Voltage issues

[Larox37]

Okay guys so I have quite the puzzle going on. I have a 1995 gmc seirra k1500 with a 5.7 tbi, and 4l60e.
My issue is that the cab of the truck is having low voltage. So I tested the battery, alt. And they both work fantastic. Inside the cab however is another story. I have a voltage display on an inveter running of my cigarette lighter and both the dash and the display will drop down to sometimes 8 volts when I have the headlights on, move the plow, even just going down the road. I tried having headlights off and will still do the same thing. The headlights do seem to make it more noticbke though the radio has cut out before many times when it drops thay low. Battery cables are tight on the battery and seem in good shape with no cuts, burns, or anything. In really at a loss but I can't keep having the cab be such low voltage. Is there a ground in missing or something like that Maybe? ANY advise woukd be amazing. Battery stays at good voltage when the cab is low voltage as well. Any ideas?

 

[east302]

What is your voltage at where the battery cable connects to the fuse box on the driver side? It should be nearly identical to battery voltage. Is your alternator voltage (at the alternator and at the battery) 14V or a hair more?

The instrument cluster is grounded on the round bar under the dash, kind of near the parking brake and next to the under dash light bulb. Then there is the ground at the harmonic balancer, one behind the block near the transmission dipstick tube and one at the fender right at the battery. I’m sure there are more, but that’s what comes to mind.




Sent from my iPhone using Tapatalk

 

[Larox37]

I didn't Check the voltage by the fuse block but I can check it tomorrow. And the voltage putting out was I think 14.7 or 14.8 so the alt. Is putting out good. I'll go ahead and check the grounds and the voltage by the fuse block when it's daylight. Do you think it could be a positive cable issue?

 

[east302]

I was thinking maybe you had excessive drop across that cable to the fuse box. Alternator numbers look good. Do they ever drop to the 8V? Are the headlights dimming when this happens?

I would not necessarily trust the dash gauge. Does it do this with the inverter unplugged?

Try seeing how the alternator voltage reading changes when turning various accessories on, maybe you can isolate the big draw.




Sent from my iPhone using Tapatalk

 

[laidbackbigun]

Bud i went thru exact same issue i had 14 volts every place but the dash gauge. So installed a voltage gauge using the ground for the radio and off a ignition hot wire. Still same issue. For a laugh i took ground from aftermarket gauge and put it to bare sheetmetal and it jumped right to 14 volts matching underhood. So i knew my dash had lost its grounding. Sure enough after poling around i found the round bar ground was loose. Cleaned up and tightend and no more issues

 

[WILWAXU]

Bud i went thru exact same issue i had 14 volts every place but the dash gauge. So installed a voltage gauge using the ground for the radio and off a ignition hot wire. Still same issue. For a laugh i took ground from aftermarket gauge and put it to bare sheetmetal and it jumped right to 14 volts matching underhood. So i knew my dash had lost its grounding. Sure enough after poling around i found the round bar ground was loose. Cleaned up and tightend and no more issues

Where exactly is that ground? Not currently having an issue.. but, old truck and I want to make sure I don't

 

[Larox37]

Okay so just checked the volts at the block and it's same as the battery. 14.6 about. I poked all fuses and they all had the same amount in the block on the drivers side too. It's most noticible when I turn the headlights on the cab power goes down on the dash and my inverters display. Im not just bassing it off the dash in basing it off the stereo sitting down and the innjnverters digital voltage display. In not too sure what else therr is too Check..

 

[east302]

Where exactly is that ground? Not currently having an issue.. but, old truck and I want to make sure I don't

This is on a 98. Parking brake is to the right.

You must be registered for see images attach

Sent from my iPhone using Tapatalk

 

[east302]

Okay so just checked the volts at the block and it's same as the battery. 14.6 about. I poked all fuses and they all had the same amount in the block on the drivers side too. It's most noticible when I turn the headlights on the cab power goes down on the dash and my inverters display. Im not just bassing it off the dash in basing it off the stereo sitting down and the innjnverters digital voltage display. In not too sure what else therr is too Check..

I wonder, if you disconnect the cigarette lighter and check the voltage at the connector to a ground, is it closer to 12V?

Maybe try cleaning that ground on the rail (photo in previous post). I’m not sure if that is where the lighter is grounded, but the cluster ground is there.


Sent from my iPhone using Tapatalk

 

[Larox37]

Well good news I am not sure where or why it isn't grounded but I hooked jumper cables from the negative of the battery to a random looking bolt on the body and it worked right away so there must have been a broken ground somewhere somehow? One maybe I didn't see but that was the fix thanks for the help guys been bothering my like crazy and the snow doesn't help. Hopefully this helps someone