briefcase

Hey there, I've got a 91 pickup and I'm trying to diagnose why my dash lights won't work. They stopped working last fall, and while I tried to figure out what happened to them back then, we got gifted a much more fuel efficient car to use over the winter so it fell by the way side.
Oddly enough, the dash lights slowly started not working, sometimes not turning on when the light control switch was turned on, and other times working properly. They slowly got worse and worse, with the frequency that they would work properly diminishing over probably a couple of weeks or so.

So far I've done the following to try to diagnose the issue:

1. Checked all fuses, with all registering continuity.
2. Disconnected the dimmer switch, testing for continuity, and then bypassing it just in case. Dimmer switch does have proper continuity, but I've left it bypassed for now.
3. Tested continuity of light control switch as per page BE-19 of the lighting system manual. http://www.gvrdeu.org/Toyota%20Manua.../4lighting.pdf
Proper continuity was found for all tests.
4. Took apart the dash, and tested continuity of the bulbs in the cluster, all bulbs tested had continuity, so I'd guess that means they haven't burnt out? Please let me know if it's possible for a #194 bulb to have continuity but also be burnt out.
5. Tested for continuity from the cluster to the wire going to the dimmer switch, then from the dimmer switch wire to the plug that goes into the cluster gauge. Each respective test came back with a positive continuity.
6. Tested continuity on the back of the cluster gauge for the "wires" that go from the plugs to the bulbs themselves. Positive continuity across all the "wires"

So I'm left scratching my head. As far as I can tell, the light control switch is properly telling the wires that go to the dimmer switch to receive power or not.
The dimmer switch wire then makes its way to the cluster gauge where as far as I can tell all the continuity lines up (I haven't taken a direct multimeter measurement to see if voltage is actually getting there, just using continuity tests).
And the bulbs don't appear to be burnt out, and still have continuity between contacts.

I know that the dash lights are associated with the tail lights as well, but my tail lights are working properly.

The only lights on the entire truck that aren't working are the illumination lights in the gauge cluster, as well as the illumination lights for the temperature control.

Maybe a ground has gotten loose? or there's a short somewhere? Wouldn't a short blow the fuses? I'm just left scratching my head trying to figure it out.

scope103

Hey! This giving advice on YotaTech is easier than I thought!

Yeah, you know what I'm going to say. Remember that the dimmer switch is on the GROUND side of the combination meter lamps. I assume you have no tach, so your dimmer is a two terminal device. With the lights on, the lamps side (WG) should have battery voltage to ground (with the dimmer disconnected, so there is no current through the lamps), and the other side (WB) should be at ground. Grounding the WG side should turn on the lights on the combination meter.

Does your glove box light work? That's not on the dimmer, so when that switch closes (when you open the door) the lamp should light, as long as the taillight relay is closed.

briefcase

I do have an aftermarket tach but it's connected to a running light exclusively in the cluster and shouldn't affect the dash lights.

I don't believe my 91 has a glove box light unfortunately, i just went out there to check and couldn't find anything.

I've grounded both wires that would normally go to the dimmer to no avail.

What do you mean by WG? White/green wire perhaps? The two wires that I have going to the dimmer are Red with a black stripe, and White with a black stripe respectively.

scope103

The colors I provided come from a 1993 EWD. They usually don't change much, but yours must be different. In the '93, RB is from the the taillight relay to the light control switch, which grounds it to close the relay.

Grounding wires is sometimes useful (until you blow a fuse), but the reason you have a multimeter is so that you can check for voltage. GIven that your taillights are working, it seems clear that your problem is on one side or the other of the combination meter. My EWD shows the power to combination meter is a G wire on pin 2 of connector C8 to the combination meter. If you don't have battery voltage there (with lights on), work back towards the integration relay.

(The dimmer is a 3-terminal device with a factory tach; 2 terminal otherwise. This has nothing to do with after-market additions.)

briefcase

I'll try to figure out if I have voltage at the the pin I can trace to the lights, and work my way around that. I guess it will be pretty clear if I have voltage all the way to the lights but they don't light that they'll need to be replaced.

I'll report back when I've tried some more things. Thanks for the help.

scope103

It strikes me as very unlikely you took out a half-dozen bulbs at once. It strikes me as likely that you have a single connection dislodged somewhere. You could have battery voltage right up to the combination meter connector, but right on the other side you could have a crack in a pc trace. Or if you have an open on the ground side of your combination meter, you'll have battery voltage all the way to the combination meter and up to the bulbs. Use your multimeter to find where you have voltage. If you have battery voltage on one side of a bulb, and ground on the other, then I would agree the bulb probably needs to be replaced.

Dom91

I'm having exact same issue

briefcase

So, I was able to trace voltage all the way back to the daytime running light relay, which is only is Canadian cars I think (I'm Canadian). One of the pins was only receiving intermittent voltage, why, I don't know.

While I wasn't able to fully diagnose exactly what was going wrong with the relay, whether it was a bad input that resulted in the bad output I was getting, I was able to overall solve my problem.

There's an additional pin on the relay (right next to it) that functions exactly how the faulty pin does, only sending voltage when the light control switch is turned on. So I just spliced the wire into that pin and voila. It's not a great fix, and it doesn't get to the real root of the problem but it's doing the job just fine now.

I probably just need to get a new running lights relay, but in the mean time, and until I find one, this'll have to do.