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Losing my sanity. Help with electrical.

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Losing my sanity. Help with electrical.
#1
scotty1998 Avatar
scotty1998 Scott Gibson
WATKINS Glen, NY, USA   USA
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1972 MG Midget MkIII "The VB Weller"
So I thought I was on the home stretch hooking everything behind my console back up. I noticed that three of the grounds weren't working and so tried to follow the wire loom up behind the dash. Well, I must have jostled something because now the car has no spark.

The engine turns over and the charging light comes on. The next thing in series before it hits the coil is the tachometer. It looks like power goes in and then goes out toward the coil with a white wire. If I had to guess, that's where the problem likely is? could there be anything else obvious that I'm missing? How can I troubleshoot in the engine bay by jumpering to rule out a dead coil? Simply put power direct to the coil?


1972 MG Midget MKIII "The VB Weller"
55,400 Miles
Watkins Glen, NY



Edited 1 time(s). Last edit at 2024-04-10 09:27 PM by scotty1998.

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Re: Losing my sanity. Help with electrical.
#2
Mtn Sprite Avatar
Mtn Sprite Layne M
Santa Cruz, CA, USA   USA
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1969 Austin-Healey Sprite
I believe Power goes from ign switch through the tach on the white wire. Maybe you pulled it off the ign switch when you were messing around.

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Re: Losing my sanity. Help with electrical.
#3
scotty1998 Avatar
scotty1998 Scott Gibson
WATKINS Glen, NY, USA   USA
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1972 MG Midget MkIII "The VB Weller"
Thanks for the suggestion. All pics I've seen of the ignition switch show that the leads are soldered or held down with nuts. This tells me that there's a pigtail that goes out? Does this then go to bullet comnectors? I would think that would be where the problem might be then?


1972 MG Midget MKIII "The VB Weller"
55,400 Miles
Watkins Glen, NY

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Re: Losing my sanity. Help with electrical.
#4
Mtn Sprite Avatar
Mtn Sprite Layne M
Santa Cruz, CA, USA   USA
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1969 Austin-Healey Sprite
So I'm not clear, do you have power to the Coil or not?

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Re: Losing my sanity. Help with electrical.
#5
scotty1998 Avatar
scotty1998 Scott Gibson
WATKINS Glen, NY, USA   USA
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1972 MG Midget MkIII "The VB Weller"
No power to the coil. Because the car turns over, the short has to be between the ignition switch to tach or tach to coil. I can't see any other influence here. Would you agree?

Scott


1972 MG Midget MKIII "The VB Weller"
55,400 Miles
Watkins Glen, NY

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Re: Losing my sanity. Help with electrical.
#6
Mtn Sprite Avatar
Mtn Sprite Layne M
Santa Cruz, CA, USA   USA
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1969 Austin-Healey Sprite
Sounds more like an Open than a Short.
Use your VOM.
Voltage into the Tach, voltage out of the tack?
I think it's a continuous wire from Tach to Coil so where's the break or disconnect.
Gonna have to run the circuit.
If you have bullets in that circuit the Schematic should show you I think.

12v Test light might be easier to use.



Edited 1 time(s). Last edit at 2024-04-11 09:13 AM by Mtn Sprite.

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Re: Losing my sanity. Help with electrical.
#7
scotty1998 Avatar
scotty1998 Scott Gibson
WATKINS Glen, NY, USA   USA
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1972 MG Midget MkIII "The VB Weller"
Well I looked at the back of the tach last night and didn't see any wires missing but you never can tell. That's why I was interested in your earlier comment about the feed from the ignition to the tach. Would the tach bounce around when cranking to rule this out?


1972 MG Midget MKIII "The VB Weller"
55,400 Miles
Watkins Glen, NY

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Re: Losing my sanity. Help with electrical.
#8
refisk Rick Fisk
Frankenmuth, MI, USA   USA
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If you have no power at the coil with the key in the ON position it's not a short, it's an open. The circuit is open. Trace the white wire from the switch to the coil.

In reply to # 4783640 by scotty1998 No power to the coil. Because the car turns over, the short has to be between the ignition switch to tach or tach to coil. I can't see any other influence here. Would you agree?

Scott

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Re: Losing my sanity. Help with electrical.
#9
scotty1998 Avatar
scotty1998 Scott Gibson
WATKINS Glen, NY, USA   USA
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1972 MG Midget MkIII "The VB Weller"
Yes, I agree. Regarding Layne's comment about bullet connectors, the only bullets that I see in the circuit that could affect the feed 1. from the fuse block. One goes to the fuel pump and the other goes to the ignition switch. It can't be here because the ignition and starting sequence work and you can hear the pump. 2. The other is after the ignition switch. The white leading to the tach branches to the ignition lamp (works but irrelevant) through a bullet junction. I'll check there first since that makes the most sense where the problem would be.

Then, as Layne said, it's a solid wire to the coil from the tach.


1972 MG Midget MKIII "The VB Weller"
55,400 Miles
Watkins Glen, NY



Edited 4 time(s). Last edit at 2024-04-11 09:31 AM by scotty1998.

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Re: Losing my sanity. Help with electrical.
#10
pbcjr Avatar
pbcjr peter cantamessa
east brunswick, NJ, USA   USA
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1971 MG Midget MkIII
Scott,

Just to help clarify what Rick was saying, because terminology is important when troubleshooting.
A short is when a hot/positive wire touches a ground. If that circuit is fused, a short will immediately blow the fuse. If the circuit isn't fused, a short can/will melt the insulation on that circuit's wires, and likely burn through them, possibly causing a wiring fire.
An open circuit is one where there is no connection from the power source to the end device, like from the ignition switch to the coil.
Using the correct terms helps us to help accurately troubleshoot a problem. The wrong terms can give you advice that will send you down the wrong path, wasting time and not solving the problem.

Pete


In 1974 when I was 18, I passed on buying a running and driving 1966 E-Type coupe for $1,500, which is what they were selling for at the time.
Fifty years later, I'm still kicking myself...

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Re: Losing my sanity. Help with electrical.
#11
scotty1998 Avatar
scotty1998 Scott Gibson
WATKINS Glen, NY, USA   USA
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1972 MG Midget MkIII "The VB Weller"
Understood Pete. The situation would be an open circuit. The fuse has not blown. For what it's worth, I was looking at a pic of the wiring behind the tach. Something tells me, my ignition wiring was not hooked up on mine. I don't know why but it was late last night and I was tired and frustrated. It would be great if it was that simple.


1972 MG Midget MKIII "The VB Weller"
55,400 Miles
Watkins Glen, NY



Edited 2 time(s). Last edit at 2024-04-11 09:39 AM by scotty1998.

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Re: Losing my sanity. Help with electrical.
#12
pbcjr Avatar
pbcjr peter cantamessa
east brunswick, NJ, USA   USA
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1971 MG Midget MkIII
Scott,

There was a post last year about the OP's engine cranking but not starting. He did all of the usual troubleshooting for the ignition circuit but couldn't get 12 volts at the coil.
It turned out to be a bad tach. I sold him a good one that I had and after installing it, the engine started up instantly.
So there's that possibility, too.

Pete


In 1974 when I was 18, I passed on buying a running and driving 1966 E-Type coupe for $1,500, which is what they were selling for at the time.
Fifty years later, I'm still kicking myself...



Edited 1 time(s). Last edit at 2024-04-11 09:45 AM by pbcjr.

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Re: Losing my sanity. Help with electrical.
#13
scotty1998 Avatar
scotty1998 Scott Gibson
WATKINS Glen, NY, USA   USA
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1972 MG Midget MkIII "The VB Weller"
Thanks Pete. Continuity will be my friend. I'll update the forum on my progress.


1972 MG Midget MKIII "The VB Weller"
55,400 Miles
Watkins Glen, NY

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Re: Losing my sanity. Help with electrical.
#14
Kerr Avatar
Kerr Platinum Member Norm Kerr
Ann Arbor, MI, USA   USA
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1974 MG Midget
Note that the RVC tach was adopted from July '72, so depending on the build date of your '72 it could have the later type which does NOT have the white wire go through it to the coil and there are two separate white wires from fuse #3: one to the tach, one to the coil.

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Re: Losing my sanity. Help with electrical.
#15
scotty1998 Avatar
scotty1998 Scott Gibson
WATKINS Glen, NY, USA   USA
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1972 MG Midget MkIII "The VB Weller"
My vehicle was built in March of '72. I definitely saw two white wires going into the coil connector but did not look closely enough to see whether the ignition switch connection was in place or the "power" connection. After seeing the pic of a correctly wired one, I know what to look for now.


1972 MG Midget MKIII "The VB Weller"
55,400 Miles
Watkins Glen, NY

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