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Midget 1500 (78-79), Embarrassing story+ Wire question

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MgMig1979 Avatar
MgMig1979 Mike E
Philadelphia, USA   USA
Model: 1978--1979 MG Midget 1500


This is a very embarrassing story. In my quest to get this car running, I created one more problem . . .


I’m converting from OEM 45DE distributor with Ballast resistor (BR) to a non-ballasted 25D with points.
Long story, made short—I managed to reuse a wire from the BR and ended up "cooking" this white wire.


I apologize for my poor knowledge of electrical systems. (I've included pictures below to illustrate what I am trying to say below)

This white wire originally goes from one side of the ballast resistor, into a the harness, to a 5 pin connector with Male ends. Here, the white ballast line meets a white line second line. these connect to a female white line that does behind the steering wheel.


I have several questions

1. What gauge wire will I need? Or, where can I go to find out exactly?

2. What damage should i expect when I get behind the steering wheel?

I haven't gotten behind there and seen if I will be replacing this line, or what it connects to.

3. what is the best way to get behind the steering wheel?

4. Any tips on re-wrapping the sections of harness? looks like it takes a skill i probably don't have


Has anyone done something similar to this? I appreciate ideas, suggestions, or stories.


Thank you all for your time, I am learning a hell of a lot here

- Mike

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after cooked wire 1.jpg    45.9 KB
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dickmoritz Avatar
dickmoritz Platinum Member Dick Moritz
Philly 'burbs, PA, USA   USA
The key to your question is your ignition coil. If it is original, then it would have a resistance of about 1.5 ohms from coil + to coil -. You can check this easily with a simple ohmmeter.

Assuming the coil is original, then coil + would have received full battery voltage during cranking and, with only 1.5 ohms in the coil, and engine startup would be easier. Once the engine is running and the key is relaxed from the Crank position to the Run position, then power would have been fed to coil + through the ballast wire, which would have an additional 1.5 ohms built into this resistor. This would provide a full 3 ohms during running, which is what most 12 volt coil-ignited engines like.

So one option would be to test the wiring to see if an existing wire in the harness has continuity/power only when the key is in the Crank position. If this wire is still intact, then you can connect it to coil + to supply full B+ when cranking. Then you can check to see if there is a wire that has power in the Run position. This would be the original resistor wire and would be compatible with your coil, since 1.5 ohms + 1.5 ohms yields the preferred 3.0 ohms.

Or, if you prefer a simpler setup, you can simply buy an ignition coil that measures 3 ohms from coil + to coil - and wire it so that it gets full B+ while cranking and while running...

Dick



Errabundi Saepe, Semper Certi
(Often wrong, but always certain)

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MgMig1979 Avatar
MgMig1979 Mike E
Philadelphia, USA   USA
Dick,


Thank you for your quick response.

Unfortunately, I should specify that I did upgrade the coil. A 3 Ohm Bosch, I believe.

basically, the new set-up called for a new wire to connect to the fuse box to the "+" Side of the coil, then a wire from the "-" side of the coil to the distributor.

The power and tachometer lines were suppose to remain , but the green and white wires from "+" side of the original coin were not meant to be reused.

I carelessly hooked up one of the white lines (meant to carry 1.5 ohms (?)—as you stated) to the plus side . . . which resulted in this line being fried all the way to behind the steering wheel


I hope this makes sense! my apologies

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dickmoritz Avatar
dickmoritz Platinum Member Dick Moritz
Philly 'burbs, PA, USA   USA
No worries, Mike. Just isolate and insulate the wires that fried, including the original wires that went to your coil, and wire your 3 ohm coil so that it receives a full 12 volts B+ when cranking, and a full 12 volts B+ when the key is in the Run position. With a 3 ohm coil you don't need any kind of resistor at all. Note that, in our cars, white wires have B+ all the time the key is on, and the white circuit is not fused. So the white circuit is a good place from which to source power to coil +... Just double-check to be sure you have B+ there when cranking and also when the key is in the Run position... Just re-connect the tachometer wire to its original position on the coil...

Dick




In reply to # 3892766 by MgMig1979 Dick,


Thank you for your quick response.

Unfortunately, I should specify that I did upgrade the coil. A 3 Ohm Bosch, I believe.

basically, the new set-up called for a new wire to connect to the fuse box to the "+" Side of the coil, then a wire from the "-" side of the coil to the distributor.

The power and tachometer lines were suppose to remain , but the green and white wires from "+" side of the original coin were not meant to be reused.

I carelessly hooked up one of the white lines (meant to carry 1.5 ohms (?)—as you stated) to the plus side . . . which resulted in this line being fried all the way to behind the steering wheel


I hope this makes sense! my apologies



Errabundi Saepe, Semper Certi
(Often wrong, but always certain)

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jmac Avatar
jmac Platinum AdvertiserAdvertiser Jere McSparran
Greenup, IL, USA   USA
1971 MG Midget "Joy Ride"
1978 MG Midget "Therapy"
1978 MG Midget "(SOLD)"
Good explanation Dick!



JMac
JMAC Engine Shop
http://www.jmacengineshop.com


Member Services:
Midget/Spitfire 1500 engine rebuilding.
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MgMig1979 Avatar
MgMig1979 Mike E
Philadelphia, USA   USA
Dick

My sincerest apologies for the late reply—had to bench the project for a bit, but back at it. I agree with Jmac, you explained my question very well. I really appreciate it!


-Mike

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