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question on electrical gauge wiring

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77MidgetMkIV

77MidgetMkIV

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Hello all,

I am trying to track down a problem in my system that is knocking out my tach, fuel gauges as well as turn signals and wipers. On advice from here, I have checked every connection in the fascia wiring harness, I have cleaned the fuse block and cleaned all grounding points that I could find on the vehicle. I am now thinking that it might be the voltage regulator, but am not sure how to test the unit. According to the wiring diagram, the double lead connecting to the V.R. goes to the fuse block and the hand brake switch, and the single lead goes to the fuel gauge. Questions:
1. Am I correct, then, in assuming that all of these accessories are wired in series (still not that good in reading the diagram) meaning that the problem could be anywhere?
2. What is the best way to test the V.R.?
3. Any other points/connections/hints? Other than a couple orphaned wires for a now gone stereo system, everything seems to be original, and the only connection that seemed suspect was a slightly damaged brown wire listed as part of the ignition system in one of the connectors under/behind the steering wheel, but the ignition circuit functions fine.

any advice/thoughts would be appreciated, as I am far far far from being considered a wiring guru.

thx
markfitz
 
The voltage stabilizer (when examined very closely) should have two marked contacts "B" and "I". The "B" terminal goes to the Battery and the "I" terminal goes to the instruments. The "I" terminal voltage is supposed to be at 10V, but it's not possible to measure this accurately with most volt meters as the signal is really an average of "off" and "on" 12v pulses. Make sure there is power on the "B" terminal before you worry about testing the output of the voltage stabilizer. (BTW, the case of the stabilizer must have a good ground connection or it will not work properly... and will pass a full 12v all the time).

The tach should not be fed from the stabilizer. Tachs typically get a switched 12v supply, not 10v. The fuel and temperature gauges only need a ground connection for their lamps. To get a reading, these gauges pass current from the voltage stabilizer to ground through variable resistance inside their sending units.

It sounds like you're loosing power to so many things that the problem is likely on the switched power, not the ground connections. I wish I could tell you what specific points to check. However, I'm afraid that you're just going to have to sit down with a wiring diagram and volt meter tracing through the supply circuit to see where you're loosing voltage.
 
Thx Doug. Not exactly what I was hoping for, but I now know a little more than I did previously. One thing I did not mention was that the problem was intermittant for a long time, and now seems to be permanent. When poking around last night, I was able to get the fuel gauge to register briefly, then it died again. At the time, I was poking at the V.R. That is why I thought it might be that.
 
Re: question on electrical gauge wiring:progress??

Well, I started the attack with the multimeter, and found something interesting, and yet unexplainable. I first checked the resistance over each fuse circuit on the fuse block, and fuse #2, which is the fuse that supplies the gauges, as far as I can tell from my diagrams and "on site" exploring, showed high resistance, while the others showed none, meaning that they were allowing current to flow fine. Bear in mind that I had cleaned all the terminals on the fuse block last night....anyway, I switched fuses 2 and 3 to see if the problem followed the fuse, and now they both are at zero!!! I took the block out again, and it looks clean. I turned the accessories on, and guess what is working???? you guessed it- EVERYTHING!!!

Well, I am going to throw the seats back in, since I removed them for easier access to the fascia harness, and put the console back in, and take it for a drive, and see if everything stays on ::crosses fingers::

I will keep updating.
 
Re: question on electrical gauge wiring:progress??

Sounds like that fuse wasn't seated good or the terminal block is corroded on the back side. You might get away with what is done already or you might have to take the fuse block out and resolder the connections on the block. Hopefully you have it resolved but I've found that things don't often "fix themselves"...
FWIW which may be very little...lol
JC
 
Re: question on electrical gauge wiring:progress??

Well, I think it was more of re-seating the fuses that did it. Boy, do I wish these things fixed themselves!!!!

I know that they were fully seated when I reinstalled them, but I am thinking that there may have been a little gunk that released when I swapped the fuses. Also, the back of my fuse block is not soldered, it is rivited. I am going to take it apart again and see if I can concoct a solution clean it better, as I used sandpaper and emory boards before.
 
Re: question on electrical gauge wiring:progress??

Automotive electrical gremlins can be very vexing. Many years ago I owned an early Toyota Celica. One day while driving I moved the turn signal lever to indicate a right turn and the horn started going off (weakly) each time the lamps were supposed to flash. I checked everything I could think of and finally in desperation changed the fuse. New fuse and everything was fine. I carefully checked the old fuse and found the metal filament inside had a hairline crack right across the middle. It looked intact but had actually failed. Somehow the current for the flashers found a path to ground through the horn circuit... go figure.

I'm glad that you found your problem at the fuse block. I hope you figure out a way to keep it from happening again.
 
Re: question on electrical gauge wiring:progress??

thx JC and DK. I am heading back to the gremlin wars in a bit once I finish painting my living room (working vacation, so to speak)...17' ceilings look great until you have to paint the room!!!
 
Re: question on electrical gauge wiring:Culprit!!!

Well, I finished up painting the 2nd and last coat, and headed right out to the car to prep it for a sticker. When checking my lights, I noticed that the front right and rear left running lights were not working. Ugh!!! My first thought was that I had disturbed some new gremlin. Then I consulted my trusty wiring schematic- they are connected to fuse #3.....wait a tick...that is the one that I swapped #2 with to fix the gauges!!! Turns out to be a semi-bad fuse, in that it sometimes works and sometimes does not- that is why when I have checked them in the past, I have done so only visually, and they have been ok. The fuse appears good, and even passes a resistance test...sometimes. I was able to get it to fail by shaking it a lot and then testing it.

Well, I now know a lot more about my electical system and my gauges, and all my harness connectors and grounds are cleaned and checked, so it was definitely not a waste of effort in ripping everything out for this little beastie of a problem. I am off to NAPA to get some fuses, and then hopefully to the garage to get an inspection sticker.
 
Re: question on electrical gauge wiring:prologue

Well, I have come to the end of this little repair journey. I returned from NAPA and installed some new 25A fuses (the ones that were in there were 35, and that made me a little nervous), and everything is operating perfect!!!! I took it down to the garage for an inspection sticker right after. Now, I must admit that I went to a place ikn town that is notorious for "lenient" inspections......oops! Turns out that they had been written up for said easy inpections, and they threw the book at me, right down to actually measuring tire tread, and high and low beam high and spread, not eye-balling them, but measuring them. He complained a little about the drivers' side headlights being lower than thte passenger side, and I told him that if he found an MG midget that didn't list to one side or the other, to let me know. He actually laughed. In the end, I received a sticker, and I am now completely legal to wander the highways and bi-ways. Just got back from putting 50 miles on it through central MA farm country, with a quick stop at my preferred pub....ahhh.........it's sweet for a couple reasons: 1)for the first time in 2 years, I am driving the midget with a legal inspection sticker, and 2) I did all the work myself, from electrical to mechanical to tuning to...well, you know.

Very satisfying. I am not touching a $($&#(&^#@ thing on this car until it goes away for the winter, when it receives new rear springs, and new suspension bushings all around.

I know this is repetitive, but many thanks to all on BCF who have helped me in the last 8 months while I tackled all these refits. I can honestly say that I would not have been able to do it without you.


see you on the road!
mark
 
Re: question on electrical gauge wiring:prologue

I can't help be be a little /ubbthreads/images/graemlins/cryin.gif with envy!!! LOL.

I'm dying to get my car back from paint so I can begin putting it back together. What's really bad is the temperature has finally dropped to below 100 during the daytime. It's been perfect driving weather and I don't have my midget on the road yet. /ubbthreads/images/graemlins/frown.gif But, on the flip side, when you put your car up for the winter, I'll still be happily /ubbthreads/images/graemlins/driving.gif mine, hopefully every day!

Glad to hear your car is running fine and you're enjoying it. /ubbthreads/images/graemlins/thumbsup.gif
 
Re: question on electrical gauge wiring:prologue

One of the things I have found very helpful on my "rust-bucket" daily driver,a somewhat modified 59 Sprite,in terms of electrical problems is (since I work in the marine industry)a HD electrical contact spray cleaner & protector by CRC. Once electrical connections have been properly cleaned and then sprayed they will give improved service,even in moisture-prone British electrical systems!
 
Re: question on electrical gauge wiring:prologue

P.s. Good grounds (P or N) are always very important!
 
Re: question on electrical gauge wiring:prologue

If you are going to be doing the rear springs and bushings, start spraying PB Blaster or other penetrating oil on them now! Then reapply often until you are ready to do the work.
 
Re: question on electrical gauge wiring:prologue

Way ahead of you, Mike- thx for the advice, though, and reminder to others. Yeah, I started that while I had it up on jack stands. Usually, it is back on the stands once a weekend, so I try to hit everything. Actually just got back from filling up the tank, and now I am off again for a little driving before the Red Sox/Royals game is on.
 
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