Coupla wires that I don't know where to put.

[THE "10" SILVERADO]

Could anyone identify any of these wires? I believe the one with the white connecter in the first pic is for my distributor, but the other two wires were not hooked up before (I don't remember undoing them). The other one in the 1st pic looks like it should plug into a spade somewhere on the drivers side and the wire in the 2nd pic goes to the passenger side. All of my a/c wires are accounted for so I don't know what these are.

Mystery wire in 1st pick (I think) is green.
Mystery wire in 2nd pic is blue.

[Tx Firefighter]

First picture are the HEI wire and the oil pressure sending unit wire. Both are located very near each other on the back of the engine. If the HEI wire was truly never hooked up while you've owned the truck, it's probably a tach signal wire which plugs into the distributor cap directly next to the HEI power wire.

[THE "10" SILVERADO]

Originally Posted by Tx Firefighter

First picture are the HEI wire and the oil pressure sending unit wire. Both are located very near each other on the back of the engine. If the HEI wire was truly never hooked up while you've owned the truck, it's probably a tach signal wire which plugs into the distributor cap directly next to the HEI power wire.

The white connector in the first one goes to my dizzy. I checked some pics of the teardown and saw it. I have a mechanical oil pressure gauge so is there anything else could that second wire be? Thanks.

[ont_guy_38]

It's possible your truck was switched to mechanical at some point as that looks like oil pressure to me also. I thought only 73-76 had mechanical but not sure.

[Tx Firefighter]

Originally Posted by ont_guy_38

It's possible your truck was switched to mechanical at some point as that looks like oil pressure to me also. I thought only 73-76 had mechanical but not sure.

Agree. I've been sitting here trying to figure out what else it could be, but that rubber shrouded wire is an oil pressure sending unit connection. I'm pretty sure of that.

[THE "10" SILVERADO]

Hmm, well considering some of the other things I've found on this truck it wouldn't surprise me if something was changed over during the last couple of owners. Any ideas on the wire in the second pic? It looks like some sort of fancy connector that would slide onto a spade as well. Thanks.

[Tx Firefighter]

Possibly fast idle solenoid on the carb for air conditioning.

[THE "10" SILVERADO]

Originally Posted by Tx Firefighter

Possibly fast idle solenoid on the carb for air conditioning.

That makes sense. The 2bbl carb with the idle solenoid is long gone. Guess I don't need that wire anymore. Thanks.

[ont_guy_38]

Originally Posted by Tx Firefighter

Possibly fast idle solenoid on the carb for air conditioning.

Yup I agree.

[motornut]

Originally Posted by Tx Firefighter

Agree. I've been sitting here trying to figure out what else it could be, but that rubber shrouded wire is an oil pressure sending unit connection. I'm pretty sure of that.

yup looks like the oil one in the 78
was idiot (in pic)now gauge

[ray_mcavoy]

Originally Posted by ont_guy_38

It's possible your truck was switched to mechanical at some point as that looks like oil pressure to me also. I thought only 73-76 had mechanical but not sure.

The mechanical oil pressure gauge was still stock equipment in 77 (last year for it though).

I agree, that black rubber boot type connector is definitely for an oil pressure switch. So it's still possible that it's been converted over from warning lights to gauges.

Another possibility would be that the factory used the same engine harness for trucks with & without factory gauges and just left that oil pressure wire unused on the trucks with gauges. If I get a chance tomorrow, I'll go check my 77 (with factory gauges) and see if it has an unused oil pressure light switch wire/plug in there. I could see them doing this for 76-up because these years used voltmeters so there wouldn't be any ammeter wiring necessary. And the same temp switch/sender wire could be used for either a light or gauge signal.

[88Jimmy4x4]

Originally Posted by THE "10" SILVERADO

I have a mechanical oil pressure gauge so is there anything else could that second wire be? Thanks.

That blue with boot connection is for oil pressure sending unit. My 76 is all original with the mech gauge but mine too has that connection that is unused. GM didnt make a diff engine harness for that, however there will be no power to it since it wont be connected via the overlay on the gauge assembly....I have checked mine....just let it hang behind engine.

[ray_mcavoy]

Originally Posted by ray_mcavoy

Another possibility would be that the factory used the same engine harness for trucks with & without factory gauges and just left that oil pressure wire unused on the trucks with gauges. If I get a chance tomorrow, I'll go check my 77 (with factory gauges) and see if it has an unused oil pressure light switch wire/plug in there.

Originally Posted by 88Jimmy4x4

That blue with boot connection is for oil pressure sending unit. My 76 is all original with the mech gauge but mine too has that connection that is unused. GM didnt make a diff engine harness for that, however there will be no power to it since it wont be connected via the overlay on the gauge assembly....I have checked mine....just let it hang behind engine.

Yup, I checked my 77 and it's the same way ... just has that blue wire with the rubber boot connector hanging loose back there.

One thing I did find interesting to note is that the 77 gauge clusters (at least the 4x4 ones anyway) do have an "OIL" light at the bottom of the speedometer right next to the 4 wheel drive light. On the spare 77 cluster I checked, it even had a bulb in there and has traces on the printed circuit leading back to the cluster connector (same pin as the oil light on a non-gauge cluster). And if I'm reading the 77 wiring diagram correctly, it looks like it might already be wired up to that unused blue wire/plug behind the engine. Looks like I could add a Tee fitting, pressure switch, plug the wire in, and end up with both a gauge & an oil light.

[88Jimmy4x4]

Originally Posted by ray_mcavoy

Yup, I checked my 77 and it's the same way ... just has that blue wire with the rubber boot connector hanging loose back there.

One thing I did find interesting to note is that the 77 gauge clusters (at least the 4x4 ones anyway) do have an "OIL" light at the bottom of the speedometer right next to the 4 wheel drive light. On the spare 77 cluster I checked, it even had a bulb in there and has traces on the printed circuit leading back to the cluster connector (same pin as the oil light on a non-gauge cluster). And if I'm reading the 77 wiring diagram correctly, it looks like it might already be wired up to that unused blue wire/plug behind the engine. Looks like I could add a Tee fitting, pressure switch, plug the wire in, and end up with both a gauge & an oil light.

that would be nice, I know on my 76 the wire is in the harness but no connection via the overlay. I wanted to use that wire for my elec choke but it has no power. Could you check yours and see if it indeed has any voltage to it?

[ont_guy_38]

Originally Posted by ray_mcavoy

Yup, I checked my 77 and it's the same way ... just has that blue wire with the rubber boot connector hanging loose back there.

One thing I did find interesting to note is that the 77 gauge clusters (at least the 4x4 ones anyway) do have an "OIL" light at the bottom of the speedometer right next to the 4 wheel drive light. On the spare 77 cluster I checked, it even had a bulb in there and has traces on the printed circuit leading back to the cluster connector (same pin as the oil light on a non-gauge cluster). And if I'm reading the 77 wiring diagram correctly, it looks like it might already be wired up to that unused blue wire/plug behind the engine. Looks like I could add a Tee fitting, pressure switch, plug the wire in, and end up with both a gauge & an oil light.

I was going to say that ,but thought maybe it was just my old age kicking in (not remembering real things...lol). When i had my shop, I worked on tons of the older Chevys and I kinda remember seeing a few with both a mechanical gauge and a light.The sending unit for the light used to be sideways behind the distributor infact, I think my Dads' 73 was one of them.

[88Jimmy4x4]

Originally Posted by ont_guy_38

I was going to say that ,but thought maybe it was just my old age kicking in (not remembering real things...lol). When i had my shop, I worked on tons of the older Chevys and I kinda remember seeing a few with both a mechanical gauge and a light.The sending unit for the light used to be sideways behind the distributor infact, I think my Dads' 73 was one of them.

I dont see how you could have both behind dist, the mech gauge fitting screws into same location as a sending unit does.....I think its one or the other not both from factory, its just wired for it in case you need it to keep the engine harness same no matter what.

[ont_guy_38]

Ya not saying it came like that from factory, just remember something like that in the back of my mind. Was probably owner added at one point

[motornut]

found the pics after
in the 78 Jimmy I used an elbow,to fit the gauge sender

[ray_mcavoy]

Originally Posted by 88Jimmy4x4

I dont see how you could have both behind dist, the mech gauge fitting screws into same location as a sending unit does.....I think its one or the other not both from factory, its just wired for it in case you need it to keep the engine harness same no matter what.

Originally Posted by ont_guy_38

Ya not saying it came like that from factory, just remember something like that in the back of my mind. Was probably owner added at one point

While I don't think I have ever seen a factory setup with both a light and gauge, I have hooked a number of them up like that myself. Here's a mock-up of the configuration I used in my Nova to add an oil pressure gauge while keeping the original warning light functional. Seems like I did have to re-orient the Tee fitting sideways for distributor clearance after swapping in an HEI though.

Originally Posted by 88Jimmy4x4

that would be nice, I know on my 76 the wire is in the harness but no connection via the overlay. I wanted to use that wire for my elec choke but it has no power. Could you check yours and see if it indeed has any voltage to it?

I've still got that on my to-do list.

Although my 77 GMC doesn't have an electric choke, the wiring diagrams show that some 77 engines did come with them from the factory. And the wiring diagrams show it making use of that dark blue "oil light" wire along with an additional orange or brown/white wire (depending on the engine). Both wires lead to a 2-terminal oil pressure switch and a single light blue wire (hooked to the same terminal as the dark blue wire) runs from there to the electric choke heater. It looks like that orange or brown/white wire is the actual power feed wire and the dark blue one is still just for an indicator light. Although I'm guessing those trucks got a slightly different instrument cluster with a lens over the bulb reading "choke" instead of "oil".

[ray_mcavoy]

Originally Posted by 88Jimmy4x4

that would be nice, I know on my 76 the wire is in the harness but no connection via the overlay. I wanted to use that wire for my elec choke but it has no power. Could you check yours and see if it indeed has any voltage to it?

I finally got around to checking it and my 77 does have voltage on that unused dark blue "OIL" light wire with the ignition on. It's not a direct power feed though ... it's going through the bulb filament. So temporarily grounding the terminal behind the engine makes the "OIL" light come on. Looks like they had it pretty much all wired up from the factory and just stopped short of sticking in a Tee fitting & pressure switch.

Here's a pic of the back of a spare 77 gauge cluster showing how that dark blue wire is connected to the circuit traces: