In a message dated 11/10/2000 6:31:53 PM Eastern Standard Time, Dave
Stauffacher wrote:
> Somewhere in the fog banks of my memory, I recall a discussion on the list
> about be advantages of installing a relay into the headlight circuit. I
> remember the main point being that the current load is not running through
> the switch but through the relay. That sounds like a better design than
> that current situation where the light switch takes the full current load.
>
> My question is this: is this really a concern?
>
Dave,
I found this post in my out box, gathering mildew. I thought I had sent it,
but I hadn't. Hope it's not to late to be of some help. Just my two-cents
worth.
Adding a headlight relay may or may not be worthwhile. If your wiring is in
good condition, and you are not using much more than stock wattage
headlights, a relay won't help much, not enough to really be noticed. If your
wiring is bad, a relay *may* help. If you are using very high powered
headlights, a relay is recommended (even mandatory), but the relay itself is
not enough - wiring upgrades are also needed.
Connectors, switches, and wire all have resistance. Resistance drops the
voltage available to the headlights. The more resistance in the circuit, or
the more current the lights draw, the more voltage dropped. (You have a copy
of my book, so you might want to read chapter 3 for more details on this).
Power to the headlights in your '70 TR6 (and typical of the TR250 through the
1972 TR6) is as follows:
>From the alternator to a spade connector on the ammeter,
>From the ammeter to a terminal on the ignition switch,
>From the ignition switch terminal to a bullet connector,
>From the bullet connector to the headlight switch,
>From the headlight switch to a bullet connector,
>From the bullet connector to the dimmer switch,
>From the dimmer switch to a bullet connector,
>From the bullet connector to the headlamp socket on the LH side of the car,
and,
To another bullet connector and socket for the RH side.
The last three items are duplicated for the high and the low beams.
After you install the relay, my recommend wiring would be:
>From the alternator to a spade connector on the ammeter,
Through the ammeter to the battery terminal on the starter solenoid,
>From the starter solenoid to the connector block on the inside left fender,
>From the connector block to the relay,
>From the relay to a bullet connector,
>From the bullet connector to the headlamp socket on the LH side of the car,
and,
To another bullet connector and socket for the RH side.
As you can see, you have only eliminated two connections, but you have
bypassed the headlight and dimmer switch contacts. You could eliminate two
more connectors if you skip the connector block and wire the relay directly
to the solenoid connection, but this will require routing wire from the
solenoid, through the firewall, behind the dash, to the relay, and then to
the bullet connector. You will have also replaced about 25% of the original
wiring, but you will still have the long run of original wiring from the
relay to the headlights.
You could splice a wire into the main alternator wire, and connect the relay
here, but that adds a connection where you can afford added resistance least
of all, as the main alternator lead carries a lot of current.
If you use fuses (which I don't recommend) or a circuit breaker, you will add
two more connections (maybe four, depending on what type of fuse holder you
use).
Probably 98% of the folks on this list are using their cars the way they came
from the factory, without relays, and without problems. Personally, I would
be more inclined to get my wiring in good condition rather than adding
relays. After-market relays are usualy rated for 30 amps, and cost around
$5.00. The TR/Lucas headlight switch costs around $40.00 or so, and is
probably rated a bit less than the relays, but I don't know the actual
rating. Experience has, I believe, shown it to be adequate for stock lighting
(European spec TR6s came with 60/45 watt headlights). Corrosion, dirt, and
plain old wear account for most failures. If a relay goes bad, it is easy to
pull it out and pop in a new one, but it is a bit harder to replace the
headlight switch.
If you have, or want to add, high powered lights, I would wire it as above,
except run all new, large gauge, wiring to the relay, and from the relay to
the headlights, using as few connectors as possible.
Dan Masters
Alcoa, Tennessee
Triumph TR 250 - TR6 Electrical Maintenance Handbook:
http://members.aol.com/danmas6/
Stuffing a V8 into a small British sports car:
http://members.aol.com/danmas/
MGBV8 Newsletter:
http://members.aol.com/danmas4/mgv8.htm
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