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73-87 Chevy _ GMC Trucks => Electrical => Topic started by: kjnmontana on July 31, 2020, 06:10:25 PM
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Howdy folks, I have a self inflicted wound I’m asking some help on. Background: cleaning up engine bay wiring and failed to take good enough pics to help me return everything back to it’s proper place, specifically the stater/ignition system. 1989 V3500 with LE8 454, carbureted, manual. I’m referencing the wiring schematic for R,V and P models (1989) pages 3 and 18. One of the issues I’m having is the wiring diagram does not show how the starter relay is factored into the system. I’m also struggling with what ties into the junction box on the firewall. And finally, and most embarrassingly, for the life of me, I cannot figure out where to return the 2 red wires coming off the starter solenoid. I see where the battery negative and positive go, but these two heavy gauge wires are a mystery to my simple mind. Is there a diagram that would take my hand and show the wiring from the pass through block to the distributor, junction box, starter relay, starter and battery, you know something a second grader could follow? Thanks
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The Battery Positive cable and the two eyelet terminals for the fusible links attach to the same stud on the starter solenoid.
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Got it, now working back to the relay, junction box, distributor...
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BD, so where do those 2 wires go to?
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Ok, it’s starting to dawn on me relooking at the wiring schematic, one comes from the junction box and the other from circuit 2 on the engine pass through block, correct?
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Unless someone added one after-the-fact, there is no standalone starter relay. The ignition switch energizes the starter solenoid directly via the purple wire (Ckt 6). The two red wires connect to the firewall junction block and the firewall pass-through bulkhead connector (both Ckt 2). See image.
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BD, thanks so much for the enlightenment. Another question regarding the fusible links, it shows 2 different gauged wires connected by an incased fuse. Where can I find this style or have they been replaced by the inline fused version and if so, what gauge wire and fuse size is recommended?
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Another question regarding the fusible links, it shows 2 different gauged wires connected by an incased fuse.
What shows this ^^^^ ? Certainly not the factory schematic I posted. If you need to replace a fusible link, refer to How to change a Fusible link (http://forum.73-87chevytrucks.com/smforum/index.php?topic=11972.msg45217#msg45217) by VileZambonie. Read through the entire process before you begin.
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That’s how I interpreted the 1989 Wiring Diagrams R-V and P Trucks Models Manual. Page 2 describes the wire annotation as; Wiring Circuit Number, Wire Size as in SG. MM. and Color of Wire. So on Page 18, Circuit 2 wire on the Firewall Bulkhead Connector is a 3.0 Red or a 12AWG Red that is sliced into a 1.0 Red Thermal HW Fusible Link (16 AWG) that is connected to the Starter Solenoid. I’ve read your Fuses and Circuit Protection piece as well as VZ’s How to Make a Fusible Link. Am I misinterpreting something?
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That’s how I interpreted the 1989 Wiring Diagrams R-V and P Trucks Models Manual. Page 2 describes the wire annotation as; Wiring Circuit Number, Wire Size as in SG. MM. and Color of Wire. So on Page 18, Circuit 2 wire on the Firewall Bulkhead Connector is a 3.0 Red or a 12AWG Red that is sliced into a 1.0 Red Thermal HW Fusible Link (16 AWG) that is connected to the Starter Solenoid. I’ve read your Fuses and Circuit Protection piece as well as VZ’s How to Make a Fusible Link. Am I misinterpreting something?
Except for a few typos, this ^^^^ is perfect! ;)
Another question regarding the fusible links, it shows 2 different gauged wires connected by an incased fuse. Where can I find this style or have they been replaced by the inline fused version and if so, what gauge wire and fuse size is recommended?
However, this ^^^^ is not. Where do you see an "encased fuse" on the diagram? ???
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Sorry, that was my attempt at trying to describe what I thought was inside the fusible link’s molded rubber section...what is inside there?
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I assume it’s just heavy protection for where the two wires are connected?
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I think you are referring to the molded urethane encasement that completely encloses and seals the parallel splice that joins the two wires together end-to-end. When it becomes necessary to replace the fusible link, that splice with its urethane encasement is severed from the wire bus. A new 6" long fusible link of the appropriate gauge is then crimped and soldered onto the end of the wire bus. Finally, the splice is entombed in marine grade, adhesive lined, dual-wall polyolefin heat shrink.
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Thanks, the education continues!
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BD, I’m cleaning up the oil pressure sensor (OPS) wiring and once again trying to interpret the proper wiring diagram for my 1989 V3500, carbureted 454 manual tranny. I have a Holley 4BC with electric choke with a single ~18 AWG wire (not sure where it is suppose tie into), and the OPS with a single ~18 AWG Tan wire going to circuit 31 on the Firewall Bulkhead Connector and two wires (~ 18 AWG) coming from what I assume is the electric choke OPS. The electric choke OPS is attached to the OPS just below the oil filter. One of the wires from the electric choke OPS is connected to circuit 39 on the Firewall Bulkhead Connector which I believe is the Hot in Run and Start Fuse. Not sure where the second wire goes...Thanks.
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Regarding the choke, read through GM electric choke operation (http://forum.73-87chevytrucks.com/smforum/index.php?topic=36868.msg309686#msg309686). The choke OPS should have two prongs and three wires, pnk/wht (ckt 350, choke power from the CHOKE fuse), lt blu (ckt 78, choke heater element), and dk blu (ckt 931, instrument cluster choke indicator lamp). I don't have a factory diagram of the 1989 choke circuit that definitively shows which bulkhead connector cavities serve which wires.
See the two images below for the engine oil pressure gauge wiring. The gauge OPS has one prong with a single tan wire (ckt 31).
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So, the three wires off the bulkhead circuits going to the two prongs on the choke OPS (does it matter how they are paired?). How does the choke wire tie in with the choke OPS?
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Did you study the article (GM electric choke operation) previously linked? The two blue wires share one terminal of the choke OPS, the pink w/white stripe wire connects to the remaining terminal of the choke OPS.
Only two wires route to the bulkhead pass-through connector - pink w/white stripe and dark blue. The light blue wire connects to the choke heater element on the carburetor.
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I did study the GM electric choke operation diagram and noted that the light blue wire connected the choke heater to the choke OPS.
What is confusing is that you stated the light blue wire is associated with circuit 78 as well as being used to connect the choke heater to the choke OPS.
As it stands, I have the two blue wires (circuits 78 and 931) coming off the bulkhead pass through connector as well as the pink/white coming off circuit 350. These will be connected to the two prong choke OPS as you described.
According to GM choke operation diagram, the light blue wire is then used to connect the choke heater and the choke OPS which makes it seem like the choke OPS has a forth wire being connected to it.
You also said “Only two wires route to the bulkhead pass-through connector - pink w/white stripe and dark blue. The light blue wire connects to the choke heater element on the carburetor.” I clearly have the light blue wire coming out of the bulkhead pass through connector as well so I’m struggling with the light blue wire’s routing.
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Perhaps there is more to the story for 1989 models. I did not find a wiring diagram that illustrates the 1989-specific choke heater circuit. Where does the wire that connects to the choke heater run? Did you trace it?
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That’s the problem, the electric choke heater wire wasn’t connected when I dove into the wire cleanup and the choke OPS connector was fried and hanging off the OPS sender fitting making it darn near impossible to see how it was configured...
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So use a test light and meter to decipher what those wires do. Keep a cool head, apply some logic and before you know it, you'll have your answers. Determine which wire illuminates the instrument cluster choke lamp when grounded, which has ignition power, where the "extra" blue wire goes inside the cab, and why. It shouldn't be too difficult to sort out.
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Unfortunately the instrument cluster is pulled from the dash as is the majority of the cab’s wiring so circuit continuity checks are limited. I was able to see the other side of the bulkhead pass through connector and saw only the dark blue wire exiting the 78/931 circuit slot and terminating at the instrument cluster loom connector leading me to believe it is the circuit 931 choke indicator lamp source. Not sure what the other wire does/did, but I can now complete the the choke OPS and choke heater connections. Thanks