Headlight Question

Janet & Jeff Curtin · Post by **Janet & Jeff Curtin** » Sat Sep 18, 2004 3:39 pm

Can anyone advise just how high a wattage on bulbs you can go without
worrying about getting a relay/heavier wiring, just picked up some of
those 100/80,s at Supercheap and they have fantastic lighting but I am a
bit concerned about burning out the wiring or blowing a fuse.

The neigbour up the road has been running 130/90,s for a year or so
without any ill effects at this stage, but as we are heading away for a
10 day trip back home {South Island} I dont want to get stranded in some
isolated place on the west coast because of a failure.

Thanks

Janet&Jeff.

Reuben Tarran · Post by **Reuben Tarran** » Sat Sep 18, 2004 4:05 pm

As long as you dont change the size of your fuse, you should be ok. One thing
i know as a electrical engineer that most people dont know is that a fuse is
there to protect the circuit, NOT the load on the end of the circuit. This
prevent damage to wiring and switches. Oversizing fuses has obvious
consequences for melting wiring and possible causing a fire, in turn probably
putting your insurance at risk. A 1mm sq wire would probably have a 10a fuse
on it, but someone changing it for say a 25a, you can guess whats going to
happen. 130w in a car is only about 11amps. less when the revs are up as the
alternator is putting out about 13.8v to 14.5v further reducing current. Your
should be ok with upto 130s but dont attach anything else to the circuit, and
if in real doubt check with a auto sparky!

Regards
Reuben

Janet & Jeff Curtin · Post by **Janet & Jeff Curtin** » Sat Sep 18, 2004 4:30 pm

Thanks Reuben,I have removed the driving lights that were running with
the old 60w,s so I suppose thats taken some of the load off,I'll take
afew extra fuses as well and the old bulbs just in case.

Cheers Janet&Jeff.

Reuben Tarran · Post by **Reuben Tarran** » Sat Sep 18, 2004 5:14 pm

They are ok as long as they have their own fused power supply. Generally
anything fitted after factory is supplied from the battery connection with
aftermarket wiring. Nothing wrong with that as long as there is a fuse
nearest the battery. I fitted some day lights to my partners car and it came
as a kit with its own inline fuse and relay, switch, wiring. Works fine.

Regards
Reuben

Janet & Jeff Curtin · Post by **Janet & Jeff Curtin** » Sat Sep 18, 2004 5:32 pm

Ok understand that, it was running of its own rocker switch so probably
was wired to own its fuse.

Thanks

Janet&jeff.

David & Judy Kerr · Post by **David & Judy Kerr** » Sat Sep 18, 2004 5:41 pm

If you are running the higher wattage bulbs you should put in a second relay
to take the load off your light switch I guess. The wiring can take it for
sure but I am not so sure about the switch. On the Yank sites whenever this
subject is brought up it has always been recommended to fit an extra reply.
$50 spent now may save 100's later.

Dave.

Euen · Post by **Euen** » Sun Sep 19, 2004 10:41 am

When you increase the wattage of your lights, you increase the current drawn
through the wiring. Like your lights, the wiring also has a resistance
and the increase in current through the wiring and switch contacts can cause
a proportionate drop in the voltage reaching the lights. This can result in
disappointment as the light output may not really be what you were
expecting.

The increase in current can also put increased stess on connectors,
particularly if they are getting older and have been unplugged a few times.
Make sure they are good and tight.

At a nominal 13 volts, a 55 watt lamp will draw about 4.5 amps, a 100 watt,
about 7.7 amps, a 130 watt will draw 10 amps per lamp. That means on high
beam with 130 watt lamps you will be putting over 20 amps through your light
wiring and existing relay, over double what the standard lights would draw.

The 100s would probably be OK but I would recommend that you have a chat to
an auto electrician who may be able to advise you on whether the existing
wiring will handle the 130s.

Cheers
Euen

Janet & Jeff Curtin · Post by **Janet & Jeff Curtin** » Sun Sep 19, 2004 11:43 am

Thanks Euen I have no intention of going any higher than 100watts, its
just the the old ones were b..y useless out in the country, just to easy
to outdrive.

Cheers

Janet&Jeff

From: "Euen" <euen.burke@xtra.co.nz> Reply-To:
MX5List<mx5list@mx5club.org.nz> To: "MX5List" <mx5list@mx5club.org.nz>
Subject: RE: Headlight Question Date: Sun, 19 Sep 2004 10:41:33 +1200
When you increase the wattage of your lights, you increase the current
drawn through the wiring. Like your lights, the wiring also has a
resistance and the increase in current through the wiring and switch
contacts can cause a proportionate drop in the voltage reaching the
lights. This can result in disappointment as the light output may not
really be what you were expecting. The increase in current can also put
increased stess on connectors, particularly if they are getting older and
have been unplugged a few times. Make sure they are good and tight. At a
nominal 13 volts, a 55 watt lamp will draw about 4.5 amps, a 100 watt,
about 7.7 amps, a 130 watt will draw 10 amps per lamp. That means on high
beam with 130 wat! t lamps you will be putting over 20 amps through your
light wiring and existing relay, over double what the standard lights
would draw. The 100s would probably be OK but I would recommend that you
have a chat to an auto electrician who may be able to advise you on
whether the existing wiring will handle the 130s. Cheers Euen

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