gauge lights suddenly stopped working

[rpm148]

just had a little work done on my 85 fj60. got an h55f, new clutch, master/slave cylinder, t-case rebuilt, and while it was there, found that the fusible link was blown, so that was replaced.

I'd like to preface this by saying that I have a very limited technical knowledge, but am very curious and a quick learner.

while driving it home, I noticed all of a sudden that the lights on the gauges, behind the heater/ac controls just suddenly stopped working. The gauges themselves work. the AC light comes on when I press that button. The ac/heater still work. the light for "brake" "high beams" and "4wd" still come on. dimmer switch doesn't do anything. dome light still turns off/on. checked the fuse for gauges (7.5 amp) and that looks fine. any suggestions on where to start trouble shooting, or if a newbie like me should even attempt this or just take it to a shop?

thanks in advance for your input,

RPM

PS if anyone in western washington wants to help me out and teach me some stuff, I live in Kitsap County WA, across the water from Seattle, and will be available next week!

 

[3_puppies]

don't suppose that someone turned the dimmer down?

 

[CMoss]

Hello.

Did you ever get any answers to your instrument guage light problem? I have the exact same problem with my 88 FJ62.


I just re-carpeted and re-upholstered my 1988 FJ62 this weekend and, once clomplete, all of the background lights that illuminate the three guages ( tach, speedometer, fuel) as well as the light that illuminates the heat / AC temperature control quit working at the same time. None of them work.


However, all of the following lights still work....brake warning, high beam, battery warning light, blue AC button light, defrost light, digital clock, ATP oil temp light on AT shift station, fasten seat belt warning light, stereo light. These light all still work.


Only the actual lights that illuminate the three separate gauges and ac/heat temp contol are not working.


Any suggestions?

 

[mobydick]

Check the dimmer switch and wiring first. It's easiest. I have often bumped that dang gnob and put my own lights out.

 

[CMoss]

Thanks for the reply. Just bought a replacement dimmer switch. That didn't work. Now I have an extra dimmer switch. This is frustrating.

 

[Godwin]

Are the running lights still working? Once had an issue with loss of gauge lights and running lights because the fuse kept blowing. Problem was an uninsulated live wire associated with an aftermarket stereo install that was grounding out.

 

[CMoss]

Thanks for hanging in there with me on this one. Yes, the running lights are still working. There is an aftermarket stereo in the vehicle but it has never caused a problem. My son loves driving my 62 because we have both fixed it up together and he's finally at the age where he realizes how cool it really is, but I cannot let him drive it at night until I get these guage lights fixed. I used a heat gun to put down sound deadening material before new carpet but have checked and rechecked to make sure that I did not burn any wires in the process. I'm missing something. Like a needle in a haystack.

 

[Godwin]

Thanks for the reply. Just bought a replacement dimmer switch. That didn't work. Now I have an extra dimmer switch. This is frustrating.

Have you tried bypassing the rheostat? Pull it out and jump the appropriate wires. If you gauges work then the problem lies with the dimmer switch, if not you've at least ruled that out.

 

[CMoss]

Great idea. I did have my local mechanic do that and he said it blew the fuse everytime he tried bypassing the dimmer so he said I needed a new rheostat. Ordered a used one from Cruiser Parts and plugged it in but that didn't solve the problem. I guess there's a chance that the replacement rheostat was bad too but I doubt it. Cruiser parts said they tested before shipping to me and that it worked.
Rheostat/light dimmer 81-90
Complete assembly, works fine. Controls instrument light brightness.

$35

 

[Godwin]

Pull the rheostat, check the fuse, connect the wires and see what happens. If the fuse blows you have a short somewhere.

 

[Bear Lake Cruiser]

I believe the dimmer switch works by controlling the ground and comes after all the lights in the circuit.

 

[CMoss]

Ok. Will do. I imagine the fuse will blow as that is exactly what my local mechanic did.
I saw the comment that The dimmer switch works by controlling the ground and comes after all the lights in the circuit.What does that mean to a dummy like me? Should that give me a clue regarding where should I even begin looking for a short that will cause only the tach guage, speedo guage and fuel gauge and the air temp panel to not work.
I am not positive, but I think this short also affected the auto transmission shift column as well.....although the ATP light does still work but the park, neutral, reverse, drive etc lights do not work. Thanks.

 

[Bear Lake Cruiser]

Do you have a wiring diagram from the factory service manual for chassis? If not do a search on this forum for a free download the diagrams are fairly straightforward and can offer clues where to test voltages grounds continuity etc

 

[slcfj62]

Let me see if I can help a little. Yes, the rheostat is on the ground side of the circuit. What this means is that all the dash lights are connected to the fuse on the positive side of the bulb (solid green wire) and to the rheostat on the negative side (white/green wire). The other side of the rheostat connects to ground. If your mechanic blew the fuse when he jumpered the rheostat, then he picked the wrong wire. The rheostat has three wires connected to it. The white/black wire goes to ground, the white/green wire goes to the dash lights, and the solid green wire goes to the fuse. Your mechanic probably connected the solid green wire to the white/black wire which would blow the fuse. If you jumper the rheostat via the white/green and white/black wire, it probably won't do that.

All of the dash lights as well as all the running lights and tail lights all come from the same fuse, the 15 A TAIL fuse. So, if your running lights work, the fuse is good and 12 volts is being supplied to all the dash lights. These are the green wires to every dash light. So, find a dash light and see if the green wire has 12 volts when you turn on the parking lights. If so, then your problem is on the ground side of the circuits--enter the rheostat which stands between your dash lights and ground. Jumpering the rheostat via the white/green and the white/black wires should help you determine whether the rheostat is at fault, or if you have a broken ground wire between the rheostat and ground, which is the white/black wire.

So, go out and do a little sleuthing and report back.

By the way, the rheostat is not just a potentiometer, it has some circuitry in it and I believe it regulates current rather than voltage to dim the lights. And since the rheostat is on the ground side of the dash lights, this is the reason you can't get your aftermarket stereo lights to dim with the dash lights no matter where you connect the wire. Nearly every vehicle on the road has the dash light dimmer on the 12 volt side of the light bulbs. Toyota chose a different path.

 

[gregnash]

Check your fusible link wires.... I had the same issue not to long ago (except my stereo died as well) and found out that it was one of the fusible link wires that was broken. Once it broke it would make random connection and everything would work for a short time but ended up frying the receptacle for the fusible link on the positive battery cable as well as the fusible link side.

 

[CMoss]

Good stuff. Thanks for all f the details. Will try tomorrow and report back.

 

[cruiserpilot]

CMoss - good luck. I have the exact same problem, just have worked it when the time permits. Its been driving me crazy for 4 yrs. I really hope you figure it out and report back. slcfj62, thanks for the info.

 

[CMoss]

Well mystery solved. After spending two days virtually dismantling the entire vehicle and throwing a few tools, I found the problem with the help of a friend with a lot more common sense than me. When I reinstalled the front drivers seat after reupholstering it, the seat bracket pinched the pigtail connector from the shifter assembly that is located very near the front right seat bracket. See attached photo. Unbelievable. Thanks to everyone for their input and advice. Two photos attached.

 

[slcfj62]

Yay! One thing to always remember when troubleshooting is to revisit anything you or someone else did right before you noticed the problem. Sometimes coincidences shouldn't be ignored.

Good job.

 

[ReelBigFisch]

Let me see if I can help a little. Yes, the rheostat is on the ground side of the circuit. What this means is that all the dash lights are connected to the fuse on the positive side of the bulb (solid green wire) and to the rheostat on the negative side (white/green wire). The other side of the rheostat connects to ground. If your mechanic blew the fuse when he jumpered the rheostat, then he picked the wrong wire. The rheostat has three wires connected to it. The white/black wire goes to ground, the white/green wire goes to the dash lights, and the solid green wire goes to the fuse. Your mechanic probably connected the solid green wire to the white/black wire which would blow the fuse. If you jumper the rheostat via the white/green and white/black wire, it probably won't do that.

All of the dash lights as well as all the running lights and tail lights all come from the same fuse, the 15 A TAIL fuse. So, if your running lights work, the fuse is good and 12 volts is being supplied to all the dash lights. These are the green wires to every dash light. So, find a dash light and see if the green wire has 12 volts when you turn on the parking lights. If so, then your problem is on the ground side of the circuits--enter the rheostat which stands between your dash lights and ground. Jumpering the rheostat via the white/green and the white/black wires should help you determine whether the rheostat is at fault, or if you have a broken ground wire between the rheostat and ground, which is the white/black wire.

So, go out and do a little sleuthing and report back.

By the way, the rheostat is not just a potentiometer, it has some circuitry in it and I believe it regulates current rather than voltage to dim the lights. And since the rheostat is on the ground side of the dash lights, this is the reason you can't get your aftermarket stereo lights to dim with the dash lights no matter where you connect the wire. Nearly every vehicle on the road has the dash light dimmer on the 12 volt side of the light bulbs. Toyota chose a different path.

@slcfj62 - Thank you for your explanation.

I've been searching the forums for help troubleshooting my inop dash lights. Upon disconnecting the circuit board/gauge cluster connections, I was getting a 160 ohm resistance reading to ground on what I was pretty sure was the ground portion of the circuit (runs to the rheostat).

Following your tip, I tried the jump and it worked...Dash lights working but dimmer out of commision..