K75 fuel pump fuse blowing...

[Skippy]

I’ve got a problem with my 1995 K75.

My fuel pump fuse is blowing when I hit the starter. The starter runs and engine turns over but it doesn’t start. If I don’t hit the starter, the fuse is fine, but blows immediately (or shortly after) the starter is pressed.

I have tried unplugging the lead going to the tank (fuel gauge and fuel pump), and the fuse remains ok when I hit the starter, but of course the engine doesn’t start as the fuel pump is unplugged. I have tried unplugging the gear box switch (electrically upstream of the fuel pump) and the fuse remains ok when I hit the starter, but the engine doesn’t start and I can’t hear the fuel pump running.

 

Has anyone experienced something like this before?

Does this mean my fuel pump is shot? How can I test it?

Am I barking up the wrong tree?

 

Any help will be appreciated...

[JerryMather]

Get a meter on the fuel pump connection and the frame to see if the circuit is grounded. If it's not, the meter will show nothing. If the meter display moves, it's grounded and the pump will need to be replaced or the wiring will need to be checked for shorts.

Check all the connections one at a time to trace out the problem area.

[Skippy]

Ok there are four wires in the tank connection on the K75:

 

Green / White Stripe (G) - goes to the fuse panel

Brown (B) - goes to the gear box switch then to the gear indicator and a bunch of other stuff

White (W) - goes to the fuel indicator light

Yellow (Y) - goes to something that Clymer calls the "Plug Connection, Additional Instruments"

 

I opened the tank connection and took some resistance readings across the wires:

 

Harness side to Ground

G - 250 ohms

B - 0 ohms

W - 2M ohms

Y - /

 

Harness side to battery (+)

G - 0 ohms

B - 0 ohms

W - 0 ohms

Y - /

 

Tank side to Ground

G - 2M ohms

B - 2M ohms

W - /

Y - 2M ohms

 

Tank side:

G - B - 2 ohms

G - W - /

G - Y - 2M ohms

B - W - /

B - Y - 2M ohms

W - Y - /

 

My suspicion is that the fuel pump if powered between the Green / White Stripe (+) and Brown (-) wires. Should the fuel pump present more then a 2 ohms impedance?

[kioolt]

I wouldn't trust any of your readings on the harness side if you didn't unhook the battery. An ohmmeter will not give correct readings if there is any voltage on the circuit being tested. Even voltage as little as a few milivolts with make the readings meaningless.

[Skippy]

Got it.

Ok I unhooked the battery and re-read the resistance readings.

 

Green / White Stripe (G) - goes to the fuse panel

Brown (B) - goes to the gear box switch then to the gear indicator and a bunch of other stuff

White (W) - goes to the fuel indicator light

Yellow (Y) - goes to something that Clymer calls the "Plug Connection, Additional Instruments"

 

Harness side to Ground

G - 250 ohms

B - 0 ohms

W - 1M ohms

Y - /

 

Harness side to battery (+)

G - 150K ohms

B - 150K ohms

W - 1M ohms

Y - /

 

Tank side to Ground

G - 2M ohms

B - 2M ohms

W - /

Y - 2M ohms

 

Tank side:

G - B - 2 ohms

G - W - /

G - Y - 1M ohms

B - W - /

B - Y - 1M ohms

W - Y - /

 

Does any of that look problematic?