95 c1500 gauges drop when i turn on the lights.

[Irondice]

Long time listener first time posting... newly aquired 95 350 tbi... Truck turns on and runs fine. New alternator and battery installed. At idle voltage and oil pressure and temp gauges are normal. But when i turn on the lights or turn signal or just touch the brake pedal all 3 gauges drop a considerable amount. Especially the oil pressure and voltage. All 3 jump with the turn signal click also. Any help would be appreciated

 

[1998_K1500_Sub]

Check the ground straps.

There are two are up front, just behind the passenger's side exhaust manifold.

One strap runs from the back of the engine head to a stud on the body, and the other from the same body stud to the frame. Those form the ground return path for the fuel pump, tail lights, and other circuits.

Too, there also a ground wire that runs from the passenger's side fender to the negative terminal on the battery.

This/these may or may not be the problem, but I believe the problem is related to a ground problem.

The ground straps are something you should check on a vehicle that old, particularly b/c it's "new to you".

 

[Irondice]

Check the ground straps.

There are two are up front, just behind the passenger's side exhaust manifold.

One strap runs from the back of the engine head to a stud on the body, and the other from the same body stud to the frame. Those form the ground return path for the fuel pump, tail lights, and other circuits.

Too, there also a ground wire that runs from the passenger's side fender to the negative terminal on the battery.

This/these may or may not be the problem, but I believe the problem is related to a ground problem.

The ground straps are something you should check on a vehicle that old, particularly b/c it's "new to you".

Thanks I'll have a look at those straps. Also when i remove the wire from the alternator that goes to the gauge cluster the alternator stops whining. And idle goes up slightly and smooths out. And on the gauge cluster it still shows about 11 volts .

 

[1998_K1500_Sub]

when i remove the wire from the alternator that goes to the gauge cluster the alternator stops whining. And idle goes up slightly and smooths out. And on the gauge cluster it still shows about 11 volts .

Hmm... not sure what you mean.

IIRC, there's the multi-pin connector on the alternator (at least on my 1998) and there's the alternator output stud.

If you please: What exactly did you "remove"?

 

[Irondice]

Hmm... not sure what you mean.

IIRC, there's the multi-pin connector on the alternator (at least on my 1998) and there's the alternator output stud.

If you please: What exactly did you "remove"?

Left side arrow in the picture... on mine its a single wire connector. Just figured out that make the alternator charge the battery after my battery voltage dropped to 9 volts.

 

[Irondice]

update. After connecting the ground straps at the back of the motor the lights are bright and working correctly now its a problem of while driving the oil pressure drops and the motor hesitates and stalls out

 

[1998_K1500_Sub]

After connecting the ground straps at the back of the motor the lights are bright and working correctly

That's good news.

now its a problem of while driving the oil pressure drops and the motor hesitates and stalls out

^^^ Umm... what are you saying?

Did this problem just show itself after you fixed the ground straps?

 

[Irondice]

That's good news.



^^^ Umm... what are you saying?

Did this problem just show itself after you fixed the ground straps?

I thought the hesitation was from the gauges dropping so low. But it didn't stall out before. Oil pressure drops when coming to a stop. Fluttering the gas pedal doesn't bring it back. Its starts right back up and makes it a few stop signs before stalling out again.

 

[someotherguy]

Really guessing here as it sounds like your new-to-you truck has multiple demons that need exorcising, but my wild guess is a combination of problems - fuel pump relay bad, as well as oil pressure sender/switch combo bad, causing interruption to the fuel pump circuit. It only takes one of these operating correctly to successfully power the fuel pump circuit, but if both are flaky, there you go. It sounds to me like the truck may be depending on the oil pressure switch and they tend to get flaky where they'll read low/zero.

I'm not 100% sure on this but I think the fuel pump relay on a '95 isn't a common type with any of the other ones in your electrical center that you might swap as a quick test, and while I don't normally like to recommend just shotgun replacing stuff - a fuel pump relay is really inexpensive and may be worth spending a few bucks on just as a test.

Richard

 

[1998_K1500_Sub]

I thought the hesitation was from the gauges dropping so low. But it didn't stall out before. Oil pressure drops when coming to a stop. Fluttering the gas pedal doesn't bring it back. Its starts right back up and makes it a few stop signs before stalling out again.

OK, so we know the oil pressure doesn't depend on the electric circuits, but the oil pressure gauge does. So the gauge may be in error for reasons yet unknown.

We also know that the oil pressure depends solely on the mechanics of the engine, and will drop if the engine RPM drops or dies, or drop if the bearing clearances become excessive, etc. But otherwise, if the oil pressure wasn't a problem before, it's not a problem now. The gauge's performance may have changed for some reason.

As for the engine hesitation, it's time to investigate.

Are there any codes set?

@someotherguy's remarks are noteworthy too.