I have the trip computer in my GL-10, and it's always done something that's a little annoying. The clock/display backlight will dim in sync with the blinkers. There must be some shared circuit somewhere, and something is dropping some voltage. Maybe a bad connection, relay, or something.

 

Anyone else notice this? Anyone try to fix this?

Try cleaning the battery connections and make sure the fusible links are making a good solid clean connection. They are in the plastic box mounted on the coolant reservoir.

I'd look at your alternator. When my car idles low in the morning, the RPMs aren't as high as they should be, and ergo the alternator is not charging as much as is could be. If I turn on the dome light, then hit the brakes, the brake lights come on and the dome light will dim.

 

However, once the engine warms up and idles normally, the alternator is charging normally. If I turn on the dome light, then hit the brakes, the dome light won't dim as much, or even at all.

 

So basically it seems like the alternator just isn't charging as much as it should be. I'm sure you already knew about this, but just throwing it out there. Not to mention that turn signals seem to take up a lot of power (my voltmeter goes up/down 2 volts or so each time the turn signal clicks). The only thing to really do is get a new alternator, preferably one that can deal with a lot more electrical demand.

 

As Cougar stated, do check the battery connections too. Corrosion can create electrical resistance (again, I'm sure you already know this), which would not allow the alternator to charge to the best of its abilities. I learned that the hard way. For 2-3 days, I thought my starter was bad because my car wouldn't start at all; it would only click. Then I decided to hit my positive battery terminal with a hammer, it knocked off some dried up acid, and my car started like normal. Good thing the starter is a pain in the behind to pull out, or else I probably would've unnecessarily spent $100 on a new one.

The Nissan Maxima alternator swap does seem to help with this, assuming your connections are clean and tight. The trip computer display lamps are two TINY incandescent bulbs. I just ordered two for mine and Subaru could still get them.

Thanks for the comments so far!

 

So I should mention that it's just the dash illumination (and not the cluster because I have digidash) that is dimming. The headlights don't dim at all. I have an EJ engine/alternator with ~50k miles so that should be fine. The battery is pretty new, no corrosion. I did check the fusable links a few months ago and they were all tight with no corrosion. Grounds are new as of a few months ago also.

 

I think I need to dig into the schematics to see what circuits are shared between these things.

 

So maybe if I ask a different way, does anyone have the trip computer that does NOT see backlight dimming (headlights on of course) with the blinker?

One of the dash fuses should provide power to the dash illumination. I suggest you check the voltage at the fuse while the problem is occurring and see if there is a voltage drop there. If there isn't a drop then move on down the line till you find it. The dash grounding could be an issue also. You may find the trouble is just due to normal wire losses.

Okay I dug down into the schematic.

 

Fuse #10 goes to the blinker. Fuse #12 goes to the instruments. They share a common supply, the black wire from the ignition switch. Bypassing one or the other to the battery eliminates the dimming. That also means it's not a ground.

 

So that means something has some resistance in the circuit back to the battery. There's no voltage drop at the fusible link (the 1.25mm link to the white wire). From there to the ign switch has about a 0.4V drop. The ign switch itself is 0.15V. The black wire from the ign switch to the fuse panel is about 0.15V. So in total the drop from the fusible link is around 0.7V when the blinker lights are on, and about 0.4V with the blinker off.

 

Most of that drop is in the white wire. I don't think the ign switch is bad with a 0.15V drop, seems ok but probably would be better with a new one; even still that wouldn't fix all the voltage drop and the dimming. I suspect it's not just my car, but that's how they all are due to the drop in the wiring. Yeah I'm kinda picky, these little things bother me.

 

So how to fix it? It seems to me the easiest way would be to tie the instrument cluster power into one of the relays going to a headlight. This would power the instrument cluster through the black/white wire and not the white wire, but still switch off/on with the ignition switch. I'm not sure how to break the connection inside the fuse box to isolate fuse #12. Basically I want to connect the supply from fuse #8 to fuse #12.

And... It was as easy at that. With a sharp side-cutters I was able to cut the bus bar between fuse #11 and #12. Then I soldered a short wire from the large black/yellow wire on fuse #8 to the now free fuse #12. No more dimming backlight with the blinker.

 

Based on my highly scientific WAG (wild-rump roast-guess) I'd say moving the current to the other circuit will be fine. It's no more than 15A (the fuse #12 rating) and the I used the headlight relay with only one 15A fuse on it (the other one has two 15A fuses). The red fusible link is good for 50A total, and the headlights would draw only 11A, the other lights max 15A, so grand total is less than 41A.

I understand what you did but by doing that you may have tied continuous power to those accessories that were on switched power through the ignition switch. I am just going by memory and don't have access to my data right now.

The headlight relay that I connected to is a load reduction relay. The relay coil is connected to the black wire going to the ignition switch. With the ignition switch off the relay opens up and the circuit goes dead.

 

See below, the black/yellow wire at B15 (middle right).

https://picasaweb.google.com/lh/photo/QFK0sj1MpAXMwQH6Oohf7-t4bszuSWzHLxcb_sc0RE0?feat=directlink

Thanks for the drawing, that helps me a lot to see how things are. You are good to go alright. I just don't like to do things like that since it can make things hard to figure out if something happens. As long as you know what is going on it is fine, but if someone else has to follow your work then that is a different case.

Yes it's always fun to figure out the PO's wiring mess! I did document the change in my car's maintenance log, so if there ever is someone after me maybe they will have a chance of figuring out what I did.

Well done!