Lotus Elan

Plus2 Electric windows solution

PostPost by: TonyA » Wed Jan 03, 2024 3:39 pm

Happy NewYear to all. I

had been struggling with very slow windows and had searched the forum for the solution. The solution is in three parts: First: heavier gauge wires and earths to the motors, second: use of relays to shorten the lengths of the heavy gauge wires and reduce the load on the ancient original wiring and switches. Third: use thin wall modern wire, which has amp rating to overall diameter of twice the traditional stuff; among other things it allows to go into the door wiring tubes .

Biggest problem was finding the right circuit design. It is important to note that the Plus 2 window motor and switch wiring differ fundamentally from its baby brother, The baby elan has a classical arrangement: two terminals in the motor : the switches reverses earth and live for up and down: it's the configuration you find on Google and Youtube. BUT, not so with the Plus2 which has in effect an UP live, a DOWN live and an earth. The most commonly shared window relay circuit on the forum involves four 5 contact relays and it's not obvious that this is for the baby elan arrangement and most definitely NOT for the Plus2 .

On mine and some other variants of the Plus2, there is an additional feature: the power for DOWN comes from a permanent live ( on 3 Fuse for 3 fuse box cars) and the UP live from ignition switched ( fuse 5 on 3 fuse box cars) Apparently this was a safety feature in case you left a kid in the car without the ignition keys !

I decided to simplify by having both UP and DOWN switch feeds to the relays from the permanent live. This also simplifies the switch wiring because you only use one column of three contacts on each switch. The original functionality requires wiring all six switch contacts, which in the tight space, is error prone and very fiddly.

I have attached two diagrams: one for the simple UP and DOWN from the Permanent Live, and another circuit for those who wish to retain Permanent Live for DOWN and Ignition Switch Live For UP. The rating for fuse 1 was 50Amps originally when it carried the full motor current; now it carries only the relay switching current so can be MUCH lower and safer for the original wiring loom.

I used 29Amp thin walled wires: about 2mm sq. . Four contact " Normally Open" relays are reqd : 4 in total : uU and Down, each side. I used blade fused relays for safety and found 15A on each OK. For wiring the relays, I used relay connector blocks which usefully slide clip together to make a pair : this makes unplugging to change the relays in the future much easier. Each relay connector block usefully has a mounting hole and when clipped and paired, and each relay pair can be attached to the wiring harnesses at the left and right ends under the dashboard with 2 zip ties. Access for replacing relay fuses or indeed changing relays, relatively easy. I took the motor lives directly off the solenoid ; one for left and one for right, each then split into up and down. 2 small holes with grommets carry the live wires thru the firewall into the dash underside on left and right. Motor earths I connected to the chassis mounting bolts on each side of the transmission tunnel near the dashboard bottom.

All this done needing only to remove the two dashboard under panels, the ashtray and door panels but leaving the dashboard in place. Windows now zoom up and down like a proper car..!

IMG_0639.jpeg and
Plus2 Window relay scheme: Up and Down from perm live :
IMG_0640.jpeg and
Plus2 Window relay scheme: UP sw ign Down perm live
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PostPost by: Johnny America » Wed Jan 03, 2024 11:07 pm

Tony, thank you very helpful and care write up. Looks like a future modification I will employ.
1969 Lotus Elan +2 4 speed - Barn find and currently undergoing recommissioning.
1979 Lancia V6 Group B Rally Car
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PostPost by: Stagmatt » Thu Jan 04, 2024 7:14 pm

this looks like a clever improvement! Thanks a lot for this writeup, very helpful when it is time to put the loom right.

Wishing you a Happy New Year,
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PostPost by: stugilmour » Thu Jan 04, 2024 9:21 pm

Nice write up Tony. I had never thought of the ignition triggered up wiring as a safety feature, but it makes sense. I wired both up and down to purple - hot at all times - fused which I find handy.

I fiddled around with the fuse size and also found 15 amp the sweet spot. 10 amp would sometimes blow at stall when seating the glass to the gaskets.

Another top tip, particularly for folks in North America. The Plus 2 motors are readily available here thru your local parts store. They are Delco units used in many seventies GM sedans. I have posted the call up before. Cardone supply a completely rebuilt motor if you provide a core. Make sure you retain your drive gear.


In a very interesting Lotus quirk, the motors are switched side to side from their location in a GM car; ie if you want the left side Plus 2 motor order the right front motor for a ‘69 Chevelle or similar and you will be good to go.

HTH. I see a few folks are probably at this stage on their Plus 2 projects. I found the new motors combined with similar wiring upgrades as outlined by Tony have worked out well.
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PostPost by: HCA » Fri Jan 05, 2024 9:38 am

If you are re-using the original switches with clean contacts and all the new wiring you have installed, I doubt very much that the relays are adding any benefit. Relays are only necessary where the switch contacts or switch wiring cannot take a high load. I had mine wired generally as you have - quality wiring, clean earth and contacts and no relays. Works a treat...
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PostPost by: gus » Fri Jan 05, 2024 4:56 pm

I agree with Hal on this, the bigger wiring is 99 percent of the job.
When I bought my car it was merely 14 years old and the windows would not go up by themselves with the car off. One had to help them or fire the car up and rev the generator up.
I replaced the grounds and all wires from the fusebox to the doors[later inside the doors] with 14AWG wire.
Both windows will sail up and down at the same time with the car off and it has been the better part of 20 years since that work was done.
Still factory switches.
Not posting just to be critical, it is just I fear the added complexity, each connection being a potential failure point.
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