Intermittent Dash Lights (possible TCU related)

Post by **octothorpe** » Mon Jan 11, 2010 9:51 am

I have a 1992 KA24de with digital dash. Recently, my dashboard lights have been giving me some grief. When i first start my vehicle with the outside temperature below 50°, my dashboard illumination will not come on. After driving about 20 minutes or so, it will suddenly begin to work and will continue to work until i park for the night. I assume that something needs to warm up, but am not entirely sure. I do have a copy of the FSM and have performed the diagnostics on the pins for the TCU and all seems fine. I've also popped the top to see if there are any burned out traces and this also looks fine. A voltmeter between ground and the red/yellow-striped wire from the wiring bundle indicates that the dimmer switch is working correctly. Although this shouldn't be a huge problem, i go to work at 0dark:30 and i have no speedometer indication and, more importantly, the odometer will not register until the illumination comes up. Is there anything, other than a $350 TCU that i should be looking at? Also, is there any place to order a TCU other than a dealer?

Thanks in advance for any help,#

Post by **esd51918** » Wed Jan 13, 2010 5:49 pm

By your description I assume the only lights you are experiencing a problem with are the instrument cluster lights. Are the climate control, radio, gear indicator (if it's an automatic), and ash tray lights working OK? I have an '89 SX with a similar problem. The climate control lights, etc. work OK. The instrument cluster lights don't work unless I run a jumper from the ground screw on the back of the cluster to the chassis. However, when connected that way the dimmer switch will dim the climate control lights but not the cluster lights. In the FSM for the '89 on page EL-52 it shows that the cluster lights and the climate control lights, etc. are grounded at different locations. I'm still chasing this rabbit but I think the problem is related to the ground for the cluster light circuit.

Post by **octothorpe** » Thu Jan 14, 2010 3:37 pm

eds51918,Thanks for the info; the symptoms i'm experiencing are exactly as you describe. I didn't consider the ground issue as, after the car warms up, the dash lights would come on. I never actually mess with the dimmer, so it doesn't bother me not having dimmer capability, i just want the speedo/odometer to work. The pain is that i have to, once again, rip my dash apart. Still, if it gets me back to 100%, it'll be well worth it. And it keeps me from wasting $350 on a TCU or digging through the local pick-a-part to try to locate one.

Thanks again, you've been most helpful!#

Post by **esd51918** » Thu Jan 14, 2010 4:29 pm

Octo,If your '92 is like my '89 the ground for the instrument cluster is located to the right of the glove compartment above the ECU. I haven't tried to access the ground yet, but I think you have to remove the glove compartment to get at it. If you try it before I do please post how you went about it. My speedometer & odometer aren't working either. Good luck.

Post by **octothorpe** » Mon Jan 18, 2010 11:49 am

esd51918,Well, good news and bad news: I did get the illumination working again, as well as the odometer; but it wasn't a simple grounding issue. After digging around a bit more on the site, i came across this post: http://www.nicoclub.com/articles.php?id=158878 which points to a 50v, 1µf capacitor located in the HUD as the culprit. Although the fix is inexpensive, it is tedious. Fixing the HUD also fixed the issue with the odometer as they are connected with a jumper. By the way, polarity does not appear to be an issue as the only capacitor that i could find was non-polarized and everything works fine.

From your previous posts, you mention that you have no illumination (or speedo/odo), but don't mention whether this is 100% of the time or not. My problem only manifested itself when it was cool outside and returned to normal after the vehicle (and the dash) warmed up. This is specifically mentioned in the fix. If you have no illumination regardless of cabin temperature, this may not be the fix for you. That said, it's definitely worth a look. Also, did your speedo/odometer work after you applied the chassis ground?

To Aaron Longenecker,I don't know what possessed you to think of laying a soldering iron on a capacitor when troubleshooting this issue, but i humbly bow before your tech-fu! Your skills are as brilliant as they are audacious!

Many thanks,#

Post by **esd51918** » Mon Jan 18, 2010 6:52 pm

Octo,I am familiar with Mr. Longenecker's post on how to test the capacitor in the speedometer unit. I tried testing the capacitor as he describes but the digital display never came to life for me. His directions are pretty clear so I think I did it right. I take it that you tested the capacitor as he describes, the display came up, and you then suceeded in replacing the capacitor.

On my vehicle the HUD, digital speedometer, odometer, and cluster illumination lights did not work. I got the idea for running the ground from this thread " TARGET="_blank">zerothread/304006 , specifically the post dated 04/30/08 from danielsan. When I attach the ground the cluster lights work, but can't be dimmed. However, the dimmer switch will dim the climate control lights, etc. Even with the ground attached the HUD, digital speedometer, and odometer still don't work. Cabin temperature or ambient doesn't make any difference. They just don't work. I've spoken to a Nissan mechanic whose had experience with these speedometers. He said when they get like this you generally have to replace the digital unit. Glad you got yours working.