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One for the auto-electricians

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After too many gremlins (such as losing all headlights one night 200 kilometres from home) and some burnt out switches and indicator stalk (gotta love that burning wire smell), I'm doing a major re-wiring of the S2, and I'm just wondering.... how many amps do the rear indicator lights use?

My new wiring loom is nowhere near ready to connect to the battery, so I can't turn them on and check myself. I've done plenty of other electrical work, but this is the first major automotive wiring I've done. 12volts is an art in itself.

The reason I'm asking is that there are options regarding the type of wire to use. I only want to use the thinnest wire that will still get the power through at the required efficiency.

So your help will be appreciated.

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Power (Watts) = V (Volts) x I (Amps)

Therefore, I = P/V

I = 24*/12 * is the watt rating of your indicator bulb (you need to check what is printed on the bulb)

= 2 Amps. If you have two bulbs on one circuit, then 4 amps etc.



Edited by iainskea
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Indicator lamps 21W each, plus one 5w repeater on the side, and a 5W in the dash, so 52W, at 12V that's just under 4.5 amps, but I certainly wouldn't run wire that thin. You need the wire to be protected by the fuse, and the indicators might be on the same circuit as other components so you can't change the rating of the fuse (if that's the case).

I'd go for at least 8 amps, but probably 10-15 amp wire(for each side, but double that for anything taking power tot he switch due to hazards putting both sides on at the same time), the wire will heat slightly due to its internal resistance, taking more of the power from the lamps, causing more heat etc. The larger it is, the over the resistance over a given length, the less heat generated in the wire.


Just checked fuse, it's a 10amp, so wire no less than 15 amp at any point.

Edited by andydclements
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Thanks for the quick responses.

I've used calculators on sites such as etc, and they backup what you've said. I just wanted to send the question out, because I noticed that Lotus (as well as almost every other car maker) seemed to use the same gauge wire between + and a single globe as they would use to power several globes & accessories. These wires are capable of carrying up to 20-30A.

I thank you for your replies. I will continue using wire greater than what is required, but not necessarily as overboard as the OEM.

Andy, you mentioned yours was a 10A fuse. Every one of my fuses is 30A, which matches the Lotus original workshop manual I got with the car. Interesting?

By the way Hilly, nice beast. I've been watching your conversion. Wish I could do the same here, but Australia has very strict guidelines on modifications (in particular engine size versus car weight). I bought a 3.8 litre V6 to put into mine but the capacity is too large for the weight of the car. Apparently here in New South Wales, for a normally aspirated engine, you can only put an engine of a capacity that is 3 times the weight of the car, so I would be restricted to something a little over 3 litres. That leaves something like a 2 litre Japanese turbo as an option to get some performance.

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TBH I didn't look at the model you have, I looked at the fuse for an S3, which is 10Amp in the Manual, but think of this, if your fuse is 30amps, what will give out first should a short occur somewhere in the indicator system, the wire you plan to use or the fuse. If it's the fuse that's OK, if the wire would give out first, that could lead to a fire.


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I agree totally. This is probably why my headlights failed, and my indicator stalk burnt out etc. The manual says all 12 fuses are 30A. I've never seen this in any other vehicle (all fuses for every system the same).

I plan to install low amp fuses in my new harness until I find the rating that doesn't blow. eg. if I put in a 10A and it blows, then I'll put in a 15A, and if that blows, I'll put in a 20A etc until I find the lowest amperage fuse that won't blow when the system runs correctly. I'll check this against what is actually running through the wire (as per calculators and previous posts) to determine if everything matches the expected ratings.

With the planned wiring diagram, I expect a lot of 10A fuses (compared to the 30A originally).

If all goes well, no gremlins, bright lights, no burning wires, and happy driving.

Edited by USAndretti42
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Most of the fuses in the federal S1 are 17 amps, IIRC. I understand, though, that a UK/RoW S2 will be much different.

If it doesn't already, the turn indicater/headlight stalk should be wired to relays, and the relays should do the lighting of the lights. Early federal S2s still don't do this, and 20min. with the high beams on can melt the stalk, even with the stock low-wattage lamps.

- T

Tony K. :)


Esprit S1s #355H & 454H

Esprit S2.2  #324J

1991 Esprit SE

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  • 1 month later...

My 81 S3 has the Stalk directly wired to the outside pair of lights and the inner pair of lights are routed through a high beam relay and a low beam relay. I too had a load of smoke coming out of the stalk one evening, it had melted the contacts inside. I havent had the problem again since replacing the stalk.

Typical Lucas wiring - poorly thought out. All the switches in mine are open at the back letting all the dirt in until one dark night out go the lights. Bullet connectors full of corrosion. Multiple earth paths, mostly corroded. Ive had no end of trouble with the electrics, theres always something different that stops working. It keeps you guessing!


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