Oil Pressure & volt meter Problems

[JimE]

I have a 1986 C10 Silverado with 4bbl carb. My oil pressure sending unit blew out and I replaced it, but now when ever I put the auto tranny in gear the oil pressure drops to minus pressure and the amp meter goes to -13 volts. When I put the tranny back in park the gauges return to normal.

I have tried switching wire connectors on the oil sending unit, there are no wires near the shifting linkage.

Does anyone have any idea what the fix may be?

[Captkaos]

Sounds like shorted wires

[Irish_Alley]

neutral safety switch problem? does it still act funny in neutral or anything besides Park?

[JimE]

The only time the gauges return to normal is when it is in park. I did notice that when I hit the brake the needles fluctuate, so I'm going to check that out.

Thanks for the help.

[rich weyand]

A multi-system electrical failure is almost always grounding issues.  Check your ground straps.
http://forum.73-87chevytrucks.com/smforum/index.php/topic,26163.0.html

[Irish_Alley]

rich how can putting a truck in gear and causing problems be a ground issue? not questioning your suggestion but curious. the only thing that i can think of that gets power by the shifter is the nss, but then how does that feed back to the dash?

[jaredts]

I had a friend once with a vw that had electrical problems when you put it in gear.  It was grounds between the engine and firewall.  When you put it in gear the engine would shift and loose connection.

[rich weyand]

When you put a car in gear, the rpms go down from idle-in-neutral, the output of the alternator goes down, as one example.  You go through reverse to go into gear, and the reverse lights go on.  There is a "Park sensor" to allow the engine to be started -- maybe that provides the missing ground to make things work when in Park, but not otherwise.  There's three possibilities. 

Basic message: crazy things happen when the grounds are missing.  Check them.

[Irish_Alley]

see that why i was saying nss its the only thing i could think of that would give power in gear but the gauges so return to normal when in neutral

[Irish_Alley]

my brothers 89 iroc was doing something like this. his problem was a loose wire that went to the ecm if you wiggles it it would fix the problem. but this would be a constant problem not just while in gear

[bd]

A multi-system electrical failure is almost always grounding issues.  Check your ground straps.
http://forum.73-87chevytrucks.com/smforum/index.php/topic,26163.0.html

I agree - this is the best starting point.

rich how can putting a truck in gear and causing problems be a ground issue? not questioning your suggestion but curious. the only thing that i can think of that gets power by the shifter is the nss, but then how does that feed back to the dash?

The cab "might" be finding an alternate ground path through the shift linkage.

[rich weyand]

The cab "might" be finding an alternate ground path through the shift linkage.

Or the parking pawl.

[diphthong]

When the problem happens, Isn't this the position of the two gauges the same when the ignition is off.

It's almost as if he's describing losing power to these gauges.  These gauges are simple grounding circuits, You eliminate the power (+) or the ground (-) you eliminate the circuit.  If I'm Correct, and the gauges are mimicking an engine off condition, Because there's two independent circuit, I would start looking for the problem with the positive (+) side not the negative (-) side.










I once had a shop owner tell me "it's possible to have just one plug wire crossed"   :-)