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JohnnyMead
01-24-2010, 09:02 PM
I'm thinking about using relays in the headlight circuit of my still positive ground TR3. Can I use the common cube-style automotive relays? It seems like the relay coil could be wired either way.
Thanks,
John

TR3driver
01-24-2010, 09:26 PM
For the most part, yes. The common relays don't care about polarity, however some of the sockets sold with them have suppression diodes wired into the socket. They will also work fine, as long as you observe the polarity of the diode.

JohnnyMead
01-25-2010, 09:33 AM
Thanks Randall. What I'm thinking about is a relay to substitute for the dimmer switch. With my long legs and clumsy feet I don't have much foot room between the dimmer bracket and the clutch. A relay and a little switch under the dash would eliminate the bracket.
Anyway, its winter here and I'm dreaming up silly little projects!
John

TR3driver
01-25-2010, 10:05 AM
A relay and a little switch under the dash would eliminate the bracket. If you are going to go that far, why not use two relays? That way the headlight current doesn't go through the original panel switch either, which extends the life of the switch and gets just a bit more power to the bulbs for brighter lights.

I'm actually going rather overboard and using 4 relays on my TR3, one for each filament, so I can have separate fuses for each side. I had only two relays on the TR3A, with a fuse for each one; but having one of the fuses fail while descending a mountain at 80+ mph on a dark night convinced me that I would really rather have separate fuses for each side.

JohnnyMead
01-25-2010, 10:34 AM
Yes, in fact I was thinking about a relay for the light circuit. I like your multiple relay design. Where did you mount them?

TR3driver
01-25-2010, 11:03 AM
For the current project, I am mounting them on the back of the headlight buckets, where they will be mostly out of sight and yet easily accessible (by pulling the bucket). The main harness will remain intact and original, with the only visible mods being a new Lucas fuse block near the original one, and two wires from the new fuse block to the relays. My theory is that the headlight pigtails will also look fairly stock, except for the extra wire.

But I haven't gotten very far with it; got distracted when I realized that the original brake light switch only comes on when I'm about to lock up the brakes. In between rain drops, I've added a bracket to mount a mechanical switch so it rides on the pedal. Here again I wanted to hide it, so it's under the dash this time (TR3A had it mounted on the pedal box under the hood, where there is a very convenient original hole).

PS, I also discovered that my right headlight is losing over 1/2 volt inside the original headlight connector. Both sides will be getting new connectors along with the relays.

JohnnyMead
01-25-2010, 02:04 PM
Yeah, I've seen posts about the stock brake light switch. All my old cars (jeeps, VWs, and so forth) have had the brake fluid activated switches, but my every day modern cars all seem to have pedal micro switches.
Thanks again for the relay ideas.
John