[Unresolved] Gas and Temp Gauges not Working

[Ram50Guy01]

So, my gauges are being problematic. Spedometer works ofcourse. My gas and temperature gauge however do not. They will randomly work here and there but only for literally 2-3 seconds and tend to move back and forth in the process. I’m thinking it’s a bad ground but I don’t have any idea. I am currently at work so just wanting to see if I can get some information or tips before I get home and mess with it.

[Ram50Guy01]

So, my gauges are being problematic. Spedometer works ofcourse. My gas and temperature gauge however do not. They will randomly work here and there but only for literally 2-3 seconds and tend to move back and forth in the process. I’m thinking it’s a bad ground but I don’t have any idea. I am currently at work so just wanting to see if I can get some information or tips before I get home and mess with it.
Also, it’d be pretty nifty if I could get information or diagrams on the wiring and the actual 7v converter location and whatnot

[FMS88]

Also, it’d be pretty nifty if I could get information or diagrams on the wiring and the actual 7v converter location and whatnot

Since you didn't mention a tach, I'm assuming you have the non-tach cluster. Here's the schematic for an '88. I'd be surprised if it differs for your '89.

http://www.mightyram50.net/vbulletin/attachment.php?attachmentid=28221&stc=1http://www.mightyram50.net/vbulletin/attachment.php?attachmentid=28222&stc=1

You're right to suspect grounding issues since both gauges act similarly. The ground point for the cluster is behind it (see below). Inspect and clean the contacts of the two connectors that plug into the cluster if they're discolored or corroded. Also, clean the ground points of the negative battery cable in the engine bay. There are three or four points along the cable. Keeping those connections solid and clean can correct or prevent many electrical problems. If this doesn't do it, check fuse #7 and the connector to the ignition switch for poor contacts. If the problem still persists, get an Ohm meter and check the continuity of the relevant wire.
I don't know the location of the 7v converter. The diagram above shows a voltage limiter (*3) as part of the cluster. It's probably in the circuit board.

Here's the cluster ground location:
http://www.mightyram50.net/vbulletin/attachment.php?attachmentid=28223&stc=1

[Ram50Guy01]

I took the cluster out last night with what little time I had to mess with it. I checked continuity across the cluster which was fine. The only issue was I had no voltage coming in at the connection points for those two gauges and the 7v. I can’t really read the diagram you provided as it shows blurry on my end.

[FMS88]

In the larger connector to the cluster, check continuity and resistance of the black (ground) wire, and with the key in the ON position, verify you have 12v at the red-on-white wire at the connector. Here's a pic of the connector:

http://www.mightyram50.net/vbulletin/attachment.php?attachmentid=28226&stc=1

The wire labeled "to tach" is the power source to the gauges and lights, too. The yellow wire is from the fuel gauge. It's not energized. It's a variable resistance ground the gauge "reads" to display the tank fuel level. Similarly, the red-on-yellow wire in middle size connector is from the resistance type temp sender on the intake manifold below the thermostat.
Can you see any evidence of burned or broken tracks in the circuit board?

[Ram50Guy01]

Okay, so I’ve never really used a multimeter but from what I’m seeing every resistor connection is reading 000.0 while my ground reads 0.5-.9
I was checking continuity between stuff to try and identify where the connections were going and I was getting a very weak beep from these two green wires on this severed connection while having the neg end of my multimeter jammed against the yellow wire in the center connection. https://ibb.co/Z1fFZr8http://www.mightyram50.net/vbulletin/blob:http://www.mightyram50.net/464de2cc-7b70-4f87-9596-ca963e371868

[Ram50Guy01]

Okay, so I’ve never really used a multimeter but from what I’m seeing every resistor connection is reading 000.0 while my ground reads 0.5-.9
I was checking continuity between stuff to try and identify where the connections were going and I was getting a very weak beep from these two green wires on this severed connection while having the neg end of my multimeter jammed against the yellow wire in the center connection. https://ibb.co/Z1fFZr8http://www.mightyram50.net/vbulletin/blob:http://www.mightyram50.net/464de2cc-7b70-4f87-9596-ca963e371868http://www.mightyram50.net/vbulletin/attachment.php?attachmentid=28228&stc=1

[Ram50Guy01]

Nevermind it seems like that connection has something to do with the lights as opposed to the gauges. I’m gonna continue looking around until I get more info

[Ram50Guy01]

http://www.mightyram50.net/vbulletin/attachment.php?attachmentid=28230&stc=1

[FMS88]

http://www.mightyram50.net/vbulletin/attachment.php?attachmentid=28228&stc=1

Those two green wires go to a sensor on the brake master cylinder reservoir. The sensor lights the cluster Brake lite if the reservoir level drops too low.
I don't know about the two blue connectors. They're both unconnected on my truck. They might be connectors for A/C components which I don't have.
Also, sent you a PM - trying to get legible images of the cluster wiring to you.

[FMS88]

The voltage limiter depicted in the cluster diagram is part of the fuel gauge and the limiter drops the voltage to 7v for both gauges. I found continuity between the IGN+ and the 7v terminals of the fuel gauge and only 1-2 Ohms resistance. If no continuity or very high resistance, the limiter is probably toast. Here's the manual's tests for the two gauges:

http://www.mightyram50.net/vbulletin/attachment.php?attachmentid=28232&stc=1

[Ram50Guy01]

I got normal readings between 7v-TU and 7v-FU, However IGN+ to E was reading 1.2 Mega Ohms. What should I do from here?

[FMS88]

I got normal readings between 7v-TU and 7v-FU, However IGN+ to E was reading 1.2 Mega Ohms. What should I do from here?

That Ohm reading doesn't sound good. What do you get between IGN+ and 7v?

[Ram50Guy01]

Yeah, I tried that and got no continuity and 0L on Ohms. I also put my terminals on my capacitors while in the capacitence mode. I got a 530~ reading on the one closest to the temp. And nada on the one closest to the gas.

[FMS88]

Yeah, I tried that and got no continuity and 0L on Ohms. I also put my terminals on my capacitors while in the capacitence mode. I got a 530~ reading on the one closest to the temp. And nada on the one closest to the gas.

My electronics skills are very limited so I can't interpret results of the capacitor tests. But from the IGN+ - 7v terminal test, I think the voltage limiter in the fuel gauge has failed. As a final test the gauge can be removed fairly easily and inspected.
If you want to do so, remove the two screws and surrounding clips to release the clear front cover. Remove the two screws next to the speedo cable and the two E and EGR screws that form line between the speedo and large connector. Pull the speedo and black face out of the white housing. Remove the three hex nuts and one E screw to separate the gauge. Look for burnt or broken parts. I'll post pics of the one I have so we can compare.

Pictures: Inside looking down. The FU post and bimetal coil of the needle on the left, 7v post middle, and the IGN+ right. Voltage limiter is to the far right:

http://www.mightyram50.net/vbulletin/attachment.php?attachmentid=28233&stc=1

The limiter from the side:
http://www.mightyram50.net/vbulletin/attachment.php?attachmentid=28234&stc=1