OP
BravoXray
Elite Member
- Joined
- Dec 17, 2019
- Messages
- 2,651
- Location
- Nothern Indiana
- Tractor
- Kubota BX2230, John Deere 430 Diesel
Okay, problem finally figured out and fixed. Fortunately, I guess, it wasn't my wiring error or something I did wrong.
After scanning the circuit diagram for the fuse block and bulkhead connector, I found a dashed line, the only one in all the wiring schematics, that was causing the problem backfeed.
Bear with me, I'll explain it. The accessory wire from the ignition switch goes to the fuse block to power a row of fuses that power accessory circuits. In the instrument cluster, one terminal of the the Generator light is connected to the normal ignition feed which powers the fuel gauge and other indicator lights, Water, Oil and Brake. The other terminal goes into the harness and into the bulkhead connector and then out in the underhood harness to the engine compartment, ending up next to the battery, but is not connected. However, for some reason the tech at American Auto Wire couldn't explain, there is a resistor wire connecting the accessory fuse bus to the generator wire. He couldn't explain why that was done, just that's the way they make them. The stock wire harness has no such connection, so I am at a loss for a reason they would do this, as it provides a direct path, albeit through a piece if resistor wire, between the accessory circuit and the normal ignition circuit. So, whenever the switch is in the accessory position current can feed from through that wire and the filament of the Generator light into the ignition circuit. Because of the resistor wire and the resistance of the Generator bulb, only a small amount of current can pass, just enough, around 2.5 to 3 volts, to make the MSD EFI display try to power up, fail and repeat the sequence every second or two making the screen flash on and off.
Once it figured this out, while the instrument cluster was out, with the ignition switch in the accessory position, on the cluster connector, I could connect the cluster power wire to the Generator light wire with a test light, and duplicate the problem.
To fix it properly, would mean pulling the fuse block out, finding the resistor wire and cutting it out, but, that would be a nightmare working under the dash and having to pull the brake mater cylinder and booster to get access to the nuts holding the fuse block and bulkhead to the firewall. So, instead, I figured out that putting a diode in the circuit between the Generator light and the bulkhead connector would prevent any current bleeding over from the accessory circuit. There is a short harness from the main dash harness to the instrument cluster, so I installed the diode in that harness. I used a 10amp Schottky diode, as they have a lower forward bias voltage, ~.2 volts, versus ~.6 volts on a normal diode. While at this point, the wire isn't being used, if I do ever decide to use it, it will have sufficient current carrying capability and very little voltage drop.
I got the dash completely reassembled this afternoon, and everything works as it should, finally.
Before I had pulled it apart this time, the fuel gauge had stopped working, which I traced to a break in the printed circuit overlay on the back of the cluster, so I replaced that. I bench tested the gauge and all the indicator and backlighting lights, and everything worked. I also checked the circuit going to the level sensor in the gas tank, and since the tank is full, it read about 90 ohms, which is correct. The gauge shows right on the full mark now.
So, after a year of trying to figure out the problem, I finally have it solved and understand what caused it.
That only leaves one problem I have left to resolve. At speeds over 65 mph, I have a driveline vibration. I can feel it in the shifter, and it's speed dependent, not RPM dependent, so it's either the driveshaft out of balance, or a driveline angle problem. Being that the driveshaft is new, I'm thinking it's an incorrect pinion angle causing it. When I was installing the differential and the driveshaft, I must have installed a wrong shim when I set the pinion angle. I'm going to check with my alignment shop to see if I can get it on their alignment rack so I can check the angles while the car is level. I'll update the thread when I get that sorted out.
Everyone stay safe and well.
The dashed line above the fure block and the bulkhead connector is the culprit.
Diode installed in the harness.
New printed circuit overlay.
After scanning the circuit diagram for the fuse block and bulkhead connector, I found a dashed line, the only one in all the wiring schematics, that was causing the problem backfeed.
Bear with me, I'll explain it. The accessory wire from the ignition switch goes to the fuse block to power a row of fuses that power accessory circuits. In the instrument cluster, one terminal of the the Generator light is connected to the normal ignition feed which powers the fuel gauge and other indicator lights, Water, Oil and Brake. The other terminal goes into the harness and into the bulkhead connector and then out in the underhood harness to the engine compartment, ending up next to the battery, but is not connected. However, for some reason the tech at American Auto Wire couldn't explain, there is a resistor wire connecting the accessory fuse bus to the generator wire. He couldn't explain why that was done, just that's the way they make them. The stock wire harness has no such connection, so I am at a loss for a reason they would do this, as it provides a direct path, albeit through a piece if resistor wire, between the accessory circuit and the normal ignition circuit. So, whenever the switch is in the accessory position current can feed from through that wire and the filament of the Generator light into the ignition circuit. Because of the resistor wire and the resistance of the Generator bulb, only a small amount of current can pass, just enough, around 2.5 to 3 volts, to make the MSD EFI display try to power up, fail and repeat the sequence every second or two making the screen flash on and off.
Once it figured this out, while the instrument cluster was out, with the ignition switch in the accessory position, on the cluster connector, I could connect the cluster power wire to the Generator light wire with a test light, and duplicate the problem.
To fix it properly, would mean pulling the fuse block out, finding the resistor wire and cutting it out, but, that would be a nightmare working under the dash and having to pull the brake mater cylinder and booster to get access to the nuts holding the fuse block and bulkhead to the firewall. So, instead, I figured out that putting a diode in the circuit between the Generator light and the bulkhead connector would prevent any current bleeding over from the accessory circuit. There is a short harness from the main dash harness to the instrument cluster, so I installed the diode in that harness. I used a 10amp Schottky diode, as they have a lower forward bias voltage, ~.2 volts, versus ~.6 volts on a normal diode. While at this point, the wire isn't being used, if I do ever decide to use it, it will have sufficient current carrying capability and very little voltage drop.
I got the dash completely reassembled this afternoon, and everything works as it should, finally.
Before I had pulled it apart this time, the fuel gauge had stopped working, which I traced to a break in the printed circuit overlay on the back of the cluster, so I replaced that. I bench tested the gauge and all the indicator and backlighting lights, and everything worked. I also checked the circuit going to the level sensor in the gas tank, and since the tank is full, it read about 90 ohms, which is correct. The gauge shows right on the full mark now.
So, after a year of trying to figure out the problem, I finally have it solved and understand what caused it.
That only leaves one problem I have left to resolve. At speeds over 65 mph, I have a driveline vibration. I can feel it in the shifter, and it's speed dependent, not RPM dependent, so it's either the driveshaft out of balance, or a driveline angle problem. Being that the driveshaft is new, I'm thinking it's an incorrect pinion angle causing it. When I was installing the differential and the driveshaft, I must have installed a wrong shim when I set the pinion angle. I'm going to check with my alignment shop to see if I can get it on their alignment rack so I can check the angles while the car is level. I'll update the thread when I get that sorted out.
Everyone stay safe and well.
The dashed line above the fure block and the bulkhead connector is the culprit.
Diode installed in the harness.
New printed circuit overlay.
