Electrical...issue(?) Not really sure where to start

[konish]

Gang,

I was cruising along the other night after getting my Z (1971 240z 8/71 build date) put back together. I had just installed Speedhut gauges (volt, oil press, water temp and a remote mounted fuel gauge) and was really digging them as I drove through the night. Anyway, come up to a stoplight (as is the custom in Japan), I turned off my headlights but left my marker lights on.

When I turned the lights off, I noticed the temp gauge needle dropped almost 10*. Hmmm. So light turns green, lights go back on and the needle jumps back up 10*. I looked over at the voltmeter and it read a rock solid 14V. Just for reference, I'm running a relay headlight harness kit the PO installed...pro-looking kit

Today, I traced all the light grounds and cleaned them up, but the problem still persisted. In hopes of narrowing the problem, I turned the lights off/on, and noted the same 10* temp needle jumps so after confirming the light experiment, I turned the fan on high and the needle jumped up about 5*.

Now, I figure it isn't just a lighting issue, but an electrical load issue. Anyway, by loading the electrical system (lights, hazards, wipers, fan on high) I can get the temp to jump up by 20*. What also has me worried is that the voltmeter drops from a solid 14V and bounces between 12.5-13V (the jumping stops when the hazards are off, but it's still just a hair under 13V). Also, everything runs slower...the wipers slow way down and the fan is noticeably slower and the car runs rough.

More background...I installed the 60amp alt upgrade from MSA with the adapter plug about 8 months ago and so far everything seems to working fine. I bypassed the ammeter after installing the voltmeter. My gauges are powered by a switched 12v source (the fuel pump lead under the passenger side dash) and the gauge back-lighting is fed by on of the old bulb leads. Oh, and I have a brand-new sealed battery installed (literally yestderday).

So, here is where I'm not sure, so in no particular order:

1. Even with the electrical system loaded down, should not the 60amp alt be able to handle the load without seeing such a huge drop in voltage? I don't remember the gauges or ammeter acting that bad with the old external reg and 40 amp alt.

2. Obviously, the loading on the system is somehow causing my water temp to read incorrectly...why? Does the lower power available to the gauge (with the elect system loaded) effectively make the delta between sensor wire voltage and the sensor itself larger creating a false higher water temp reading?

3. Are the two issues related? I'm thinking yes, but I don't know a lot about electrical systems. I'm also guessing a bad internal VR...?

4. I tried adding a bunch of different grounds in the engine compartment with the same result. I tried to power the gauges from a different sources and even created a remote directly to the battery with no change. I also relocated the gauge grounds all over the inside of the car, again no change.

However, and this is where it got weird, when I made a remote ground for the gauges directly to the battery the condition REVERSED. With load on the system, the gauge dropped, and load off the gauge increased. WTF?

I'd like to get to the bottom of this so any suggestions would be greatly appreciated!

R/

Dustin

[5thhorsemann]

when you load the system and ron thr rpm up to lets say 2k, what wappens?

[konish]

When I load the system and rev the car past 2000 rpm (or any rpm for that matter), the volt meter still shows something less than 13V and the water temp reads 20* higher the entire time the load is present.

As soon as I take one electrical item offline, the volts go to over 13 volts (and in the case of turning off the lights and leaving everything else on) it'll go back to a steady 14.

I was thinking that my volt meter acts very much like my old ammeter in that the load effect on the gauge is cumulative...

My guess is that my alt VR is not working correctly...as in good on voltage but generating lower than advertised amps?

R/

D

Edited November 29, 2010 by konish

[FastWoman]

My '78 280, designed for the 60A alternator, had a rather small line (MAYbe 10 ga, protected with an 80A fusible link) from the alternator output in to the battery. Moreover, the line connected through 2 or 3 crimp junctions inside the wiring harness. There were a couple of melty/charred areas as well. All in all, the electrical path was inadequate in 1977 as it rolled off the assembly line, and it had become grossly inadequate with the ravages of time. I replaced that mess with an 8 gauge wire, to an 80A maxifuse, to the battery, with no crimps. Conservatively I might have gone with 6 gauge, but a full 60A pull seems brief enough for the 8 gauge.

Your 240 is 7 years older and was designed for a smaller alternator. You can't possibly have beefier wiring than I had in my stock 280. I would bet that's where your problem lies. Give your alternator a beefier current path to the battery, and you shouldn't see as much voltage sag.

[Zs-ondabrain]

What she said... Seriously!! Definately beef it up, minimize connections, eliminate old connctions and pathways, shorten them. Reinforce your grounds and increase your battery cable size from stock to at least 4 gauge.

I may have missed it, but how old is the battery? and what size is it? The volt meter typically shows what the Battery is doing so my guess would be that the battery is barely doing it's job.

You were in the right to move the grounds to a more stable area, such as directly to the battery but I would also back track the water temp connector in front of the motor and check all the associated connections under the dash where the engine harness comes thru the firewall.

if these items are powered off the fusebox, this may be the place to start. consider all the connections, old connections, between the battery and the fusebox, then out and thru more connectors before the power gets to the item in question. I would suggest a good cleaning of all the power related connections using Deoxit. Or even manually cleaning the terminals using small files, wire brushes etc.

I think you'll see an improvement in the regular operations after the cleaning and tightening of the terminals. Check the battery or replace it, check all power related connections in the engine compartment as well.

Good luck,

Dave

Edited November 29, 2010 by Zs-ondabrain

[konish]

Okay, isolated the alt issue to a loose belt. When revved to 2500 rpm and full elect load is introduced the volt meter read just above 13 volts solid.

If I loaded the elect system first at idle, the volts would drop to 12-12.5 V. Then upon revving the car, the volt meter stayed at 12-12.5 volts but the belt was squealing a little from the load.

I tightened the belt and the volt meter consistently reads 13 V under full load whether the the load was applied before or after the car is revved.

However, I still have the increasing water temp under electrical load issue. At this point I'm betting it's just the gauge since I was told by one of the Speedhut techs that the Speedhut Series gauges are really sensitive to ground and/or clean power...probably not as suited for duty in a 40 year old electrical system. I ordered the Revolution series gauge to see if the problem goes away as it did with my Speedhut Series vs Rev Series oil press gauge.

R/

Dustin

[FastWoman]

Well, 13V under full load at idle is probably within normal limits for that alternator. They vary quite a lot from unit to unit. You can measure your voltage drops across various conductive paths while your system is idling under load. For instance, to test the voltage drop of your alternator wire, connect the (+) side of a volt meter to your alternator's positive post and the (-) side to the (+) post of your battery. That reading will tell you how much voltage drop you're getting. Also if you can determine or guess the amperage you're passing through that wire at the time, you can compute the wattage being dissipated in the wire as heat. It will be the current times your voltage drop reading. For example, if you're pulling 40A through that wire and experience a 1V drop, you're generating 40 W of heat from that wire -- same as a 40 W light bulb, except distributed along the length of the wire (or perhaps even focused at hot spots like corroded crimp connections). Remember that the heat that is generated is trapped inside the wiring harness and doesn't dissipate very easily.

BTW, Dave is 100% correct that the voltage problems don't end there. Forty years of corrosion compromises the integrity of your entire electrical system even under the best of conditions. You could be losing voltage anywhere there's a non-soldered connection -- crimp connections, plug connectors, screw connections, fuse clips, etc. You can trace all of your voltage drops as I've described above, so you'll have some idea where the problem areas are that need to be cleaned up.