F-350 Upfitter switch troubleshooting help plz

[skegpro]

Head scratcher here.

So slip tank pump stopped working.

Got home checked the 30 amp fuse on aux switch 4. All good.

Pulled the connector off at the pump turned on the aux switch, 14V. WTF

Take booster cables from the battery right to the pump side of the connector. Pump Works. WTF.

Cut the connector out and use marrettes to make the connection.
Turn on Aux 4, nothing.

Check the voltage on each marrette to ground, no voltage.

Turn the switch off on the pump, and have then voltage back on the positive wire, as expected. Wtf.

What am I missing here.
Worked for years like this..

 

[2kDoo]

try aux 3 ?

 

[skegpro]

try aux 3 ?

I have a light bar on aux 1 that works still....

But I could try moving it.

 

[skegpro]

............

 

[2kDoo]

as brutal as it sounds, reading what you posted I would try moving the aux, perhaps, just maybe the actual aux4 is somehow malfunctioned

 

[Tchetek]

Sounds like a Bad connection somewhere can’t handle the load.

When you tested with the booster cables did you just use the one positive cable and the trucks wiring for negative to rule out a bad ground issue?

 

[skegpro]

Sounds like a Bad connection somewhere can’t handle the load.

When you tested with the booster cables did you just use the one positive cable and the trucks wiring for negative to rule out a bad ground issue?

Yeah thats what I am thinking, broken wire or bad connection.

No I didn't try that, good idea. Will give that a go.

 

[skegpro]

Sounds like a Bad connection somewhere can’t handle the load.

When you tested with the booster cables did you just use the one positive cable and the trucks wiring for negative to rule out a bad ground issue?

Ok wiring is good.
Has to be something with the relay.

 

[skegpro]

Aux 4 is showing 14v but won't make the test light, light up.
Something fishy.

 

[Dawizman]

Aux 4 is showing 14v but won't make the test light, light up.
Something fishy.

Bad connection, not passing any current, but showing voltage with no load. Probably a bad relay.

 

[Dooitorbust]

Bad relay is good start, and usually fairly simple to do. Like others hat said, it’s probably a corroded, or broken wire somewhere. Sounds like there is just enough good strands to read voltage, but as soon as a load is out on it, it can’t handle it and cuts out.
Chasing wiring can be frustrating. Worst one I found was a broken wire inside a harness, but it wasn’t visibly broken on the outside. When I gave each wire a tug test, you could see the wire casing stretch, as the strands were broken inside a single wire.
A good multimeter is your friend.

 

[skegpro]

Man did Ford bury these relays.

So Aux 4 and 3 look to be a 20 amp relay, pump is 19.8amps lol.

aux 1and 2 look to have 50 amp relays.

Will try moving some stuff around.

 

[Cdnfireman]

Sounds like a burned/corroded relay contact. Try swapping relays in the upfitter relay box under the hood and see what happens. If that doesn’t cure it, I’d be looking at the grounding for the pump.