Gauge Issues

[dmack91]

I am having trouble getting my gauges to work. The only things that are working are the oil pressure and temp. gauges (surprisingly, they are controlled by their own inputs independent of the cluster).

My speedo doesn't work (I assume it is the cable, so I'm not really concerned with that at this time).

The gas gauge is stuck on 3 o'clock, past full. Turn signal indicators and dash lights don't work. I grounded the gas gauge terminal on the fuse panel per Vettevet's instructions, and it went to empty, so the gauge should be fine.

I have run a jumper wire from the neg battery terminal to the dash light with the black wire clip coming off of the back, and to a couple of the mounting hex screws on the back of the cluster, but still no luck.

I have heard of grounding the gas gauge terminal, but don't know which one and don't want to take the chance of smoking something just for the sake of trying anything.

Any suggestions would be greatly appreciated.

Thanks

[BearFlagRepublic]

Well I can't help you with everything but I will do what I can and know (from experience) to try. On the gas gauge issue it sounds like there's likely an issue with the sending unit not the gauge itself. I would check the float first as they will generally corrode and allow fuel in, causing them not to float, You can also check the sending unit (not just float) at that point by moving the lever up and down to see if the gauge moves. This will tell you if you just need a float (easy to get at LMC.)

The Speedometer likely is an issue with the gear in the trans itself not the gauge, it could be the cable though like you said. The easiest way to check is to take the cable out from the trans and manually turn it or turn it with a drill. this will let you know if it's the cable, or the gearing inside the trans, both are fairly easily fixed.

[Longhorn Man]

if the fuel guage is reading past full, I highly doubt it's from a float that sank to the bottom. That would read empty. Pull the seat forward and see if the tan wire is hooked to the sending unit. If it is, then remove the chrome/rust colored door sill plate on the drivers side and inspect that same tan wire. It's probably corroded and split in two in this location. If it's good, follow it north to see if it is broken further up, or not plugged into the fuse block.
More possibilities, but this is the most likely issue.

[dmack91]

Thanks. I have checked the wire from the sending unit to the fuse box and it tests good.

From what I have read on other threads, I was thinking a grounding issue since the dash lights don't work either. Unfortunately, I have tried grounding it in several places on the cluster to the battery without success.

Thanks again for the suggestions.

[VetteVet]

Originally Posted by dmack91

I am having trouble getting my gauges to work. The only things that are working are the oil pressure and temp. gauges (surprisingly, they are controlled by their own inputs independent of the cluster).

My speedo doesn't work (I assume it is the cable, so I'm not really concerned with that at this time).

The gas gauge is stuck on 3 o'clock, past full. Turn signal indicators and dash lights don't work. I grounded the gas gauge terminal on the fuse panel per Vettevet's instructions, and it went to empty, so the gauge should be fine.

I have run a jumper wire from the neg battery terminal to the dash light with the black wire clip coming off of the back, and to a couple of the mounting hex screws on the back of the cluster, but still no luck.

I have heard of grounding the gas gauge terminal, but don't know which one and don't want to take the chance of smoking something just for the sake of trying anything.

Any suggestions would be greatly appreciated.

Thanks

First thing to do is check the cluster fuse and the panel lights fuse in the fuse panel.
There are several power supplies to the dash cluster besides the cluster feed, that really only feeds the fuel gauge and the temp gauge.


Each turn signal light and the bright/dim light have their own feed, and the dash lights are fed by the gray wire from the fuse panel at the panel lights fuse, so unless the dash plug is not seated, then in order for these things to not work the problem has to be grounding issues.

It's possible that all these lights are burned out or that there are breaks in the copper circuit board wires that make all the connections but not likely.

I would try putting 12 volts on the gray wire that lights the heater light and see if the dash lights come on. It is connected directly to the dash lights wire at the dash plug at terminal 8.

If you end up pulling the cluster then you can check all the lights by grounding the cluster and putting power on the plug connectors using the diagram below. The pins are numbered 1-2-3-4-5-6 bottom to top on the left side and 7-8-9-10-11-12 top to bottom on the right.



The one below is a diagram of the connections to the lights and gauges on the back of the cluster. The gray wire is the feed wire for the dash lights and the orange wire is the ground. The purple wire feeds the fuel gauge and the temp gauge . The wire that you grounded on the fuse panel that goes to the fuel gauge is the dark green wire on terminal four. It is tan or light brown in the harness.

[dmack91]

Wow, that is as detailed as I could have hoped for.

I checked all fuse holder slots with a test light with the key on, which showed power going through each fuse.

I will try the grey wire power suggestion tomorrow.

Thanks for the help

[dmack91]

OK,

So I checked the main gauge plug and it is seated. I have power to #12 all the time, and #8 (grey) has power when the light switch is turned on, but still no dash lights.

The turn signal indicators do work (not sure if I just missed them before), but no gauge lights or fuel gauge (still at 3 o'clock).

I do notice that when the key is off, the temp gauge reads about 1/3 hot, but goes to cold as soon as I turn the key on. As soon as I turn it off, it goes back to rest on about 1/3. I put a new sending unit in and it was reading fine when the engine was running.

Getting frustrated as the only things holding me up from going mobile is this issue and trying to figure out how to bleed the front brakes since they seemed to mount the bleeder screw where you could put a wrench on it but not turn it (bought a couple of cheap 5/16" wrenches to see if I can bend one to fit).

Thanks again.

[dmack91]

Update #93

Just went back out and pulled the dash bulb holder near the gas gauge and noticed that part of the copper circuit for the bulb holder contact was loose (about a 1/2" tail - thinking it may have been grounding when the bulb holder was screwed in). I moved it around a bit and tried the lights. That dash light now works.

It looked like it was at the end of the circuit, so the other bulbs should work if they aren't burned out. I pulled one of the others and it looked dark. I will buy some new bulbs later today and see if that fixes it (hoping).

Also noticed that the inst. light fuse was a 10a, and I believe it calls for a 3a.

Now if I can only get the gas gauge to work, but I will be happy with one victory at a time.

thanks

[VetteVet]

Good morning
When you grounded the terminal that the tan wire connects to at the fuse panel it confirmed that the gauge was ok. The gauge goes to zero which means that the wire to the sender is open, the sender is not grounded to the tank or the tank is not grounded to the frame.

The sending unit could also be open but that is not very common. usually they either stick or stay at the bottom because the float has a hole in it.

Make sure the tan wire is plugged into the fuse panel and then take the wire off the tank sending unit and ground it to the body of the truck or any known good ground. If the fuel gauge goes to empty then the tan wire is ok. If nothing happens then the tan wire has a break in it at some point.

next check the sending unit to the tank mount with an ohmmeter if you have one and you should get somewhere between 0 and 90 ohms. Then check the tank itself and see if it's grounded to the cab. Be sure that you do not put any positive voltage to the tank sender since it is on the negative side of the circuit and the resistor filament will become hot in the tank and could ignite gas fumes in the tank.

[dmack91]

Thanks to VetteVet for all the help.

New bulbs (all) and fixing the short in the wire overlay fixed the dash lights.
New speedo cable fixed the speedometer.

Went through VetteVet's troubleshooting of my sending unit. I have 147 ohms from the sending unit stud to ground, so I guess my sender is shot.

Trying to decide if I want to get a new one, or visit the U-Pull-it and try to find a tank I can mount under the frame (would be nice to have at least a bit of storage in the cab).

Thanks again for the help.

[godie]

I have a similar problem but on a 78. I put in a RediRad and now my fuel gauge is out of whack. HELP!

[VetteVet]

Originally Posted by godie

I have a similar problem but on a 78. I put in a RediRad and now my fuel gauge is out of whack. HELP!

I would suggest starting a new thread about your problem because this one is several posts long and not many people are going to see your problem. It might take several replies to figure out how your radio adapter messed up your fuel gauge. Also it really should be posted in the electrical forum.

[DavTay]

Originally Posted by dmack91

New speedo cable fixed the speedometer.

Where did you get your speedometer cable?