Fuel Gauge Wiring - Help Verify (1 Viewer)

[NikP]

I'm installing autometer gauges in my cluster to replace amp, temp, and oil stock gauges.

I'm keeping my fuel gauge but in doing this I've build a new enclosure for my gauges and not using the factory circuit board.

Can someone help validate the terminals on the fuel gauge so I don't ruin it when I plug it in? I'm pretty sure the following diagram is correct but want a second opinion.

Thanks.

 

[lostmarbles]

I think the top one is 12V but that it gets it internally somehow?. Edit: Wrong! (See amaurer's post #6 here) It is a stepped-down voltage output from the fuel gauge so leave it UNCONNECTED NikP

(There's no external connection to it anyways.)





Edit : The above photo shows a 1980's BJ42 combination meter. And there the top terminal appears to be linked (via the printed circuit board) to the coolant temperature gauge. And the OTHER terminal of that gauge goes to the temperature sender. That's why I'm assuming the top terminal gets 12V. (Because the side of the temperature gauge it is connected to must surely be getting 12V somehow internally?). But whether it gets 12V only when the ignition is turned on (via the LR wire on the round plug) or whether it gets it permanently via one of the ammeter feeds (white connector) ...... well .....I dunno. Anybody able to help. (Coolerman/Mark?)

 

[bsmith123]

gauge

I realized you said circuit board and some of the pics are the old style pre 72 but in the links there are pics of the circuit board type

the 12 V that is ignition switched should be your power in, the other wire to the sender
So from Lost marbles post I would assume the bottom left would be your power hook up

On mine the early fuel gauge has a regulator for power to the other gauges, in the later schematics it just appears to have all the gauges in parallel for power

Can anyone pipe in on that? do the later gauges self regulate or do they still get power from the fuel gauge or other regulator?

the wires could be figured out by putting an ohmeter on it and then pulling the wires at the sender, to the other gauges, and to the fuse one at a time, the fused power will prolly read open through the ingition switch and the other 2 have resistance on them until you pull the wire then go open

http://www.globalsoftware-inc.com/coolerman/fj40/schematics/FJ40/1975FJ40/Haynes1975FJ40Page1.jpg

http://www.globalsoftware-inc.com/coolerman/fj40/schematics/FJ40/1981FJ40/Haynes1981FJ40Page1.jpg
not sure what year you are but there are numerous schematics on Coolermans Website for wiring

https://forum.ih8mud.com/40-55-series-tech/370223-guage-clusters-differences.html

https://forum.ih8mud.com/40-55-series-tech/279131-electrical-help-911-a.html
*post number 12 in this link


https://forum.ih8mud.com/40-55-series-tech/407021-fuel-gauge-sending-unit.html

FJ40 DIGITAL INSTRUMENT PANEL - Teltek U.S.A INC.

 

[Pin_Head]

There isn't much to it. There is the + side and the sender side. If you reverse the leads, the meter will just swing the wrong way.

 

[lostmarbles]

There isn't much to it. There is the + side and the sender side. If you reverse the leads, the meter will just swing the wrong way.

So what's your enterpretation on this terminal then Charlie:





As Kikp says as the beginning .... he has 3 terminals on his fuel gauge

 

[amaurer]

From the rear:

Left - 12V ignition +
Middle - ~7V regulated output for other gauges
Right - fuel tank sender

There is also a grounding "tab" on the gauge which is pressing onto a pad on the other side of the board. If you're running the gauge dismounted from the circuit board you'll need to make sure to ground said tab.

There isn't much to it. There is the + side and the sender side. If you reverse the leads, the meter will just swing the wrong way.

Not on this gauge, it can only swing one way (it works on heat, not on magnetism).

 

[lostmarbles]

...
Middle - ~7V regulated output for other gauges

Thanks Drew.

And in the case of the BJ42 combination meter I photographed(and my BJ40 meter too I believe) the only gauge that needs this "lower 7V regulated voltage" is the coolant temperature gauge.

(The ammeter doesn't need any "operating voltage" and the oil pressure gauge uses 12V.)

Interesting! (I love learning stuff like this.)

 

[LocoJR]

I thought I should repost this for those that have more info than me to confirm, and those floundering with FJ40 gauge problems.

================
This seems to be a common thread to gauge problems. The 7v regulator seems to be a wire resistor around a bimetal strip in the fuel gauge. Mine ('74 FJ40) appears to have a break-contact if it draws too much current and heats.

This is besides the bimetal for the actual fuel gauge. If there is a short in the fuel or temp, or the circuits, it would cause an intermittent problem when the 7v regulator bimetal heats up.

Can somebody confirm?

 

[LocoJR]

My mistake. The regulator should buzz if it's operating correctly, averaging 7v using duty cycle. Look up Smiths Voltage Stabilizer.

JR