Rotten

I was helping my friend change the fuel filter in is 1990 W250, when all of a sudden, I see white smoke coming from the injection pump area, and from the grid heater relay area. The truck was running, and I saw two Little wispy trails of smoke like a match being lit, not exhaust smoke or anything. One from the injection pump area, and one from NEAR, but not FROM the grid heater relays. I'm on the passenger side, about 6 feet away, and before I can tell him to cut it off, the truck dies. Try to recrank, and nothing, no clicks, no nothing. Plus the dash lights quit working. We checked all the fuses, none were blown that we could tell.

Clearly some sort of short happened, and it killed the starter or ignition relay, and the fuel cutoff solenoid relay as well? Any advice on where to start troubleshooting? Plus, he dropped his cell phone in between the radiator and AC condenser So we have to pull the radiator tomorrow as well.

dieselJon

Fusible links. 1 wire going in on the battery side, about 4 coming out on the cab side. Look right between the grid heater solenoids and the driver side fender.

Rotten

Fusible link is still good. There is power to the starter, but it still won't turn over, and there is no power to the fuel solenoid on the pump. I'm guessing now that it has some issue with the ignition/key?

NE frmhnd

Mine blew a link, I had headlights but nothing else. Wouldn't click the starter or anything. I tried sticking probes from a DVM into the fusible links but they showed power on both sides. Ended up running a couple 12 ga wires into the cab and making jumpers to go from the ignition switch to its plug, and ran the 2 powered wires into that. Been on it for 2 years now. Lift the wiring harness up from on top of the brake booster, that is where mine shorted, couldn't see it until I ran on some really rough roads one day, but it did wear through on the flat metal in there.

j_martin

The power you speak of goes through a fusible link just aft the battery, then the ignition switch, then all over heck on a dark blue wire (fuel shutoff solenoid, OD solenoid, etc.) (A21 circuit)

The wiff of smoke you saw was from the fusible link. It is inside a fireproof sleeve so you have to find it with a meter. It is the one connected to 12G red wire.

torquefan

There are several fusible links all together. Usually the conductor will melt and break, while the insulation still looks perfect. Give each one a little tug. The bad one will be all stretchy.