The Rodding Roundtable

Motorhead Message Central => Rodder's Roundtable => Topic started by: tomslik on November 18, 2023, 10:53:39 AM

Title: changing a 6V pos ground to 12V neg questions
Post by: tomslik on November 18, 2023, 10:53:39 AM
(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?
Title: Re: changing a 6V pos ground to 12V neg questions
Post by: kb426 on November 18, 2023, 01:18:49 PM
When I was young, people used a voltadrop resister to go from 12 to 6 volts. Outside of that, I'm no help. :)
Title: Re: changing a 6V pos ground to 12V neg questions
Post by: tomslik on November 18, 2023, 03:09:28 PM
yeah, did that. i suspect it has to do more with the polarity
Title: Re: changing a 6V pos ground to 12V neg questions
Post by: jaybee on November 18, 2023, 06:04:54 PM
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
Title: Re: changing a 6V pos ground to 12V neg questions
Post by: kb426 on November 18, 2023, 06:43:37 PM
I had a thought: could you connect a power window switch that reverses current and run it to the gauges through it?
Title: Re: changing a 6V pos ground to 12V neg questions
Post by: enjenjo on November 19, 2023, 01:06:49 AM
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.
Title: Re: changing a 6V pos ground to 12V neg questions
Post by: tomslik on November 19, 2023, 06:53:39 AM
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
Title: Re: changing a 6V pos ground to 12V neg questions
Post by: tomslik on November 19, 2023, 06:55:35 AM
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
Title: Re: changing a 6V pos ground to 12V neg questions
Post by: Crosley.In.AZ on November 19, 2023, 10:34:26 AM
If the sensor is not matched to the old gauge, will they work at all ?
Title: Re: changing a 6V pos ground to 12V neg questions
Post by: tomslik on November 19, 2023, 10:39:42 AM
it should be, it's all new for the truck (lmc)
Title: Re: changing a 6V pos ground to 12V neg questions
Post by: kb426 on November 19, 2023, 01:36:32 PM
Just for a test, how about connecting a 6 volt battery charger to them and see what happens?
Title: Re: changing a 6V pos ground to 12V neg questions
Post by: tomslik on November 19, 2023, 03:08:43 PM
enjenjo, how did you reverse the polarity.?
Title: Re: changing a 6V pos ground to 12V neg questions
Post by: enjenjo on November 20, 2023, 01:36:15 AM
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.
Title: Re: changing a 6V pos ground to 12V neg questions
Post by: tomslik on November 20, 2023, 07:01:40 AM
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?
Title: Re: changing a 6V pos ground to 12V neg questions
Post by: enjenjo on November 21, 2023, 12:12:54 PM
 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.