Circuits needing relays

[fattogatto]

I am completely re-wiring a 1967 UK version S3 Elan. I have the option of using up to 11 relays with my current (no pun intended) equipment. Choices are:

Headlights - main
Headlights - dipped
Left window up
Left window down
Right window up
Right window down
Horn
Electric radiator fan
Heater fan

Any other suggestions?

Thanks,

[john.p.clegg]

One for the accessories and one for the ignition to relieve the stress on the ignition switch ?

John

[Andy8421]

Wiper motor draws significant current, particularly with a dry screen. Two speed motor / self parking will need some thought though to use relays.

The solenoid used for pre engaged / geared starters can draw significant current if you have one fitted.

[mbell]

One for the accessories and one for the ignition to relieve the stress on the ignition switch ?

John

I've been starting to think about custom loom for my plus 2. I agree with John on this, I was planning a couple of big relays for switching the ignition circuits on.

Basically any device that pulls a significant current would go through a relay.

My first step with be to spread sheet every electrical device in the car to map out wire colors, location, current, power source. From that I can identify relay and fuse requirements.

[fattogatto]

Thanks for the replies.

The draw from an ignition circuit, especially an electronic (e.g. Pertonix) should not be much. Although, with an extra relay available it would not be a bad idea.

Same for a gear-reduction starter. The wire from the start switch merely triggers the solenoid, acting as a type of relay itself. At least that's always been my understanding. Someone please correct me if I am wrong.

[mikealdren]

A rather simplistic approach but if it has a thick wire, consider a relay!

Mike

[mbell]

A relay for ignition circuit is good idea to separate the pertronix power line from the coil supply for the tach. I also run elec fuel pump, rev limiter, alternator line of that circuit via the relay. None of it is that high power but relay is good for extra reasons:
- relay is triggered via a fuel cut of switch so crash will kill fuel supply and engine
- removal of the relay gives good security measure
- the relay will trigger with a voltage lower than 12v, so even if isn't switch isn't great you get more reliable operation
- relay is less likely to get a bad connection and much easier to fix/replace

I am not sure what the current pull for the solenoid is but I'd expect it to be quite noticeable, amp or so, as quite a heavy device. So worth considering a relay but given amount of time it is active it might just be a little bit of over kill but a lot of the above probably applies...

[fattogatto]

Gear reduction starter research shows use of a 12 - 14 gauge wire recommended for the starter switch with typical amp draw maxing out around 15 (which is max for a 14 gauge wire at normal temps), depending on length of wire. Not a bad idea to use a relay for the starter and 12 gauge wire from the relay..

Thanks,

[gus]

relays are to protect cheap switches[in new cars] or enable automation

they add failure points and will become impossible to decipher years from now

How many switches have you replaced?

I have replaced my microswitches, kill switch....that's it

replaced horn and low beam relays

IF you have 2 fuse wiring, it could use more fuses, the last +2 had 4 which I think is fine.

Increasing wire size and ground size is really all that is needed.

adding complexity is asking for trouble.

[StressCraxx]

I am completely re-wiring a 1967 UK version S3 Elan. I have the option of using up to 11 relays with my current (no pun intended) equipment. Choices are:

Headlights - main
Headlights - dipped
Left window up
Left window down
Right window up
Right window down
Horn
Electric radiator fan
Heater fan

Any other suggestions?

Thanks,

Charlie,
If you Elan is a Coupe, another circuit that would benefit from a relay would be the rear window defogger.

Regards,
Dan

[Galwaylotus]

Thanks for the replies.

The draw from an ignition circuit, especially an electronic (e.g. Pertonix) should not be much. Although, with an extra relay available it would not be a bad idea.

Same for a gear-reduction starter. The wire from the start switch merely triggers the solenoid, acting as a type of relay itself. At least that's always been my understanding. Someone please correct me if I am wrong.

The solenoid on my high-torque starter pulls 35A. According to the Bosch Automotive Handbook, this type of starter/solenoid will pull over 30A so a relay seems a good idea.

[billwill]

The solenoid on my high-torque starter pulls 35A. According to the Bosch Automotive Handbook, this type of starter/solenoid will pull over 30A so a relay seems a good idea.

Aye, but you need a high-current contacts relay for that. Which is exactly what the old starter solenoid is. It's only a relay in any case.

[Galwaylotus]

I know that but I didn't have one and I did have a 40A continuous relay so I've used that instead.