New trailer tongue weight scale

The last few times I've needed to weigh a trailer tongue, for load balancing, I used the old simple beam/bathroom scale trick. But that gets annoying, dragging out concrete blocks and a 2x4, the calculating the sum of moment to get the scale factor.

So I started shopping around for a tongue weight scale on Amazon, and wasn't really liking the spring contraptions available. Except the Hydraulic Sherline LM1000. That thing looks pretty nice, but also $$$.

Then I spotted a few chunks of scrap out in the shop, from old projects, years ago, and decided to try and make one.

I already had everything needed on-hand, except the 1000 psi pressure gauge, which was 9$ on Amazon.


I turned the body from a chunk of 3" 6061-t6 rod and the 1.128" (so it would have a face area of 1 square inch), dia hydraulic piston from a piece of 1.5" 4130 chromoly rod. I used my parting tool and added two o-ring grooves, then milled a small slot for a retaining dog point screw.





The dog point set screw will keep the piston from slipping out, if someone picks it up by the piston.


I got it all assembled and filled with AW 32 hydraulic oil.

With a 1 SQ inch piston and a 1000psi pressure gauge, the weight to pressure ratio will be 1:1, so a reading of 500psi means 500lbs of weight.




I tested it by standing on it. It showed my weight perfectly.


So, my cargo trailer weighs 2500lbs empty. The tongue shows 270'ish lbs. 11% of it's weight on the tongue.

And, no leaks! I'm happy with the way it turned out, even if it does look like some kinda gothic steampunk sex toy.







I'm in it for the Amazon 9$ gauge, 2 hours of time, about 25cc of oil about 20$ worth of metal leftovers.

Ken226 said:

I'm happy with the way it turned out, even if it does look like some kinda gothic steampunk sex toy.

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Best line I've heard in a while.

Great job on design and implementation.

One could go with a Weight Safe hitch with the built-in scale.

BossHogg said:

One could go with a Weight Safe hitch with the built-in scale.

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Yes, those are nice. Very nice. Unfortunately it won't work with uHaul's welded on 2" ball. Also, their trucks that have a 2" receiver, have it mounted directly above the bumper, so alot of hitches with more than 4" of drop won't work, unless the 2" square part is extended pretty long.





It would be perfect for ones own truck though.
It's pretty pricey though. Definitely more than 9$

I bought their clamshell 2" to 2-5/16" ball adapter. Despite looking kinda sketchy, I used it for about a week and it works great

Uhaul trucks have a 2" ball permanently welded on, so if your trailer has a 2-5/16 coupler, options can be limited

My father was a tool and die maker, and would make things like that for me. I miss him.

incredible work there

The new trailer didn't come with clearance lights.

Last week I was trying to find the right wires for the tail/running lights, to splice into.

Backing up to the trailer and connecting the truck, for power, so I can probe for the correct wire would leave my truck blocking the road. I decided to use my Noco jumper box and some alligator clips, attached to small screwdrivers, which were jammed into the connector to provide power to the tail light circuit. A little bit sketchy.

It was kinda annoying, so I got some ideas for a permanent solution. I saw these things on Amazon for 164$. I decided to see how cheap I could make one. But, I wanted mine to run on DeWalt batteries:



A DeWalt adapter with 20v to 12v buck converter. $23.74:

I needed a RF transceiver relay controller, with 4 relays. $18.99:

2 Schottky diodes, to prevent the turn signal current from backfeeding into the brake light circuit and lighting both turn signals, when only one turn signal is activated. $6.52:

A SPST illuminated toggle switch. I wanted to control the tail lights/running lights with a switch. The brake, reverse and turn signals to be controlled with the remote fobs. $5.99:

A combo 7 pin/4 pin female trailer connecter. I thought it would be cool to be able to use it on either/or. $25.49:

Wire. $14.99:

A terminal kit. $5.99:

A bunch of screws. $12.99:


I 3d printed the box, wired it all together, then spent an hour trying to figure out why it didn't work right. I finally discovered that the Chinglish manual for the RF transceiver board was wrong, and swapped the NO and NC terminals on the relays.

After that, it worked perfectly.



On the remote fobs, button A is the brake lights, button b is the reverse lights, C and D control the left and right turn signals, respectively. But, they can be wired or rewired any way one wants. Mine is set to run the fob buttons as momentary, but the board also allows for the buttons to be set to toggle.

And yea, I already know, testing the left and right signals automatically verifies the brake lights, because most trailers use the same circuit. But, then i'd have an unused relay on the board, and for some reason I had an odd compulsion to not leave one empty.








All in, the cost was $114.70 and about 2 hours of labor.


It would have been less than an hour except for the Chinglish manual swapping the NC and NO terminals.

It's way more convenient now. I can connect a DeWalt battery, plug in the trailer and have Aux power to run the interior lights. I can toggle on the running lights and tail lights, and remotely verify the reverse lights, brake lights and L/R turn signals.


I guess all in all, if you include labor, the one on Amazon isn't such a bad deal.

Nice work, a lot to be said for doing it yourself rather then just buying something.

I'd forgot. A little out of order, but I made these dewalt powered work lights back around the beginning of the year. Used some of the same electronics as the trailer test box.

I made 2 of them, 3d printed.