Idiot Lights to Gauges

[Bmstd]

1985 Chevrolet Fleetbed SB project.

I am converting an old C10 Custom Deluxe 4.3 V6 to a 350 V8 and want to swap from the original idiot lights to a stock gauge (no tachometer).

I have swapped the correct sending unit for oil pressure and water temperature into the truck. When i tried to plug in my old sacraficial gauge set nothing worked as I hoped it would. the temp and oil both pegged out and the blinkers are definately not right.

Can anyone lend some insight to sorting out the wiring for this swap?

Thank you,

[ray_mcavoy]

See post #3 by hatzie in this old thread --> http://67-72chevytrucks.com/vboard/s...d.php?t=491032 That should help you figure out the wiring differences between the warning light vs. gauge clusters.

[Bmstd]

Thank you for the link. This will get me where I need to go!

[motornut]

I went from 78 idiots to gauges with tach,you will have to repin the plug
even the location of the light to gauges changed
yes the blinkers wires need to move, as do the neg/pos for the cluster
this is K78 idiots and K79 gauges only.

[Bmstd]

OK, i have re-pinned all the wires and added the one additional positive and negative pin to the plug.

However, i am experiencing the oil pressure gauge is wanting to peg over past 60psi at the 3:00 position. When i unplug the sending unit on the engine, it will at least stop trying to push the gauge the any further.

Has anyone else experienced this? I used a new Standard PS154T (single terminal) sending unit and am questioning that this is any good or if i may have further issues or possibly damaged the gauge. Just as FYI, i have another gauge set i have tried as back up to validate the set i am using.

Thanks,

[ray_mcavoy]

Originally Posted by Bmstd

However, i am experiencing the oil pressure gauge is wanting to peg over past 60psi at the 3:00 position. When i unplug the sending unit on the engine, it will at least stop trying to push the gauge the any further.

The electric oil pressure gauge uses the same type of meter movement as the fuel gauge and can be tested using the same basic procedures.

With the sending unit wire unplugged, the gauge should read maximum pressure (or a bit beyond). Temporarily grounding the sending unit wire should make the gauge read zero (or close to it).

Originally Posted by Bmstd

Has anyone else experienced this? I used a new Standard PS154T (single terminal) sending unit and am questioning that this is any good or if i may have further issues or possibly damaged the gauge.

That is the correct sending unit to be using with a 60 PSI gauge. You can make sure the sending unit is okay by testing it with an ohmmeter. With the engine off (zero pressure) you should get a reading in the zero to 27Ω range (that's with the meter connected between the sending unit's terminal and ground). And with the engine running you should get a higher resistance reading ... up to about 90Ω depending on the actual oil pressure.

Originally Posted by Bmstd

Just as FYI, i have another gauge set i have tried as back up to validate the set i am using.

If you are experiencing the same oil pressure gauge problems with both gauge clusters, that seems to indicate a wiring issue.

And speaking of that, I believe the 4.3 V6 that was originally in your truck would have been equipped with an electric choke. The factory electric choke wiring was routed through a 2-terminal oil pressure switch so the choke would only receive power with the engine running. That same switch was also used to operate the "OIL/CHOKE" light in the warning light clusters. So simply re-pinning the cluster end of that wire would still leave the other end tied into the electric choke circuit. That could possibly be back-feeding power to the sending unit circuit and causing the gauge peg to the 3 O'Clock position.

[motornut]

Originally Posted by Bmstd

OK, i have re-pinned all the wires and added the one additional positive and negative pin to the plug.

However, i am experiencing the oil pressure gauge is wanting to peg over past 60psi at the 3:00 position. When i unplug the sending unit on the engine, it will at least stop trying to push the gauge the any further.

Has anyone else experienced this? I used a new Standard PS154T (single terminal) sending unit and am questioning that this is any good or if i may have further issues or possibly damaged the gauge. Just as FYI, i have another gauge set i have tried as back up to validate the set i am using.

Thanks,

Thats what I used ,no "T" tho,no probs

[chengny]

I checked both terminals of the oil light/e-choke plug and the tan wire is live when key is on. everything else is has no current. However, i noted that the large plug for oil light/e-choke also contains a blue wire running into the center of the plug. Not sure what this wire is doing since there is only two terminals on underside and i do not have an extra blue wire going to the gauge cluster plug.

If a person hasn't looked closely at the schematics, I can see why it would look like the plug goes to a 3 connector switch. There are 3 leads entering the back of that snap-on connector. A pink/white, a light blue and a dark blue.


The power supply is on the pink/wht (it maybe faded enough to look tan). The light blue (goes over to the choke heater) and the dark blue (runs back to the instrument panel to extinguish the "CHOKE"/low oil pressure warning light).

The light blue and the dark blue are spliced together inside the connector body which makes it look like a 3 stab plug. But it is just power in on the pink/wht and out on the two blues:





When the switch is closed the PNK/WHT supplies power to the LT BLU & DK BLU leads - which are connected to the choke heater and the negative side of the CHOKE light respectively.

So, when the engine is started - and oil pressure hits about 10 psi - the oil pressure switch contacts close, the choke heater begins to assist the choke opening and the CHOKE light on the dash goes out.