Intermittent HUD/Dash Lights/Climate Lights! Help!

[Klot]

(technical enough for technical discussion section?)

Hey guys,
FINALLY got a 240sx! Glad to finally own one of these cars. I've searched for this issue, and have found results but I have it slightly different than I could find. Don't be afraid to be technical, I'm ASE certified for electrical systems.

The dash lights/digital speedo (HUD)/climate control lights are possessed. The tach works, the fuel and temp gauges work and the warning lights for seatbelts/BRAKE/check engine/etc all work, but the lights that illuminate the dash don't work along with the HUD and climate control lights. HOWEVER, this changes day to day... Sometimes when I turn the lights on, the lights for the dash come on along with the HUD like they should, but within 10 seconds the HUD fades out but the dash lights stay on. When the lights DO come on, the dimmer switch doesn't dim them - it stays at 100% brightness. Yesterday when I hit a bump (lowering springs are firm) the HUD popped back on for about 10 seconds again and it read the same speed my GPS speedo on my phone read, so I know vehicle speed sensor works and is good.

The owner before me installed little LED light strips for illumination to the 240sx clear plastic above the radio, I haven't checked what circuit they're spliced into, but I don't think two LED light strips (about 6 LEDs on each) would pull enough current to make the fuse blow so I'm not too concerned about them.

Sum up! What is possessed:
-dash illumination lights (comes in/out)
-HUD digital speedo (comes on when dash lights work, but fades out in 10 seconds)
-climate control illumination lights
-dimmer switch

What I have read:
1) the TCU is a huge problem, so it could just be that since I have an odd set of intermittent issues.
2) if none of the gauges, accessories, and dash lights work it could be the alt (alternator?) fuse... but my tach, fuel, and temp gauges all work.
3) if none of your dash lights and tail lights work then its the rear lights fuse... but my rear tail lights work.
4) if new fuse blows for dash lights, unplug dimmer switch and replace fuse again (shows if dimmer switch is the issue)
5) pull out radio w/harness, check condition of wires (look for exposed wiring that could cause a short)
6) for the HUD, the circuit board for the HUD could be out? But how would that be possible if it comes on then goes out?

Quite an odd set of problems I know... any help is appreciated!

[daemonyk]

That really sounds like a timing control unit problem or a problem with the wiring on that circuit. All of those systems are tied into that box, and problems with that box would cause all of those systems to fail at the same time. Often times what happens is a solder point inside the box weakens, and causes the problem to happen at varying frequencies. It's something that goes bad on 240's over time ANYways, and tampering with the electricals in that area can make it worse faster. So if the previous owner DID tamper into that circuit, maybe wired in a short, who knows, but problems with exactly and only those lights / systems tells me it's on the TCU circuit.

The box can be bypassed, and that usually fixes it, but you can no longer dim the instrument lights. However, it sounds like that's already the case I've also seen articles that tell / show how to locate and re-solder the weak point. IIRC, the inside of the TCU is not a very sophisticated PCB, and can easily be worked on. In fact...

http://www.nicoclub.com/archives/fix-fo ... ights.html

Check that out

And check for any shorts alterations or discrepancies on the wiring for that circuit. Rule out bad wiring / shorts / grounds / loose connections / etc.

G'luck

[Klot]

That really sounds like a timing control unit problem or a problem with the wiring on that circuit. All of those systems are tied into that box, and problems with that box would cause all of those systems to fail at the same time. Often times what happens is a solder point inside the box weakens, and causes the problem to happen at varying frequencies. It's something that goes bad on 240's over time ANYways, and tampering with the electricals in that area can make it worse faster. So if the previous owner DID tamper into that circuit, maybe wired in a short, who knows, but problems with exactly and only those lights / systems tells me it's on the TCU circuit.

The box can be bypassed, and that usually fixes it, but you can no longer dim the instrument lights. However, it sounds like that's already the case I've also seen articles that tell / show how to locate and re-solder the weak point. IIRC, the inside of the TCU is not a very sophisticated PCB, and can easily be worked on. In fact...

http://www.nicoclub.com/archives/fix-fo ... ights.html

Check that out

And check for any shorts alterations or discrepancies on the wiring for that circuit. Rule out bad wiring / shorts / grounds / loose connections / etc.

G'luck

I've already got that page bookmarked, haha. I'll give you guys an update on whats wrong this afternoon when I get some things pulled and I check out the wiring more in-depth!