Lotus Elan

Ignition Switch Rating

PostPost by: oldelanman » Fri May 17, 2019 2:54 pm

I need to replace my ignition switch and according to Robinshaw and Ross the original fitment on the S4 was a Lucas 47SA 34680. However, the attached info on the switch indicates that the IGN (Run) contact is only rated at 5 amps which doesn't seem high enough when the main fuse is fed through it as well as the coil, which probably draws 5 amps on it's own. Maybe that's why it's only lasted 50 years :roll:
Any thoughts?
lucas-ignition-switch-34680a.jpg and
Roger
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PostPost by: ericbushby » Fri May 17, 2019 5:30 pm

Hi Roger
It seems to me that when the switch is in the run position (AUX/IGN ) the auxiliary circuits are supplied with a 15 amp contact, leaving the ignition supplied by a 5 amp contact. This would satisfy your requirements.
However I do not have a circuit diagram to check this so I could be wrong.
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PostPost by: oldelanman » Fri May 17, 2019 7:29 pm

ericbushby wrote:It seems to me that when the switch is in the run position (AUX/IGN ) the auxiliary circuits are supplied with a 15 amp contact, leaving the ignition supplied by a 5 amp contact. This would satisfy your requirements.
However I do not have a circuit diagram to check this so I could be wrong.

Hi Eric,
I see your reasoning but in the S4 contact #4 (AUX) just feeds the cigar lighter, radio and horns, all the other switched circuits including the ignition circuit are connected to contact #2 (IGN) so the load through that must exceed 5 amps when wipers, heater blower, brake lights and indicators for example are all on at the same time. Maybe I'm missing something obvious or perhaps I'm misinterpreting the switch diagram..I did find another one on the Holden site which is different.
I'm probably over-thinking this !
63480-switch.jpeg and

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Roger
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PostPost by: Chrispy » Fri May 17, 2019 11:31 pm

I just did a complete re-wire on my Plus2 and this was on my mind too.

I ended up wiring in relays for the blower, headlights, fan, horn, and wipers. So the only thing that is going through the key switch is the coil, gauges, parking/brake lights and windows.
Chris
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PostPost by: ericbushby » Sat May 18, 2019 9:11 am

Roger, yes I see what you mean.
On my S3 the side lights, headlights and horn do not go through the switch. That would be useful for parking lights for instance and I think that is probably correct.
It depends what they call auxiliaries.
My car was rewired before my time when it was converted to negative earth and there are some differences to the wiring diagram.
Thankyou for bringing this up. It is something else that I have not noticed before. We learn all the time don`t we.
Your second switch diagram says the rating is 16 Amps. That may be the total current not per contact.
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Eric in Burnley
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PostPost by: Craven » Sat May 18, 2019 10:36 am

There is a different rating for switching current and current carrying capability, it seems unlikely that you switch on with heater, indicators etc all drawing current at the same time as they all have their own switches.
Maybe.
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PostPost by: oldelanman » Sun May 26, 2019 3:39 pm

Well to put my mind at ease on this I took my old switch apart ....

All the contacts inside are the same size and I can't see any reason why the IGN contact would be rated lower than the others at only 5 amps. There was no sign of arcing or burning but there was a fair amount of corrosion particularly on the IGN contact .... the likely reason for the significant voltage drop I was experiencing in that circuit. I had tried dousing the switch with contact cleaner but it made no difference, the new switch has resolved the problem.
img_20190526_120507.jpg and
img_20190526_120616.jpg and
BTW For anyone contemplating a switch change I can confirm that it's possible to remove it by just pulling the dash forward an inch or so - no need to disconnect any cables or wiring. Just check everything works when you push it back before you refit the bolts !
Roger
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