I have a 1987 D250 w./a 318 and a Holley 6280 2 bbl carb which I replaced with exactly the same model rebuilt carburetor. The truck is a California model, equipped with Calif Emission systems. I matched up the new (rebuilt) carb to the old one and there was only 1 vacuum fitting that was a slightly different size... not a problem... otherwise it matched exactly. Unfortunately, when I disconnected the wires of the old unit from the truck, I did not mark or remember the placement of the 5 wires into the 6-way plug at the manifold. I have researched extensively the wiring schematics that are available (which I've found only ONE... the same document in the crappy Haynes manual, as well as the online DIY repair services. This wiring diagram is either incomplete, incorrect, or BOTH!! I have attached that schematic to this post. I have also tried several combinations of connecting these 10 wires together.... never have I gotten the truck's choke, choke heater and idling all to function properly at the same time, if EVER!!

The schematic shows that the power source wires for the Electric Choke are routed through the Oil Pressure Switch, and that that switch is actually a double switch, with one side not being used. The oil pressure switch on my totally stock Ram is NOT a double switch. It is a single pressure sending unit and the wires attached to it run inside the cab to the oil pressure gauge on the dash. I know this because when I disconnected the plug at that sending unit, the oil pressure gauge goes to zero.

The schematic further shows that the power for the Choke Heater comes out of the Electric Choke!! The choke is on the driver's side of the carb, and the heater is on the other side. My electric choke does have 2 wires on it; one goes into the big round barrel (solenoid) end, and the other is attached to a screw on the end of the kicker ram arm sticking out the other end. There's even a little hole with a grommet for the wire to go through to reach the end of that kicker arm. That arm makes contact with the throttle linkage (it pushes the linkage slightly in order to boost the idle during choke conditions). If there were power in that wire, it would (and DID) create a short to ground as soon as the arm makes contact with that linkage. The other 3 wires are (1) goes to the bowl vent which is easily found. the other 2 go INSIDE the carb body to the Oxygen Feedback Solenoid. This schematic shows 4 of the 5 wires should be DARK BLUE and one should be DARK GREEN. the schematic DOES NOT show that 6-way connector, so I went and traced the wires and found where a few of them went. BTW... on a cold engine, key on, 4 of the 5 wires have 12V and one has 0V. Because of the age of the truck, it is impossible to tell any difference in color of the 5 wires on the harness side of the connector; they're all black as far as anyone will ever be able to tell. However, at least 2 of them are 12ga wires, and the other 3 appear to be 14ga or 16ga.

Also... just before the Choke Heater, the wire that connects there goes to a little device which appears to be a thermal switch of sorts. It has about an inch anda half ceramic rectangular piece with fine wire leads running to either end of it, and a 14 or 16ga wire coming from a screw terminal on either end of the ceramic rectangle. This device is NOT SHOWN on the wiring schematic. I have no power on either side of that device... at least not with a cold engine. Those wires do not connect to the 6-way connector at the manifold. They disappear into the harness. What is the purpose of this little P.O.S device anyway?? And why can't I find where the wire feeding into it goes to??

SO...... I have put 1 hot wire to the dark wire going inside the carb to the Oxygen Feedback Solenoid, and the other from that solenoid to the one wire with no power at the connector. I traced it back to a DARK GREEN wire at the computer connector inside the fenderwell. I took another hot wire and run it to the Bowl Vent. That leaves 2 hot wires for the Electric Choke. When I did this and started the truck, the one wire to the end of the arm which is now in contact with the throttle linkage FRIED TO A CRISP. And I still have no power to the Choke Heater or to the little device just ahead of it. I traced all 5 wires and none of them go to that little device, yet the schematic shows it getting power from the back side of the Electric Choke Solenoid!! WHAT GIVES??

I guess I gotta find out which of the 4 cold motor hot wires still have power once the engine warms up?? I don't know how they would be able to change, since the schematic shows all the DARK BLUE wires are hot coming from the ignition switch and alternator and voltage regulator! They're all directly tied together. The only difference being the Oil Pressure Switch, which IS NOT in this loop on my truck! BTW.... how the HELL is Oil Pressure used to control a choke circuit?? I could see Oil TEMPERATURE being used.... but I don't get Oil Pressure's relationship to the choke circuit at all!! As soon as the engine fires, theres MAX oil pressure.... so that would turn the choke OFF?? And if, God forbid, you experienced a low oil pressure episode, then the electric choke would come on??? I don't gett it!!! Does the "Choke Heater" function like it sounds like it would; i.e. it gets hot when power is applied to it, thereby causing the spring to expand, pushing the choke arm upwards closing the butterfly on top to close? Or does the power make the spring retract the arm downwards thereby opening the choke for choke off conditions? And the Electric Choke (idle stepper solenoid)... does power applied to it make it kick the arm outwards, kicking the idle up? Or does power applied to it retract the arm, returning the idle to the curb idle screw? And why on Earth is there a wire attached to the end of it??

My truck runs, but without the choke working properly. Before I start it, I kick it open, and it'll catch on at least the first step of fast idle. But once running, as soon as you touch the throttle, it pulls off down to curb idle, so I gotta hold it up a li'l for a minute or two. I'm guessing its running in open loop all the time, which I've read on here means its on FULL enrichment all the time. Hence it's getting like 7 to 9 MPG max.

So I'm sure some of y'all have this wired up properly, and have the electric choke and choke heater both working as they should. Could you kindly take a look and maybe even probe your wiring harness to see how and where these wires need to be connected to operate properly? And could someone tell me WHY the wire is located on THE END OF THE choke kicker arm???? What kind ofa Moron designed THAT as a viable point to connect a wire?? I have been over this so many times I cannot even tell you, and I have GOT to get this thing ironed out NOW!! The truck has only 67,000 miles on the clock, and the tool boxes on the bedsides contain all my tools to support my family!

Thank you in advance, and thanks for reading all this drivel, and I'm awaiting your educated replies. ESPECIALLY those of you with this very set-up parked in your driveway!!

Mark D.

 

DAMN!!! I thought for sure I'd get some responses on this issue!! I have searched all through this forum and others for the answer to this wiring riddle... Can't find it written down anywhere!!

C'mon.... Somebody... with an '87 in their driveway?? Can you please just take a look at your connector at your manifold?? I'm certain that the harness-side wires have not been moved on my vehicle, so if you could just tell me which wires are connected to which pins on your truck, that might get mine to a better place. Once you disconnect the connector, hold the harness-side plug looking at the pins with the locking/guide tab on the bottom. Starting from Top Left, that's Pin#1, going clockwise around, winding up with Pin#6 directly below it. Now, re-connect the plug and follow the wires on the carb side to their destinations. One to the Bowl Vent, two to the solenoid INSIDE the carb, and then the other two wires. PLEASE?? I am begging you!!

Seriously, this will be a great help to me to at least get it into some kind of reasonable condition that I can use as a baseline.

Thank you in advance, and I'm awaiting your reply,

Mark D.

 

do you have 2 wires go to the idle up solenoid on left side of the carb? also trying to find out why my 87 d100 318 2bl run so bad