Low voltage issues

[rum66runner]

while i'm driving my truck's voltage will be anywhere from 7-15 usually on the low end and when i pull up to stop sign and get back into first and take off it will shoot back to 13-14 reving usually has no effect on voltage. i'm guessing voltage reg (which sucks cause it's internal) i've check all grounds

replaced:
alternator wire harness
re ran a few grounds to better spots
removed 300 watt amp that was in the truck when purchased
new battery cables w/ brass ends.

i've had 2 different alternators on it but both were old (both around 80k)
just built motor and tranny back in july didn't notice the problem until coming back from lake where my orignal alternator's power cable post broke off and i switched to my spare.

also my temp sending unit is getting high voltage and making my truck read hot when it isn't. guage reads proper when voltage is at 13 volts.

truck is a 92 x-cab 5spd. thanks for looking

 

[Original_Ranger84]

Does it have an external voltage regulator? I know my 84 did.

 

[srteach]

Check the following:

1. Battery Voltage with engine off (should be about 12v)
2. actual alternator output when running (idle and running speed should be about 14v)

If those are good, then double check wiring, and clean batt terminals
If wiring is good and regulator is external to alt, replace it

 

[rum66runner]

greatly appreciate the correction on the voltage regulator i'ma give that a shot tonight when i get outta work. battery volt is good and so is the alternator output.

 

[rum66runner]

alright my volt reg was bad but it's still doing it. when i put on the one (i had gotten many) from the junkyard truck didn't have any issues minus a maf code (forget to plug back in) for about 2 hours of driving went right back to doing what it was doing although i will say the battery light isn't coming on now when it dips and it holds voltage alot better still drops down as soon as i turn on blower motor though.... any idea's? i'm getting the same issue on a 95 merc sable 3.0 just worse....

 

[evanesce69]

have you load tested the battery?

it may hold 12V, but the amperage it can supply can be very low.

 

[rum66runner]

batterys been load tested with a load tester and an arbst tester i've got a good diaode pattern from the alternator when tested it's always around 13-14 but when driving i can tell the trucks only at around 9-10 warranty swapped my battery. If it helps I work at autozone and R&R and diagnios for a Transmission shop when i'm not there. But i'm stumped it's been doing this since september 18th when somehow one way or another the post broke off the back of the other alternator coming home from a fishing trip(150 mile round trip) and it's been doing it since

 

[rum66runner]

Resolved? Truck had a massive short when i went out to start it to go to work two days ago. pulled all of my starting system wires out (positive & negitive battery cable signal wire and anything hooked up to the solinode) was shorting out at the signal wire when it happened. Anyways Ran new wires with new ends. Fired the Truck up it was charging and idling right where it should be temp gauge was good along with oil pressure. Thought i'd share if anyways happens to be having the same problem or research a problem similar to this in the future.