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Re: Do NOT fuse headlight circuits!!!!

To:, mgs@Autox.Team.Net
Subject: Re: Do NOT fuse headlight circuits!!!!
Date: Mon, 30 Jun 97 14:16:19 EST
     I'm the one that started all this with my wiring questions.  Anyway, I 
     got a lot of valuable information from the list and greatly appreciate 
     everyone's help.
     I had a '76 Midget when I was in college.  One summer evening I was 
     headed south in the left lane on I-95, about an hour north of Boston. 
     I went over a pretty wide seam (construction? heat expansion joint?) 
     in the pavement at about 65 mph.  Next thing I know, all dash lights, 
     marker lights, and tail lights were out.  ALL I had was Headlights.  
     Cross-lane dive to the next exit (common maneuver in Massachusetts) 
     and to a service station.  A fuse had gone out, if I recall.
     Guess it was good for me that the headlights stayed on, but I was a 
     little nervous in that little car with no lights to warn semis of 
     where I was. . .
     77 B (rewired yesterday and on the road again)

______________________________ Reply Separator _________________________________
Subject: Do NOT fuse headlight circuits!!!!
Author: at Internet
Date:    6/30/97 1:14 PM

In a message dated 97-06-30 10:06:17 EDT, (Mark 
Moburg) writes:
> The best suggestion I've seen here is to run your headlights (high and low 
>  beams) through relays.  You can buy relays inexpensively at any auto parts 
>  store.  Use heavy-gauge wiring from the hot lead of your battery, WITH AN 
>  IN-LINE FUSE(!) close to the battery, and use the wiring from the switch 
>  switch the relay.  This will save the factory harness much stress, and may 
>  make your lights a little brighter, since those poor electrons won't have 
>  much Lucas to struggle through.
NO, NO, NO, A THOUSAND TIMES, NO!!!  Do Not fuse the headlight circuits! 
Headlight circuits are not fused for a good reason. Believe it or not, not 
having fuses is a safety feature! Given your choice, which would you prefer - 
standing by the roadside and watching your car burn to the ground, or having 
the headlights go out all of a sudden as you are driving on a winding back 
road at 65 mph on a black, moonless night?
Modern automobiles use circuit breakers in some cases for the headlight 
circuit. Quite often, as wires fray, they initially make contact with ground 
only under certain conditions, such as accelerating, stopping, right turn, 
etc. As this happens, the lights will flicker, reminding you to get them 
fixed. With a fuse, even a momentary short circuit will blow the fuse and 
kill the lights. With a circuit breaker, it takes a little longer, and after 
a brief cooling off period, the lights will come back on. A brief short as 
described will not kill the lights. Of course, if you get a dead short, you 
lose the lights no matter what. There is nothing that can protect against 
this. The only line of defense is to maintain the wiring in excellent 
If you must use fuses, at least put a seperate fuse on each side, so that 
only one light will go out. If you do this, it becomes IMPERATIVE that you 
replace a headlamp that goes out immediately! You don't want the good side to 
be the one that fails on that night drive through the mountains.
Below is a quote recieved from Ross MacPherson, in a response to my post on 
this same subject earlier:
"1972 Mazda B1800 Pickup truck.  First and LAST japanese vehicle I will ever 
own.  It did this very thing to me at the curve in a backroad through a corn 
field in the middle of the night. VERY SCARY! Frayed wire at a side marker 
took out the fuse for ALL running and headlights at once."
Strong testimonial, I think.
Dan Masters,
Alcoa, TN
'71 TR6---------3000mile/year driver, fully restored
'71 TR6---------undergoing full restoration and Ford 5.0 V8 insertion - see:
'74 MGBGT---3000mile/year driver, original condition 
'68 MGBGT---organ donor for the '74

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