Gauge lights

I have a 96 riv and the gauge lights work slightly but go out completly when i turn the headlights on. Anyone deal with this i'd realy like to know what my speed is at night.

Dello wrote:

I have a 96 riv and the gauge lights work slightly but go out completly when i turn the headlights on. Anyone deal with this i'd realy like to know what my speed is at night.

Simple stuff first:

I assume you tried adjusting the dimmer? If not, then next time it's dark try. Just turn the headlight knob left and right (it moves pretty easily) to the brightness you want. They should be brightest just before the detent that turns on the interior courtesy lights. The slider on the headlight control adjusts exterior headlamp delay not interior panel brightness. Now, if this works then I need to point out to you that if you do not have an owner's manual I think if you use Google or other search tool you will find a .pdf of one on line. The Buick web site used to have them as well but I don't know anymore. They are still available new, also.

Next thing to try would be to replace the lighting module I suppose, after checking the wiring.

The way it is supposed to work is...

- there's a 10A fuse INT LPS. It should be good or else you'd have no lights at all, you might want to check it though.You can check by swapping it with another known good 10A fuse. Usually you can tell just by looking but once in a while these things will blow and not look it.
- the headlamp switch has a 150 ohm variable resistor connected to a dimmer module. Current from the resistor biases a transitor to do the actual dimming. I suspect that if that transistor has gone bad or if there is a problem in the headlamp switch your instrument lights won't work right.
- trace the gray wire back through the splices and see that you're getting power
- finally, *check the ground* the light control should be grounded at the left front of the passenger compartment under the kick panel trim plate (it is on my 98)

hope this helps

Ya Thanks ill try those things. I picked up a new switch from a junk yard ill throw that in and check the grounds.

Dello wrote:

Ya Thanks ill try those things. I picked up a new switch from a junk yard ill throw that in and check the grounds.

Actually, it's probably the lighting contorl module or the dimmer module - the switch basically sends a variable voltage signal to the dimmer module, it does not really modulate the lights. I hope your headlight switch swap works but I doubt it will. Do you think you would know for sure if you did the circuit testing and not just replace parts? I think so.

We will see what you find. Good luck.

So what was the final result... I'm having the same issue...

Damn!
I realize the digital displays might need something more than a plain rheostat, but why the hell do they have to add "modules" to something as simple as the gauge lights?
Another great idea from the people that brought you the intake manifold gaskets, door sills and fuel-module lock rings...

Eldo wrote:

Damn!
I realize the digital displays might need something more than a plain rheostat, but why the hell do they have to add "modules" to something as simple as the gauge lights?
Another great idea from the people that brought you the intake manifold gaskets, door sills and fuel-module lock rings...

The module lets the BCM control the dash lights so that for instance if you turn them on during the day they *don't* dim the radio display. You can use the same signal, effectively, to modulate the brightness of the incandescent (dash gauges) and vac fluorescent (shift indicator, odometer, radio, hvac head) displays.

That said they could have simply controlled the incandescents directly and read the voltage somewhere (Stick a relatively high resistor in parallel with the bulbs and read voltage there) and used that voltage signal to modulate the brightness of the fluorescents. The solution they used was probably fewer parts/fewer failure points, if not cheaper in $$.

Eldo wrote:

Damn!
I realize the digital displays might need something more than a plain rheostat, but why the hell do they have to add "modules" to something as simple as the gauge lights?
Another great idea from the people that brought you the intake manifold gaskets, door sills and fuel-module lock rings...

I never got the point of a manifold gasket if it's an upper intake manifold. It's just air, so why would you need a $50 piece of plastic with a plenum shaped o ring on it to change a manifold? Couldn't they have just made santoprene linings on manifolds with a better flow design like the Holden intake runners? I want a Holden intake :c

Anyway is that fuse next to the door or under the seat?

albertj wrote:

Eldo wrote:

Damn!  
I realize the digital displays might need something more than a plain rheostat, but why the hell do they have to add "modules" to something as simple as the gauge lights?  
Another great idea from the people that brought you the intake manifold gaskets, door sills and fuel-module lock rings...

The module lets the BCM control the dash lights so that, for instance, if you turn them on during the day they *don't* dim the radio display.  You can use the same signal, effectively, to modulate the brightness of the incandescent (dash gauges) and vac fluorescent (shift indicator, odometer, radio, hvac head) displays.

That said they could have simply controlled the incandescents directly and read the voltage somewhere (Stick a relatively high resistor in parallel with the bulbs and read voltage there) and used that voltage signal to modulate the brightness of the fluorescents. The solution they used was probably fewer parts/fewer failure points, if not cheaper in $$.  

Hi Albert,
I do feel tacky bringing this up after 5 years of near-silence moving around Oregon since I left Marin, but I now have a problem myself with these damn lights and I haven't found any good news in the manuals or online...  I'm hoping I can find some new ideas about this system because I just can't reach up to where this stupid module is supposed to be - and searching HERE it seems that the 'dead-dash-syndrome' is extremely rare.  ;0)

ANYhow...  I did virtually all my mods back in San Rafael - including adding ONE little 194 bulb to the console compartment, off the PRNDL light & therefore the dimmed circuit.  Since I've been in Salem, I've had the 10A interior-lite fuse by the door blow twice.  Now, however, every fuse I can deduce from the manual is fine, but all bulbs/VFDs (vacuum-fluorescent-displays) are dead/dim.  

Having looked at a dozen schematics in the manual, I can tell you that your idea above about "parade mode" is sound, but that it is controlled by the LCM and then the "dim-ENABLE" terminals on the VFDs and not the variable-input "dim-input" terminals...  Basically, 1 tells the digital displays to come off of full-power, and the other tells them how dim to be.  This stupid module has only 12V from the parking lights, variable V from the dimmer knob, and output to the bulbs/VFDs.  THEY ARE LITERALLY RUNNING A DIMMER OFF OF A DIMMER, DAMMIT!!!    

What I'm wondering is:
- Is there a fuse in the Metri-pak?  The manual makes a vague mention of "fused-output" which makes no sense if it's in the module - who cares if you blow the transistor or the fuse if neither is replaceable?
- Just why CAN'T we run the bulbs/VFD-inputs straight off the bullet-proof dimmer potentiometer?  According to the test-sequence, both outputs are "yes" if 10-15 volts...
- The well-honored & traditional: what else am I missing?  

Thanks to any/everyone, and hope you are all well,
Mark

Hi Mark, I have to give this some thought.

Albertj

My instrument lighting fuse has *never* bown. I suspect you have a wiring fault somewhere. Might take a while to find. I would check that console light mod (probably fine) and look at instrument lighting wiring (including under the dash, pull the drivers side kickpanel from under the dash) and check for pinched/chafed wires. Finally check the grounds. Bad grounds do weird stuff.

WOW, I didn't expect a reply that fast - Thanks!
While 'everything' was fine for several years, I think you're right about opening up the console to check the light-mod... Even though no fuses are blown this time, it's a helluva lot easier than up-in-the-dash, and maaaaaaybe that explains the previous blow(s) and also damage to the module tranistor.
M

Eldo wrote:

WOW, I didn't expect a reply that fast - Thanks!
While 'everything' was fine for several years, I think you're right about opening up the console to check the light-mod...  Even though no fuses are blown this time, it's a helluva lot easier than up-in-the-dash, and maaaaaaybe that explains the previous blow(s) and also damage to the module tranistor.
M

If the fuse is not blown maybe the module transistor was damaged such that it won't work right anymore.

This reminds me of something: I have an issue I need to fix at some point. Under my passenger seat the insulation on the wiring to the seat position switch cluster is chafed. Once in a while (every so many years) they short onto the seat rails (a passenger puts something under the seat... I just don't do that...). The thermal breaker blows (you can smell it if you know what to smell for, it's a really faint ozone-y non-odor, though). I reach under the seat, then, and pull the wires toward center of the foot well and after a few minutes the breaker resets and the seat works again. I really should pull that effing seat and fix the insulation on the wires. Some self-fusing silicone tape ought to do it and would let me set the wires so they don't pinch again (more body than vinyl tape and no adhesive to get warm and melt around). Car is down for some other work, I think I will go ahead and fix those wires while I am at it.

How this affects you: your issue may be you're looking for a stupid intermittent short. I don't envy you. I imagine it would not hurt to check the glove-box light and switch and ashtray light wiring while you are at it. But I would start with wiring on the INT lighting circuit that you did mod and then just follow the wires.

By the way I checked real quick - the instrument panel dimmer modules (that transistor-looking gadget) are available from rockauto.com for less than $39 and if you check by clicking that part number you will see they were used on about every mid 90s GM BOP and Chevy. I bet you can have 1-2 of them from a pick-n-pull on a gimmee. IIWY I'd consider printing that list then making a Saturday morning run to a picknpull and get 1-2 of them, then find the wiring glitch.

All good ideas, Albert, and the console/glove box/ashtray wires have been disturbed this last year cuz of a dying blend-air-door motor on the passenger side... plus they're much easier areas to check than behind the instrument cluster.  (Forgot to mention that besides my traditional spine & size problems getting to the steering column brace, I just had rotator cuff & biceps tendon repairs 2 months ago.)  And thanks for the RockAuto tip, I would've probably just assumed these were dealer unobtanium.

Also my brother, the mechanic until around 2010, claims he never had to replace one of these modules but did replace more than a few headlight switches for dead dash lights.  So that's another thing I can do from up top, pull the switch & jumper the dimmer output on the connector.

Thanks again, and I'll let you know what the final result turns out to be - whenever that happens.

Mark, not relevant, but my 2-year-old daughter spotted your avatar while I was reading. She said, "Race car. I want to watch." So we pulled up some highlights from the Daytona 500. I think she thinks your Riviera finished at Daytona!

AA wrote:

Mark, not relevant, but my 2-year-old daughter spotted your avatar while I was reading. She said, "Race car. I want to watch." So we pulled up some highlights from the Daytona 500. I think she thinks your Riviera finished at Daytona!

OMG, that is sooooo cute, Aaron!
Hahahahaha!!  

Some time in the future you can show her San Francisco's Golden Gate from the Marin Headlands from the old calendar cover....

(BTW, I disassembled the console and part of the dash today, and then the ignominious Northwest rain came down in torrents... Sighhhhh)

Eldo wrote:

All good ideas, Albert, and the console/glove box/ashtray wires have been disturbed this last year cuz of a dying blend-air-door motor on the passenger side... plus they're much easier areas to check than behind the instrument cluster.  (Forgot to mention that besides my traditional spine & size problems getting to the steering column brace, I just had rotator cuff & biceps tendon repairs 2 months ago.)  And thanks for the RockAuto tip, I would've probably just assumed these were dealer unobtanium.

Also my brother, the mechanic until around 2010, claims he never had to replace one of these modules but did replace more than a few headlight switches for dead dash lights.  So that's another thing I can do from up top, pull the switch & jumper the dimmer output on the connector.

Thanks again, and I'll let you know what the final result turns out to be - whenever that happens.

your brother is probably right & it is easy to test... and the HL switches are still available IIRC, check rockauto

Well, I was HOPING he was right... I have an extra headlight switch.

But, NOOOO.  I pulled the left trim panel around the fuse box & unscrewed the headlight switch. What I eventually found out to be the under-rated dimmer rheostat compared to the traditional, wire-wound & ceramic dimmers - and thus the reason for the NEED for the transistor's current amplification - works perfectly.

It adjusts from 5.5V output to 11.5V (engine off.)  I also tried bypassing the output to the dimmer module & nothing happened.  So unless I (i.e. when my skinny, flexible buddy can get under there) find a wire problem down there, somehow I've cooked the dimmer module.  But that still leaves the reason, doesn't it?    

Check the resistance as you sweep the knob against that of the replacement switch, to be sure.  

Check the wiring with the switch out of circuit - hook up a meter then wiggle the harness to see if anything changes.  You just might find a/the problem.

FOUND IT, BOYS!

I was a moron for not digging deeper into the schematics when that fuse blew out last time...  

If I had done that before this failure, I would have found out THEN that the mini door-lights, passenger climate control and the console PRNDL lights were on the dimmer circuit!  When I adjust the dimmer, I always look at the gauges and never imagined those other things were not on straight parking-light power...

Without that information, and considering how long & intermittent the problem was, I never made the right connection (pardon the pun.)  Whether it was original, or because of the Scotch-Loks to the console-compartment light I added, the factory positive (naturally) wire to the shift-quadrant lights was being rubbed by the base of the shift lever.  I can't BELIEVE how intermittent it was.  

I can't complain about the mexican-made Motorola transistor - it gave me two chances to figure it out and fix it with just 4 screws, some clips and 2 inches of electrical tape.  What's interesting is that both old & new modules are stamped with the old Mallory logo, and I don't think they exist anymore.  At least, not looking at current logos for ignition systems or looking at my DuraCell batteries...

Anyhow, by lifting the dashpad, removing the dash panel, removing the knee bolster, and pulling the lamp control module and turn-flasher & bracket I was able to get my big ol' hands in from the front and replace the module on the left/rear of the steering column bracket - with only 5 cuts to my left hand.  

I can't get a decent photo under the dash, but here's what the dimmer module looks like:




As always, thanks for your input,
Mark

Thanks for the update,and glad you found the gremlin.

Hey Albert, I forgot to ask something....

Anybody know what the hell that "double-reversed-fuse-holders" are, that are taped together near the white bracket where the enable-relay/LCM/BCM are?  I couldn't find it in my eSI-electronic manual...

Eldo wrote:

Hey Albert, I forgot to ask something....

Anybody know what the hell that "double-reversed-fuse-holders" are, that are taped together near the white bracket where the enable-relay/LCM/BCM are?  I couldn't find it in my eSI-electronic manual...

...can you email or post a pic? so I can compare to my Riv. I don't want to say until I confirm what I am supposedly looking at.

That's OK, it's not a big deal - and unfortunately, I've finally buttoned everything back up...
On the bright side, since I had the whole damned dash apart, I fixed my cassette player.  

It's not actually attached to that white plastic bracket that holds the lamp & body control modules, it's just hanging there - two individual 'regular-size' autofuse holders taped back to back with white paper tape that only has the amperage printed on it, with no indication what the hell they're for...