Guages Not Working

[TN78FJ40]

Hello IH8MUD, this is my first post but have been reading for some time now. I bought a 78 40 a couple of years ago and I am finally getting aroung to building it into what I want(will post some pics for the picture whores like myself as soon as I fix my bezel). My question today is that three of my gauges(gas,temp,oil) quit working all at one which sounds like a ground to me but wondering if someone knew how I might check this or where to look? Any ideas would be appreciated.

 

[grant5127]

Welcome!

checked the fuse?

 

[TN78FJ40]

Have checked all fuses under dash and they were all fine.

 

[bikersmurf]

Wiring harness ground.

One ground to check is to the inside of the Right hand fame rail below the passenger seat. I believe it is a white wire with a black line on it and it comes out of the wiring harness and attaches to the frame. I've seen weird things happen with the wipers and gauges when its not connected.


I don't know if it is the source of your problem but that's where I'd look.

 

[Pin_Head]

The gauges have 3 separate grounds, so it is not likely a ground problem.

If the fuse is good, then it is most likely a problem with the voltage regulator that is built into the gas gauge in the dash. Make sure that it isn't broken and the contacts are clean. If it is broken, you can bypass it, but the needles will fluctuate with the system voltage.

 

[TN78FJ40]

Was able to get gauges somewhat working. the fuse was fine but I was not getting power to the back of cluster so I ran new wire from same fuse to back of the cluster. Now the fuel and temp are working but the oil gauge is pegging out. Removed wire from oil sending unit and I am getting 11-12 volts from the wire with voltmeter grounded to negative side of batt. should I be getting that?

 

[Pin_Head]

If the OP gauge is pegged to the right, the wire or sender is shorted. If it is pegged left (eg never moves) then the wire or sender is open. Yes, you should have 11-12 V at the end of the wire when it is disconnected from the sender. If the gauge is not pegged right with the wire disconnected at the sender, then chances are the sender is shorted.

 

[Gusb]

My 78 FJ40 was stored for a long time, in what must have been a very damp environment. When I got it moving for the first time the gauges were working. Then a few days later they stopped working. I looked at the fuses and they just powdered-apart in my fingers. Replaced all the fuses with new and things were still not right. Finally checked the fuse block itself (meter) and found 1/2 the fuse contacts were corroded over and dead. Pulled the fuse block and cleaned everything up, rechecked the contacts/fuses and gauges, etc. have worked fine since. Most of my electrical seems original and every time I've had a problem it seems to be something like a grounded surface or other contact that just needs to be cleaned up. Just a thought.

 

[TN78FJ40]

Thanks for the responses. The OP gauge is pegged to the right but stays pegged even with the wire disconnected from the sending unit. Would it hurt to run a new wire from the unit staight to the cluster or are there any relays or regulators I need to to run to first? And Gusb, I did check my fuse box with meter and noticed they did need a good cleaning, they might not be giving me fits yet but they probably will. Thanks for the tip.

(If it sounds like I am dumb about this stuff its probably because I am)