TheSamba.com :: View topic - Fuel Gauge interface Module for my ‘78 Bus

Wed Apr 30, 2025 6:45 am

I’m still chasing my fuel gauge issues….I have resigned myself to just taking a picture of the odometer and adding 200 miles. I was wandering around the web and found this:
https://www.tanksinc.com/index.cfm/page/ptype=product/product_id=748/mode=prod/prd748.htm

Has anyone else tried something like this? It looks very customizable, and can work with either known or unknown sender resistance by different calibration techniques.

I think I’m going to try it and I’ll report back

Eric

Wed Apr 30, 2025 7:01 am

you never posted back in your original thread what was going on. The stock gauge is pretty basic. They are not all that accurate anymore unless you calibrate them but they do work.

Wed Apr 30, 2025 7:30 am

My son and I tried installing a small resistor with a adjustment wheel in it, and the gauge never seemed to respond correctly…it would show full then quickly drop to almost empty after driving a bit and other times it would read differently without even driving. I tested the wire from the front to the back, and had good connection and continuity. I bought a few different senders and gauges, and we I tried different variations of them.

My son recently got a job at Raytheon, so his time with me is limited. I am just looking for a reliable solution that I can handle myself. I read thread after thread about resistors, Ohms, volts and the like, and know when I’m over my head. I can read a wiring diagram pretty well, and can usually handle most wiring but at this point, I just want a reliable fuel gauge. This unit seems to have multiple points of calibration so that should be good.

I’m hoping this is it.

Wed Apr 30, 2025 7:41 am

I had the same issue. A wire crimp was bad.

with the gauge connected, I would put a volt meter on the output of the voltage regulator and monitor it. The solid state style will give a steady voltage. The old b-metallic type will cycle on and off. Make sure that is consistent. I had a bad wire crimp at this location and it was turning the voltage on and off.

These are the components and places you can have issues.

Ground wire at sender
Sender
wire from sender to the a joint near the right rear
Wire from that joint forward to the gauge
voltage regulator for the gas sender
12V to that voltage regulator
wire between the regulator and gauge
wire from back that attaches to sender

Wed Apr 30, 2025 8:07 am

Thanks for the leads, I’ll go over them when I get home. I just want this to be reliable as I ran out of gas on Christmas Eve with the family onboard and it made for an interesting night.

Wed Apr 30, 2025 2:56 pm

Not having a gauge in the '59 beetle means writing down the milage and gallons added at every fill up.
With the bus gauge going to empty after maybe 40 miles of driving, I treat it like the bug and keep a notebook in the glove box with a pencil.
Calculating the mpg between fill ups also can give you a sense of where you stand tune up wise.

Wed Apr 30, 2025 3:40 pm

step 1. spin fuse #12 to improve contact. It should be an 8 amp fuse (white). Next time the fuel gauge drops, try your turn signals to see if they are working or not. The Hazard lights are also on this circuit and the top of the switch is known to come loose and cause some unusual issues.

If you eliminate that potential cause, Next step 2 is to check voltage at the gauge. If you have a plastic covered solid state gauge regulator, it should read I think around 5V as I recall. If you have the metal covered one, it has a bimetallic strip inside that turns on and off. In that case you will see 12V for a very short while, then zero until the strip cools, then 12V as it heats, then zero. There are contact points inside this version and they do corrode and wear out over hundreds of thousands of cycles. You would attach a wire with a ring terminal to (1) the output from the VR at the gauge and tape the end where you could hang it to get at it. (2) attach another wire with a double spade lug to the 12V hook up. The meter would get attached first between the Output from VR at the gauge and the other lead to ground. If the gauge fails to read, you would check for voltage on the other wire. If 12V is gone then you know the problem if a supply side issue. If 12V is there but no voltage gets to the gauge then you would know it is a VR problem. DO NOT LEAVE the power on to test things with the coil on the engine plugged in. That can damage the engine ignition and/or coil.

If the fuel gauge goes out and you have voltage present at the gauge where the VR supplies it, then you know the problem is on the sender side. if you are missing 12V then you will need to sleuth that but it is pretty easy.

Thu May 01, 2025 9:05 am

Thanks, it’s a very well description. I’ll start digging in.

Eric

Thu May 01, 2025 12:59 pm

That black box described in the first posting looks like it covers about all of the requirements for re-linearising an incorrectly constructed aftermarket float and arm type sender, or feeding a replacement gauge that is not off a Bay Window.