New to the forum here, Just recently picked up a 2002 base to replace my 94 miata as a new DD. It had a few issues with it,one of which being the tachometer doesnt work, no lights or anything.

speedometer works and all the gauges in it but the backlighting doesnt appear to be functioning.

Ive ran through all the fuses and havent found any that are blown. ive also reomoved most of the interior to look for corrosion from sunroof drains, despite there being some moisture under the carper the fuse box and BCU seem to be ok. though just for precautionary measure ive removed the bcu and have had it drying for 2 days no and no difference.

any help would be appreciated.

also car passed emmisions fine and gets OBD power

 

Swapped on a different speedometer.

No difference, except now the yellow warning light is on.

Still no backlights or teach power.


In a recent speaker upgrade I got to see all the wiring behind the panels and nothing there looked bad or out of place.

 

bump

 

Your CEL is on now? Double check the fuses and definitely make sure that none are blown. I did find these threads on NAM here and here. See if they may be helpful.

 

Did you check the inside of the BCM and the connections for corrosion.

 

yes ive removed the bcu and let it dry for a few days but all the wiring and connectors looked well.


going to check the fuses again.
my scangauge keeps showing code p1692

nothing works on the tach, no backlight or warning lights

 

If you open it up and see corrosion, it might need replaced. Also check really close at the harness plug, they have been known to cause issues with minimal corrosion you can see in the plug harness pins. 61356982114

https://www.northamericanmotoring.co...le-issues.html

 

So those threads I posted said the dash lights and tach are both controlled by circuits in the speedometer. Suggested in one is that the speedometer uses F21 and others that connect are F40, F9, F5. Check those out the lines again etc. and just make sure you haven't missed anything. For P1692 I found this here. (The poster Nick works here). Here is a thread on NAM with it and someone said they were going to try out the battery. Maybe you can post in there and ask if the OP found the issue.

 

just swapped all those fuses with new ones, still no difference.

i also replaced the battery last week and have been monitoring voltage since. hasnt given me any issues, even sitting for says it will start.

also replaced all the speakers and inspected all wiring visible .

i guess next im gonna start jumping the speedo to the tach.


the bcu even had the splash shield on it. i dismantled it and inspected it.
everything else electronic seems to work.


if a reprogram wasnt necessary i would have swapped in a new bcu by now

 

Ok, just narrow it down and check everything. Most problems are the BCM getting wet and causing all kind of issues.

 

Not sure if it helps, I have a similar issue which was diagnosed as a faulty speedo.

 

tried that.
currebtlybusing a speedo i got from ebay a week ago

 

Gotcha, I was under the impression used speedos wouldn't work.

 

Even one shorted/wet plug connected to the bcm can mess everything up. Check aftermarket stereo wiring. I had moisture in my trunk under the carpet shorting out the cd changer plug , caused no dash lights to work including turn signals and high beam indicators on the tach. I hit the plug with a hair dryer after figuring it out and it went right back to normal. (I had just installed new headlights so I thought it was my headlight wiring and completely disassembled all of
My wiring and the tachometer itself before finding the simple issue. Could be any plug shorted out due to moisture, as long as it is controlled by the bcm, I'm sure it would throw off the whole computer :/

 

i did look at the plugs today.
i have oem radio without cd changer
i will inspect rhe wiring further and hitbit with a hair dryer

 

Do you mean the night illumination when you turn on the headlights? Does anything else on the dash light up (AC/heater controls, toggle panel, etc)? The night illumination is all on one circuit, driven from the speedometer. The speedometer is connected to fuses F5, F9, F21, F40. The tach is entirely controlled by the speedometer through a 6 wire harness.

 

no backlights anywhere.
only the radio screen and odometer have backlight, nothing else


if you adjust the dimmer thats all that changes

 

bump still chasing this down.
looking for a wiring diagram for the speedo
im trying to find what powers the backlighting

 

Wiring diagrams can be found in the Bentley Publishers service manual (you'll probably want to purchase this if you plan to do DIY work on the car). For wiring diagrams, better to get the BMW WDS software on DVD from eBay (search eBay for "BMW WDS").

For the speedo and tach, there isn't much to see in the diagrams because most functions are performed by black box digital electronics in the circuit boards. In other words, most things are software controlled through the CAN and K digital bus and not hardwired.

Here is the diagram for dash illumination, which is carried on wires marked GR/RT (German abbreviation for gray/red). The lighting signal comes from the speedo electronics and goes to the gauges, switches and buttons. The "Instrument cluster control module" is inside the speedo, and the "Auxiliary instrument cluster module" is the tach. The lighting is probably turned on by the Body Control Module (in the passenger footwell) sending messages to the speedo over the CAN bus.


Here is the full diagram for the speedo:


Here is the wiring between the tach and speedo (also visible in the speedo diagram above). Perhaps you could verify that the tach has power on the V_BATT wire.

 

thanks so much will start looking into it today


cleared my p1692 and is hasnt come back

 

Sorry to bump an old thread, but did you ever figure out what the problem was?

 

Fixed!

See https://www.northamericanmotoring.co...ml#post4230119 for more info!