Instrument Light Problems

[z3beemer]

Been searching the forum for answers to my problems but have been unable to find one.  73 240Z complete tear down and rebuild. Working on reinstalling the dash and electrical.  Trying to check out as much as possible before moving on. I've connected a motorcycle battery to the main electrical cable in the engine bay (that normally connects to the battery cable) for testing purposes.  I did a pretty good job of marking all wires and plugs to facilitate reconnecting.  Also I installed a new ac/heater system that had its own wire harness.  I only had to use one 12V switched wire from the original harness and the blower motor control switch. So now I have two current problems.  Most all the instrument lights work but they come on as soon as the ignition is turned on.  The switch on the multipurpose switch has no effect on the instrument lights.  The rheostat does control the intensity.  The second problem is that the 3 instrument lights on the heater control panel do not work at all (bulbs are good).  I'm wondering if the multifunction switch is bad.  I bought this as a project car that ran but never paid any attention to the instrument lights. All other electrical devices worked.  If it's the multifunction switch, I'll replace it, but I know they are pricey, so I don't want to spend the money and have the same problem.  I suppose I could splice into one of the other instrument wires and run power to the heater control panel lights, but I will still have the problem with the instrument lights not being controlled by the light switch.   This originally was an automatic trans being converted to manual shift (not sure that has anything to do with it but I'm stumped). Thanks in advance for your assistance.

Paul (z3beemer)

[Racer X]

Do you have everything connected as it will be when the car is finished, including all grounds?

It is possible that the system is back feeding if parts of it aren’t fully connected and grounded.

 

[SteveJ]

I suspect something is cross-connected, possibly in the center stack.

1. If you unplug the 9 pin connector on the combo switch, does that affect the lights?
2. Are you looking closely at the BE section of the FSM to see if you have the connections correct? 
3. Does it look like a previous owner hacked the wiring?

[z3beemer]

Went another round with the instrument lights and lost again.  To respond to a few of the suggestions / questions above: I unplugged the 9 pin connector on the combo switch....No affect. Instrument lights stayed lite.  The car is not in finished mode.  I'm trying to verify as many circuits as possible now, so I don't have to tear everything apart after it is all back to together. I checked all my connections they all seem ok. I marked each wire on both ends as I took it apart.  On the right kick pad where all the plugs and relays are there are two large blue male/female plugs.  They are interchangeable (physically but maybe not electrically) I noticed the wires colors on the male side did not match the female side, so I switched them.  Now the wires match.  I thought " yes, that was the problem"...it wasn't.  I looked at FSM BE section and for the meters (gauges) there is a simplified electrical drawing for illumination.  It shows the lamps in parallel connected to a 12v source (battery) then thru the rheostat.  No other switches are in the circuit.  Could it be that there is power to the instrument lights any time the key is on and they are turn off via the rheostat????  As for the original wiring, the car originally had an ARA dealer installed A/C system and an aftermarket alarm.  Several tie ins were made but only to bring power to the units.  All that has been removed.  I don't believe any of that is causing my problem.   As usual you input is greatly appreciated.

z3beemer

[SteveJ]

No, the rheostat ONLY controls brightness. The instrument lights go through the parking light circuit. They light up when you turn on your parking lights. For that matter, are your front/side/rear marker lights on when you're doing this test?

Here is how the factory circuit is wired:

1. Power comes off the 20A fuse through a green/blue wire.
2. The wire goes to the combo switch. When you turn on the parking lights, it is connected to a green/white wire.
3. The green/white wire runs out to all of the front/side/rear markers. It also goes to the rheostat.
4. Power comes out of the rheostat through the red/blue wire and goes to the gauges. The gauges are all grounded for the return path.

From this, I am guessing you have cross-connected something between the dash and body harness, possibly in this area:

If not there, maybe you cross connected something in the engine bay, though I'm not sure what. Of course, if a previous owner hacked the wiring, that makes it more of a challenge to find the problem.

Note: The connectors between the engine harness and body harness are color coded. Make sure the colors match.

Edited November 17, 2022 by SteveJ

[Racer X]

I still think that since the entire system isn’t fully connected and grounded the lights are back feeding somewhere.

[z3beemer]

You may be right RacerX.  In the past I found many times when you're having light problems it ends up being the grounds. Been thru it again today everything seems to be correct, but I could have mis marked something on disassembly, but I was pretty careful and only disconnected one wire/plug at a time and marked both sides of each wire. Does anyone know where I can get a large print color wiring schematic?  The one in the FSM is next to impossible to follow. Thanks for all your input guys, I really appreciate it.  I'll keep fightiing it.

[SteveJ]

2 hours ago, z3beemer said:

You may be right RacerX.  In the past I found many times when you're having light problems it ends up being the grounds. Been thru it again today everything seems to be correct, but I could have mis marked something on disassembly, but I was pretty careful and only disconnected one wire/plug at a time and marked both sides of each wire. Does anyone know where I can get a large print color wiring schematic?  The one in the FSM is next to impossible to follow. Thanks for all your input guys, I really appreciate it.  I'll keep fightiing it.

If it was backfeeding, it would have to be through the turn signals or brake lights or your dash isn't grounded. Those are the circuits where backfeeding could occur. 

1. As I asked before, are the side markers coming on when the gauge lights are on? 
2. Are any of the indicators/warnings coming on with the gauge lights (high beam indicator, turn signal indicator, brake light warning)?
3. What happens if the AC fuse is pulled? (The fuse marked 1 below) Do the gauge lights come on?
4. Do you have brake lights? Turn signals (with ignition on, of course)?
5. Do you have voltage on each side of the Park Tail fuse (Marked 2 below) with the ignition off?
6. What is the resistance between the dash frame and the chassis? 
7. What is the resistance between the dash frame and the negative terminal on the battery?

[z3beemer]

Thanks Steve.  I'll check out the items you mentioned on my next go around. I need to walk away from it for a day or so. I'll let you know what I find. 

[z3beemer]

Steve thanks so much for all you help so far.  Once I get this resolved I'll have to send you a case of beer or something.  Spent several days chasing the demons and here's  what I've found:  I found the reason the instrument lights wouldn't go out.  Looks like I connected the plug to the radio, which was a key on power source, to a matching plug on the instrument wiring. So it was supplying power to all the instrument lights all the time. However now I do not have instrument lights at all.  Here are some of the things I have and do not have: Ground between dash and chassis .5 ohms.  Between dash and negative batter terminal -99 ohms.  Never saw a negative ohm reading before but maybe it's because I have the negative of the battery connected to the chassis via a jumper cable, since there is no engine in the car.  I do have dome light and glove box light and switches work as should(door push button switches and glove box switch).  Brake lights work normally. Back up lights work if I connect the leads together (no trans installed yet).  Headlights are not installed but have power going to the pigtails when switched on.  High beam indicator works as normal. No trail lights, marker lights, turn signals or instrument lights.  With the hazard switch turned on (pulled out) tail lights flash, turn signals flash and turn signal indicators on dash all flash (but not the marker lights). I seperated the 9 pin connector on the steering column and checked power under 3 conditions; key off, key on light switch off, and key on and light switch on. I can supply those results if you think it would be helpful.  I think the most telling thing I found is the there is no power to either side of the 20A fuse labeled Flasher.  I'm not sure where the power to it comes from, why its not getting there or if this will solve my problem. One other thing; none of the pigtails between the wiring harness and the center consol are connected at this time.  I don't think this is the problem since most of what's under there are indicator lights. Your thoughts???

[SteveJ]

Disconnect the 9-pin connector on the steering column and take photos of it, especially where the pins are. If the 9 pin connector is disconnected, you won't ever have a complete circuit for the parking lights/gauges.

Take the cover off the fuse box, and take a clear photo of the fuse box. Also, did you check for voltage at the parking light fuse (the one I marked as #2 above)? What are the results? The fuse should have voltage to ground on both sides even with the key off.

In order to do the diagnostics properly, we have to go through the circuit carefully. 

Since there is not an engine in the car, could you share a picture of how you have the positive battery terminal connected to the wiring harness? Normally, the positive terminal is connected to the starter, and a fusible link is attached to the same terminal on the starter, going to the white wire.

[Racer X]

17 hours ago, z3beemer said:

 Here are some of the things I have and do not have: Ground between dash and chassis .5 ohms.  Between dash and negative batter terminal -99 ohms.  Never saw a negative ohm reading before but maybe it's because I have the negative of the battery connected to the chassis via a jumper cable, since there is no engine in the car.  

When measuring resistance there isn’t any polarity. You either get an ohm reading or you don’t. If the reading is a negative value something isn’t right. 
 

Try the measurement again, ensuring good contact of both probes.