QuestionQUESTION: Howard and all others who may help,
Because the MGB fusing architecture is poor in that there are a number of unprotected circuits, (which result in fire hazards), and because so many parts of the electrical system share a single fuse, (resulting in just one problem circuit causing all the other circuits using the same fuse to become inoperable), I would like to upgrade to an ATC/ATO fuse box, improve electric power delivery to correct levels as designed on my left hand drive, (American), MGB. I hope you can help me to replace some components and add other components.
I am not looking for a pre-made fuse box with wiring harness kit like Advance Auto-Wire due to high cost, (currently $420). I also do not want to totally rewire my MGB at this time.
I want to replace my old Lucas Fuse Box with an ATC or ATO type fuse box, improve the power delivery by adding relays to it where needed, (less wear and tear on switches), and modify wiring as needed (e.g. separate fused power source to each headlight, etc.) to accommodate these changes to improve my MGBs electrical system functions and make it safer.
It would be great to find a single fusebox with built in relays and flasher units that are geared to my MGB electrical specifications. I need a modified diagram and/or description if anyone has one showing wire runs for additions, component configurations, and electrical specifications, (e.g. available relays/fuse/wire amperage). I would like to convert to ATC/ATO type fusebox and fuses.
Surely someone has improved/resolved these Lucas shortcomings in the MGB electrical system and could help me improve mine.
I sure would appreciate any information you may have including good parts resources,(or know someone who does), as to fuse box, relays, and wiring specifications and possible a diagram I would need to accomplish this please.
Thanks,
Mike
ANSWER: Hi Mike,
While it is true the MG has several components on each of very few fuses, the MG is not noted for having troubles in this area as compared to other cars. I use to conduct seminars on import cars and an example I used (from experience) was, "A Fiat X-19 had a dozen fuses and a rat's nest of wires and every time the car would get a short it would melt the harnes down. But an MGB had only a few fuses and a few wires and would usually only pop a fuse."
I do however, think there are a few improvments that could be made. I never liked the fact that Lucas leaves purple wires unfused and I would have liked to see all the brown wires (except the alternator) on a switch on/off circuit braker. It may be a good idea to separate each headlight wire so as to possibly keep one light operational in a shorted failure.
Most of the switches and the gauge of the wire can handle the amperage load they were designed for so relays would only be an advantage if you add new loads.
Lucas has a bad reputation but from working on British cars along with German and Italian cars I see the good and bad points of each. The good points of Lucas was that the color codes of the wires were consistant between all British cars. You could open a harnes and without a diagram and tell what wire did what. The German cars were not bad either but you had no idea what color wire did what on any Fiat. You couldn't even count on two cars of the same model and year being the same and neither matched their diagram.
The switches is where Lucas fell down. Not that they couldn't handle the load, they would fall apart in use. I spent more time putting switches back together than any other electrical repair on British cars.
I think you can do most of what you want to do by just locating a better fuse box and separating some of the wires now sharing a fuse.
Let me know how it turns out.
I am building a street rod/show car out of a MGB GT and am designing my own harness. I plan to just fall short of multiplexing. Using fine ribbin wire and relays close to each load and only one heavy gauge wire. I will document the electrical part on my website. http://mg-tri-jag.net
Howard
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QUESTION: Thank you Howard! Another question.
What are the parameters for correct the fuse amperage if I put each of the 12 wires coming into the Lucas Fuse Box on a separate fuse in the ATC/ATO replacement fuse box?
About the relays, what should I use a four pole and which should I use a 5 pole connector? Will the higher capacity for most American relays be a problem?
Thanks Howard.
Mike
ANSWER: Mike, if you split the load evenly, like on the two headlights you can leave the same amp fuse, as it is not the load of a burning light that is the problem, it is a short that should blow the fuse. You just need a fuse that will burn rather than melt a wire and since you have the same size wire just keep the same amp fuse.
The only reason to use a relay is to take the amp load off of either the wire or a switch and if you are trying to take the load off of a switch, than you would need to run aditional wires, which don't make any sence to me. For what reason are you wanting to add relays? and where?
The only reason to use a 5 pin relay would be if you have two loads that you are trying to power. I can't think of any item on an MG that needs a relay. What are you adding to the car that might be too much of a load on a switch?
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QUESTION: Howard,
A very good question about my MGB's need for relays.
I am referencing "The Essential Manual MGB Electrical Systems", by Rick Astley, who elaborates on electrical problems on my left hand drive (American version) 1980 MGB and says that the American version has longer wire runs than on the right hand drive version (British). Rick Astley is very qualified and you might find this manual a good reference as well.
Testing was performed on both the left hand and right hand versions of MGBs and revealed that there was a voltage drop (due to the difference in length of wire runs and gauge(16AWG) wire in the left hand drive - American version) and the calculated relative brightness factor for the headlights (38% drop), turn signal (51% drop), and brake lights (53% drop). Rick Astley further states that "It is quite alarming both the turn signal and brake (stop) lamps work at less than half the lamps' design brightness". It is also alarming to me that the headlamp designed brightness only reaches 62% for my left hand drive MGB.
I had noticed that there was a considerable drop in headlamp brightness, especially on unlit roads, in my 1980 MGB compared to that of the other four pre 1975 MGBs I have owned before. I had been thinking, mistakenly, that the dimness was due to corroded connections I could clean up. I cleaned all connections but there was no improvement.
My thoughts about add some relays comes from Rick's manual where he discusses improving the horn circuit which also has a voltage drop resulting from the long wire run with a higher resistance by adding a relay. He states that "operating the horns by use of the relay contacts and from a much shorter power feed will reduce the possibility of any significant voltage drop and noticeably enhance their performance". In the case of my 1980 MGB set up, an additional wire is taken from the fuse block to a terminal in the relay are kept short.
So, I thought that this (adding a relay and shortening the length of long wire runs) would work for the headlight, and another might also work for turn signals, and brake light problems as well by reducing resistance drops.
What do you think Howard? Thanks.
Mike
AnswerMike, if you do in fact have 16 ga. wire then what he says may be all true and I can see the need to run a heavier gauge wire for the power and use the 16 ga. wire as a trigger for a relay. I was under the misconception that the 80 cars were 14 gauge also. If this is true I can see why you are concerned and want to make changes. Are the grounds also 16 ga.? BLM strikes again! It just proves that my thoughts were correct that BLM managment had no clue what they were doing and destroyed MG and Triumph.
You could run one 12 ga. to a front central location and one to a rear location and from that, run to each #30 pin on each relay and a short 14 ga. from each relay #87 pin to each headlight etc. Then use the existing 16 ga. original wires to go to #85 or #86 to an existing 16 ga. ground wire. (some relays had a diod in the electro magnet in #85 / #86 so there was no feedback and this made it necessary to get the 85/86 in the correct polaraity.) If you chose to run both head lights off of one relay you could use a 5 pin relay with two #87s. You may have to play electrical engineer and measure the amp draw of each light, horn, etc and get an appropreate rated relay.
I am running PC ribbin wire for my trigger wires and will only have one 12ga power wire for the front and one for the rear. My reason was so I only had one hot wire to protect and I had planned to use 3 pin relays that only had a #30, #87 and an 86. The #85 is powered off of the #30 internally so all I needed was to ground the #86 to make the contact (#30 to # 87).
I have only worked on a few 80 "Bs" and never noticed the the smaller wire. Good to know, thanks.
Howard
