When the SU wire is disconnected from the connection, the gauge bottoms out UNLESS the wire is grounded to something (ie :frame,body)

 

well i went the junk yard today and i got some other guages out of a bronco that also had the factory tach set up in it so i got all the stuff i needed off that cluster to run the tach in my truck it worked for a bit then quit i mesed with it had it working then shut off the truck went to start it back up a few hours later and itt did come on again i tryed messing with it some more but nothing so i just took it out and put my old stuff back in there except the other guages i got also got a hand ful of the cluster voltage regulators off ford vans broncos and trucks and the one i bought from napa must have been juunk so that was 29 wasited on that when i got a had full of those for 2 dollars but at i know what my truck tachs at at 65 its at 3000 RPMS at 60 its a tad up at 55 its 2500RPMS it looks cool i liked how it looked and the tach worked with the the cluster instruments but i guess it wasnt maent to happen if i stumble across another set up out of soemthing else i will definaltey grab it cause there cheap and see if it will go back if not oh well at least my guages are working good oil presure is reading what i thought a new engine should and the temp is reading good i guess it must have a cold thermostate in it cause hell i can take off the cap after runig it up the road and back and dip my figure int eh coolant and hold it in there forever its just warm tot he touch trucks from arizona so im sure it dose have that or none at all either way thanks for your help ill keep everyone posted

 

I'm having a simular problem with my 79 F100 302... The guages worked fine till I took it to the transmission guy and when I got it back they were all running too high but it wasn't a constant thing. They were moody, sometimes running too high and sometimes running normal. Replaced the instrument panel voltage regulator and now they ALL run too low. The gas read 3/4 when it's full etc. Did't realize the tranny guy had left a ground undone and redid it just the other day. Now they're back to their old moody behavior but instead of running too high, they're running even lower i.e. gas guage reading 1/2 when it's full. So what are your thoughts on this.

 

Bang on the dash with your fist and see if they change.

 

been there....

done that ...

fixed the blinker light that way ....

but not the guages....

 

Are you sure they ALL read low or high? When they are "moody" they all move in concert with one another? If so, you still have a grounding or voltage supply problem to the guages. If the fuel guage seems to be the worst one of the bunch, you may have grounding problems at the fuel tank, or a bad sending unit.

 

Yes, they all move together when they do this. I used the gas guage as an example becuz it's easier to see and to explain. I know it's the guages or something electrical becuz I have a mechanical temp guage connected also and it doesn't get moody. You said voltage supply problem to the guages. Meaning either one of the two voltage regulators??? I've replaced the instrument panel voltage regulator but I haven't replaced the other one on the fender well. Could that be causing the problem???

 

p.s. I just went outside with my dad (who is pretty clueless about this as well) and we did some voltage tests... I pulled the instrument cluster far enough out to get to the regulator. We tested it across the two connections and it was FLUCTUATING from 5 to 10 but we weren't able to get a good connection. We disconnected both connections and the power to the regulator was reading steady 14/14.5. We connected that one connector only, and coming out of the regulator it was PULSING from 0 to about 5. Is that normal? It tested good at the voltage regulator under the hood and every where else.

 

The ICVR only runs on 5 Volt pulses.

The gauge & idiot light systems actually works on the premise of the *Grounding out* of the sending unit.

 

so I need to check that each of them is very well grounded??? They screw directly into the block or intake and it's grounded.... I haven't looked at the gas guage sensor thing to see how well it's grounded but the other two should be grounded to the block ... so what else could it be?

 

Because they work on a gradual amount scale and not quickly,the problem with yours maybe you don't have that ground strap from the back of the engine to the cab.
I can't remember iif we talked about this with you before Connie.

Also, I'm sure you knew there are different S/U's for gauge vs Idiot light.

I'm sure though, about the problem with the Fuel S/U that it is grounding problem inside the tank to the tank.

Rust can penetrate the joint between the two nd cause problems.

 

So, even though it happened all at the same time, and all three of the guages are being stupid together, it could be solely the ground on the gas guage? I put the block to body ground back on just a few days ago and it was immediately after I connected that ground, that it started it's moody behavior again only now that it is connected, all three of the guages are reading lower than they were before and they were reading too low before constantly.

I am an electrical ignoramus. I understand the very very very basic basics. That's just about all. I'm talking, connect the battery this way, if it's dead, boost it this way, if it clicks, clean it here here here and/or here. I honestly didn't know there were different sending units for idiot lights vs guages but it does make sense that there should be when I think about it.

I have been trying to figure this problem out for a year now. It is progressing into something that has become aggravating to the point I just want to put the truck away and drive something else for a while so I don't have to look at, or think about it. Unfortunately that's not an option and I'm at the end of my rope. I think I have asked about this in the past but anything I've tried from those previous posts obviously hasn't worked and I thought after this amount of time and a little new information maybe there would be some new perspective or ideas.

I am seriously coming to the end of my rope and about ready to say that this problem has beat me becuz I can't figure it out. I don't have the knowledge yet to figure it out and everything that I have tried means absolute squat becuz I can't even figure out why it didn't work when it doesn't and usually don't understand why it might work before I try it. Thanks anyway for the suggestions. I'll check the gas tank sending unit ground and if it appears clean and good then... then I'm really lost ... g'night, Merry Christmas, and thank you.