good time to check the backlighting bulbs and the idiot lights to make sure they all work.

For extra credit replace the back lighting bulbs with LEDs that you can order from superbrightlefs.com, I got blue lights to match my stereo

 

[WarWagon]

I was going off the brother who checked the alternator at 12v... Was this an exact measurement?

 

[konstan]

Right after start, at the alt or batteries (doesn't mater) it will be low - the batteries are charging. Wait 5 min then measure. It should be 13.8 volts.

If its 12 its too low. Alt neefs replaced.

The dash gauge in these trucks is a joke.

 

[Pruittx2]

Huh, my answer when reading the post title was gonna be,,,, Stock gauges suck! That's why.

 

[Turbine Doc]

Only way to check batteries is load check volt meter will only give state of the surface charge every 6.5er or even single battery gasser types with puter controlled vee-hicles IMO needs one of these or similar in their tool kits.

 

[schiker]

Is this something that just started? Mine usually is above 12 near 14 volts on my guage normal driving (after recovery). Blinkers will make it dip as will turning on lights will lower it and all accessories on bit lower too.

If it just started concentrate the most on passenger side positive connection. Take it fully apart. Clean the spacer and 4 faces of wire leads (you have to peel back the rubber covers) and then make sure its tight. Then do other connections and both ends of grounds. Grounds are always suspect on these trucks.

Another place to easily check is the main lugs behind the fuse box under the hood drivers side fender near brakes. If that reads what guage reads then guage is ok I would say.

If it has always read low then the above are just some some checks to see. I think the main lugs at the fuse box should be a good check of the guage itself though.

 

[konstan]

He said the truck did not lack any electrical power... Meaning, I presume, it cranks well and lights aren't dim.
We need a simple voltmeter measurement though.

 

[konstan]

Only way to check batteries is load check volt meter will only give state of the surface charge every 6.5er or even single battery gasser types with puter controlled vee-hicles IMO needs one of these or similar in their tool box

Does HF sell this?
How many amps does it test at? Surely not 700-800?

 

[NVW]

Any load tester I've used only tests the battery at 1/2 it's rated cca. So Tim's would easily test an 800 cca battery.

I believe Tim mentioned getting that at HF.

 

[Burning oil]

My burban does the same thing, Im think its a ground. Have not looked into it yet though.

 

[Danish Farmer]

Folks,

Had my batteries tested seperately tonight, they both shoved arround 12,3 Volts, and the back of the alternator said 13,4 V at idle.
So it must be the guage in the dash thats out of order like one suggest, I guess.

Thank you for the good and interessting replies. Everytime you put a question here, seems like you get to know ten more things about the truck :smile5:

 

[dually boy]

hi there new member im having the same prob. 94 3500td. replaced the battery and the glow plugs only reading 9 amps and drop way down when heater is on and still has probs starting thinking alt

 

[racedaymechanic]

Check all of the grounds, They need to be clean and tight

 

[bshull]

I had the same problem, low voltage readout on the dash gauge. Checking the volts at the alternator netted me 13 volts and change. Batteries tested high 12 volts. The voltage seemed to get worse with long runs down the highway after the engine bay heated up.

As mentioned above I cleaned the grounds with little improvement and I replaced the alternator. No joy, no solution. So I bit the bullet and purchased a battery cable kit from ptwireingsolutions, I also really cleaned the ground surfaces. It worked, now I read voltage on the gauge that is around 14 volts +/-.

So long story short, the factory wiring had run its course and was corroded up, this was verified by me stripping the insulation off and finding corrosion 4 inches from the end of the cable. I encourage anyone with voltage issues to clean the grounds and check their wiring and replace it if you have any question.

That is what worked from me.

Brian