Wire Gauge For Fuel Tank Sender - Does Splice Gauge Matter? (1 Viewer)

[cdubatl]

Hi All. I've had my '76 40 since February and the gas gauge has never worked. Been ticking through a list and started tracing wires since I'm waiting on parts. I replaced the sender this week even though it tested right with 3ohms resistance. Connections in the dash look tight and I pulled it out of the speedometer cluster and sprayed everything with electrical contact cleaner. Started tracing the wires looking for issues and came across a splice in the engine compartment.

The wire is yellow with the red stripe. It is spliced in two spots with a larger gauge wire. One just above the rear harness connector and the other just before it enters the firewall. It is probably the easiest place for it to be in terms of access. Since it isn't working I will obviously cut out the splice and re-wire with waterproof connectors.

My question is does the gauge matter? It looks like the splice wire is a larger gauge. Would that be enough to make the readings not work? If yes, is the correct gauge 18? I've always thought of always ok to go larger on wire gauge but maybe not for a sender?

Photo of the splice below:

Thank you.

 

[pithicus]

I doubt the miniscule change in the resistance from a different wire gauge would make any difference in that sender circuit

 

[cdubatl]

I doubt the miniscule change in the resistance from a different wire gauge would make any difference in that sender circuit

Awesome, thanks.

 

[ToyotaMatt]

Awesome, thanks.

Larger Guage OK ..........

Smaller Gauge NOT-OK

do you have a dedicated stand alone ground =RING Terminal on one of the sender screws ?

that helps MUCH with any resistance values as well , and proper sender function

 

[JVZii]

One thing to check is the board on the back of the cluster. It it was ever taken out with the battery connected the legs on the circuit board can burn.

It would look kind of like this but on the fuel leg.

Do you have continuity from the gauge plug to the sending unit plug? If so then that shouldn't be the problem.

 

[B y r o n]

With regard to the resistance in different size wires I found this: "Smaller wires always have greater resistance than larger ones. This is because there is less room for current to flow through. Current is simply the flow of electrons. When a wire is smaller, the electrons have less room to go through the wire."

 

[73FJ40]

I would be more concerned with resistance in the splice connectors, and corrosion on the dedicated ground wire running from the sending unit to the frame.

 

[cdubatl]

Thanks. Yes, it has a dedicated ring connector to one of the sender screws. Cleaned it off with contact cleaner and a wire pad just to make certain it is all good. Still no signal to the cluster so working my way up the harness and back through the dash.

I didn't see any burned or broken wires on the circuit board but will go back and look when I pull it out again.

 

[73FJ40]

@cdubatl

Thanks. Yes, it has a dedicated ring connector to one of the sender screws. Cleaned it off with contact cleaner and a wire pad just to make certain it is all good. Still no signal to the cluster so working my way up the harness and back through the dash.

I didn't see any burned or broken wires on the circuit board but will go back and look when I pull it out again.

"on the dedicated ground wire running from the sending unit to the frame.

There are two ends to the ground wire. You cleaned the one, inside the cab, protected from the elements, and not the one, under a steel screw, fastened to the frame, right above where the skid plate collects and stores all the mud and yuck.

 

[73FJ40]

@cdubatl

This picture illustrates the ground wire for the sending unit on my '73 FJ40. Your '76 may be different.

You can see at the left of the clip holding the brake line and wire harness the branch circuit going over to the fuel tank. the ground wire white/black trace, comes out of the harness and attaches to the frame rail under the screw and clip.

Not a great place to maintain a good ground for a device that relies on resistance for accuracy...

 

[middlecalf]

Electrons (-) flow on the surface of the wire/wires from negative terminal to positive terminal. Greater diameter = greater surface area.

 

[cdubatl]

Wow - that is cruel to hide it there. Confirmed that the ground screw to frame is in the same place on a 1/76. I've got a feeling this will require some scrubbing. Will update in the morning. I love mud!