changing a 6V pos ground to 12V neg questions

[tomslik]

(51 F-3 ford) painless wiring, stock gauges.
it occurred to me last night that this could be an issue. has anybody successfully made the gauges work?
new temp sender reads hot, oil reads 0, fuel gauge reads F and it's not.
new tank and sender, new temp sender, oil is original....ideas?

[kb426]

When I was young, people used a voltadrop resister to go from 12 to 6 volts. Outside of that, I'm no help.

[tomslik]

yeah, did that. i suspect it has to do more with the polarity

[jaybee]

Can you swap the connections on the gauges or senders? What sort of voltage drop resistor are you using? One of these might work:

https://www.napaonline.com/en/p/MPEVT6187SB
https://www.tractorsupply.com/tsc/product/ford-electric-resistors-2300896?store=1732&cid=Shopping-Google-Local_Feed&utm_medium=Google&utm_source=Shopping&utm_campaign=&utm_content=Local_Feed&gad_source=1&gclid=Cj0KCQiA3uGqBhDdARIsAFeJ5r2KnHDw1roimvh2KCKPzC49gf93Ky3sfBB8f7JY3Y6qA7Ap9UtgjckaAmbgEALw_wcB

[kb426]

I had a thought: could you connect a power window switch that reverses current and run it to the gauges through it?

[enjenjo]

On my 52, same gauges, I just reversed the polarity, and installed a 56 Ford instrument voltage regulator in line. I made no other changes. It never was a problem. The only thing I had a volt-a-drop on was the electric wipers.

[tomslik]

i'm using one of these,https://www.lmctruck.com/1948-56-fords/wiring-components/fa-1948-56-voltage-reducers
i'm wondering if i should be using 3 of them though

[tomslik]

i'm using one of these,https://www.lmctruck.com/1948-56-fords/wiring-components/fa-1948-56-voltage-reducers( the electronic one)
i'm wondering if i should be using 3 of them though

[Crosley.In.AZ]

If the sensor is not matched to the old gauge, will they work at all ?

[tomslik]

it should be, it's all new for the truck (lmc)

[kb426]

Just for a test, how about connecting a 6 volt battery charger to them and see what happens?

[tomslik]

enjenjo, how did you reverse the polarity.?

[enjenjo]

Positive to the gauge power, negative to the ground. if you are using a generator you have to re-polarize the generator, and use a 12 volt regulator. I had an alternator on mine.

[tomslik]

i've changed it to a gm alt (speedway bracket), tried isolating the gauges from the housing and going positive ground (might've killed a gauge or 2...)
could it be that the bigger trucks were already negative ground?

[enjenjo]

 I used one of these  https://www.dennis-carpenter.com/bronco/electrical/battery/b9mz-10804-c-instrument-cluster-voltage-reg  and wired the gauges as stock , just reversing the polarity. I have done this on various Fords and it has worked every time. You can use a 0 to 200 Ohm potentiometer to test the gauges out of the truck. If you reverse the power and sender terminals on the gauge you can damage the movement.

The big trucks were positive ground until they switched to 12 volts.