40 Years Later - The Re-build

This is not a direct answer to your question, but the painless performance sending unit wire (#939) is 18ga.

 

The wire size and length will have a little effect on the gauge. The sending unit can be "calibrated" by bending the arm with the
tank empty to get the lowest reading. That said, these are not perfectly accurate and will require some interpolation to see where
the tank is full or empty. Two tanks are a nice thing to have or a spare gas can.

 

Yep, the only current in that wire is that resulting from the resistance of the sender and is very low. You would have to use some rather tiny wire to make any difference. As noted above, bend the float wire to adjust.

 

Thanks everyone. I was going to start bending the float arm around a bit but didnt want to do that without consulting the experts first!

 

So I did a little more testing before I'm bend anything. I made new connections on the wires so they're extra fresh, too.

With the sending unit out of the tank, no send/ground wires connected here are my Ohm readings:

Float Lowest Point/Empty: 79 ohms
Float Highest Point/Full: 9 ohms

With the wires attached to the sending unit, ignition off:
Float Lowest Point/Empty: 30 ohms
Float Highest Point/Full: 8 ohms

Sender & ground connected, ignition on, float at highest point only shows 1/2 tank reading on gauge.

Any thoughts? Why would it show less resistance with the sending unit wire attached?

 

I would imagine there is some leakage to ground via the gauge itself of the power supply that feeds the gauge. That would confound the result the multimeter is calculating. You need to measure resistances in isolation.

The sender seems to be in the right range. You can check the power supply and the gauge itself with info from this page: https://www.extremeterrain.com/cj-gauge-troubleshooting-tech-guide.html

 

Pulled the speedo out and swapped out the fuel gauge for another gauge we had laying around. Same part number but slightly different fit, Steward Warner must have changed some things. Now it's shorting out on the housing and popping the fuse. Going to have to pull it out and figure something else out.

Here's a photo of the back of the gauge we pulled out. I dont have a pic of the one we replaced it with. Stud position was slightly different, but still fit.

 

So I pulled the speedometer out again. You can see the differences in the gauges in this photo. The original from 1958 is on the right, and the one I swapped it with ( i think 1970) is on the left. You can see the difference in the stud position when I overlay the cardboard isolators. My thought is that the studs are contacting the speedometer housing and causing a short.

 

Got it working with the later gauge and regulator. Still showing empty @ half tank, and just above half if I move the float to full. So back to MTS the sender goes!

 

Saga continues. The 1st sender went back to MTS for testing. Checked out fine. I still bought a second one anyway. Installed the second one and it’s acting the same way. Ohm reading is within range, drop it in the tank (half full) shows empty on the gauge. Manually raise the float to the top of the tank with a stick and it reads slightly above 1/2 tank. Not sure what else could be doing on. Project for another time I guess.

 

Checked mine with ignition off and tank close to full...0-Ohms. It reads 6 Ohms when disconnected. A spare I have reads 76-78 empty and not connected and 4.6 Ohms full.
The voltage regulator is supposed to put out 5-7 volts. This is a pulsating DC voltage and would probably require an analog meter to read it, such as a Simpson 260. Hope
this helps. John

 

Still not quite road ready, but we got our tree today and it was warm so I couldn’t help but pull the 5 out for a few photos. Had the chance to drive it around the block. Really looking forward to taking it for a longer ride one of these days.

happy holidays

 

That is nice.

 

Nice!

 

Took the 5 out last night for the first "long" ride, about 30 minutes. Ambient temp was ~40*F but the engine came up to operating temperature great, both heaters were blowin' nice. All the gears are working, the overdrive module too. I don't have the transmission cover installed yet, so its pretty noisy. My dad thinks that may be because the T90 was full of water at some point. Will have to see how it goes after a few fluid changes. Still need to adjust the brakes as it pulls to the right when braking. Overall I'm very happy with how its running and driving. I still have a huge smile on my face. I'm going to try and get the passenger seat installed this weekend so I can take my father for a ride. It will be his first time in the Jeep under its own power since the accident in the early 80's.

I have a questions about the alternator: When I start the engine the AMP light is lit, until I get up to about 2,500RPM when it goes out and it starts charging the system. Is that common for the 10SI units?

 

That is pretty normal. If mine idles long enough, it will go out and start charging on it's own. I believe it is because there is not enough resistance[load] from the
bulb alone to excite the alternator sooner.

 

Got it, thank you. It was pretty fun watching the headlights get brighter once the alternator kicked in!

 

I really don't mind it taking longer as it is a reminder to check all gauges, e-brake, etc. for take-off procedure.

 

Mr Roger’s had indoor and out door shoes too. lol

 

Took it for a ride to the beach.