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Lucas wiring issue
#1
rockyhoopple Robert Larocca
University Heights, OH, USA   USA
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Question about the Prince of Darkness Lucas electrical system.

I have been lucky so far in my 79 MGB LE

Yesterday i was starting it up and my neighbor noticed that my rear taillight was out.
I replaced the bulb, but without success.
Then I noticed that all the side marker lights as well as the taillight and parking light were not working on the driver side only. Flashers and turn signals ok.
Did a quick check and didn't find anything obvious.
Strange that it is only driver's side...
I'm thinking poor ground somewhere.
Can I just jump the ground from the pass side?

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Re: Lucas wiring issue
#2
mg rob uk Avatar
mg rob uk ROB D
OKEHAMPTON, DEVON, UK   GBR
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1972 MG MGB
suspect fuse.?

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Re: Lucas wiring issue
#3
riley1489 Avatar
riley1489 Gold Member Bruce H
Great White North, QC, Canada   CAN
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1953 Jaguar XK120
1959 Riley 1.5 "King George"
1973 MG MGB
To add ro Rob advice,
Check the Red colour wire bullet connectors under the bonnet,, (proximity to pedal box) and Red colour wire connectors in boot area RH side. The earth wires, (Black colour) should already be shared!

B


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Re: Lucas wiring issue
#4
ozieagle Avatar
ozieagle Gold Member Herb Adler
Geelong Victoria, Australia   AUS
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1958 Wolseley 1500 "Wooly"
1966 MG MGB "Bl**dy B"
1995 Toyota Highlander "Hi Ace Van"
2022 MG ZS
Hi Robert,

The two sides of the car are separately fused, so one could be faulty, or the holder is not making contact. A fault fuse may look god but be open anyway.

Here are the wiring diagrams

http://www.advanceautowire.com/mgb.pdf

Herb


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Re: Lucas wiring issue
#5
jjonns74 Avatar
jjonns74 Gold Member John Dailey
Indianapolis, IN, USA   USA
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1974 MG MGB "Athena"
1974 MG MGB "Apollo"
In reply to # 4791879 by rockyhoopple Question about the Prince of Darkness Lucas electrical system.

I have been lucky so far in my 79 MGB LE

Yesterday i was starting it up and my neighbor noticed that my rear taillight was out.
I replaced the bulb, but without success.
Then I noticed that all the side marker lights as well as the taillight and parking light were not working on the driver side only. These are all on one of the Red Circuits. Flashers and turn signals ok. These are on the Brown and Green Circuits
Did a quick check and didn't find anything obvious.
Strange that it is only driver's side...
I'm thinking poor ground somewhere. As Hazards & Turns work, it is Not a Ground problem.
Can I just jump the ground from the pass side?
Confirm 12.6vdc on all 4 Red wires at the Fuse Box

JohnD

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Re: Lucas wiring issue
#6
Not-Anumber Chris S
Southend, South east UK, UK   GBR
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1979 MG MGB GT
You havent mentioned the headlamps. Does the passenger side headlamp work ? If not then it's certainly the fusebox fuse for the passenger side lights or the wiring that leads to or from that fuse

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Re: Lucas wiring issue
#7
Wray Avatar
Wray Gold Member Wray Lemke
., SC, USA   USA
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1956 MG MGA
1958 MG Magnette ZB Varitone
1973 MG MGB
1974 MG MGB GT    & more
Chris, the headlamps aren't fused, just the tail, parking and plate lights. The right side is fed from the second fuse down, as noted above, that might be the culprit.

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Re: Lucas wiring issue
#8
Not-Anumber Chris S
Southend, South east UK, UK   GBR
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1979 MG MGB GT
Thanks Wray, I'd not realised that before, Scary really that the headlamps are not protected by a fuse.

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Re: Lucas wiring issue
#9
Wray Avatar
Wray Gold Member Wray Lemke
., SC, USA   USA
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1956 MG MGA
1958 MG Magnette ZB Varitone
1973 MG MGB
1974 MG MGB GT    & more
Chris, the original, popular rationale was that if they were fused you could lose both headlights leading to a dangerous situation at night. I think most modern wiring systems run the headlights through relays and are protected by fuses. There are plenty of differing opinions about the topic.

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