View Full Version : Voltage variance

11-06-2007, 03:56 PM
My dash voltmeter has been reading a bit low (12.5-13v) and when i go under the hood to check with a multimeter i get anywhere from 13.8 -14.2 volts. Does anyone else get these variences? If so where could the voltage drop be located? Or could it be the gauge itself? :confused:

11-06-2007, 04:10 PM
Are you sure that you alternator is okay ? I got the same on my truck. Checked everything : Battery cables, each battery tested, serpentine belt tension and tensioner and so on. At least bought a new alternator and all was gone. After starting dirctly 14,7volts at the gauge and after a while driving dropping to 14,4volts. Dissassambled the old alternator and remarked the brushes are gone. Only the rest of a about 1 cm was left.


11-07-2007, 01:22 AM
My volt meter reads wrong, low like yours, they are not accurate.

11-07-2007, 01:52 AM
Same problem on my truck. Bothered my bad until I got under the hood and went over everything w/ a fine tooth comb. Will probably still add a set of manual gauges in the near future.

11-10-2007, 10:00 PM
Mine was reading low the other day, around 12 volts on the gage at highway speeds, so that sparked my intrest and started turning off all my accy's that were on and no difference. Here I am driving home, it's dark out and I'm thinking that i might not make it until!!!!!!!!!!!!! I gave the old dash/ face plate a couple of knocks with the knuckle and that gage popped right up to 14.5 volts. i haven't really found the problem yet but i suspect it's most likley a bad ground under the dash or the harness to the printed circuit on it.

11-10-2007, 10:08 PM
my gauge has done that a couple times, once real bad it said it was only around 10 volts but when i checked at the bat. with a multi meter it was 14.4 both times i fixed it by cleanning the doubled pos. cable, easy fix

11-10-2007, 10:59 PM
The instrument panel, is a big plug, and the contacts are crap and it plugs into a socket at the back, so push on the panel and it moves the contacts. You could remove the instrument panel and clean the contacts, had to do that to mine.

11-11-2007, 12:36 AM
I'll give that a try. I've had the dash apart quite a few times, steel wool to the contacts and some di-electric grease should fix it hopefully.

11-28-2007, 08:41 PM
Well, so far i've cleaned and greased the contacts for the instrument cluster, replaced both batteries, cleaned, lubed and checked the resistance (no more than 0.10ohms) of all my cables and connections, replaced the alternator and i'm still having charging problems. :mad:

When i'm sitting idling the charge will be at 13v but when i turn on everything in the truck it drops to 12.6 and wears down the batteries from there. The voltage drops on the highway too causing a DTC 36.

When i put my multimeter leads directly on the positive output of the alternator and the alternator housing i get a reading of 14.65 for a few milliseconds then drops to 12.96 (when accessories are off)

Anyone?? :confused:

11-28-2007, 09:36 PM
are you getting your reference (field) voltage? And is it constant? Sounds like a voltage regulator. I have had bad ones right out of the box. Do you have a shop nearby that can put that alternator on the bench and check it out independent of the truck? Stuff like this always makes me pull my hair out, too.