Is this the relay to turn on cooling fan?

I need to troubleshoot my inoperative cooling fan on my 64 S1 coupe. I’d like to send power directly to the fan to test it but not sure where to connect to my 12v test battery. If this is the relay, which wires/connectors lead directly to the motor?g)

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If there is only 1 relay, it is for the horns. Otter switch for the cooling fan is direct wired to the fan. When the switch closes, it completes the cooling fan circuit. Just ground the wires going to the otter switch. With the key on, the fans should come on.

This is the horn relay. On my 62 the cooling fan relay is mounted on the RHS below the header tank.

Fan relay on 62

Disambiguation. For S1, 3.8’s had the relay, 4.2’s didn’t.

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More detailed disambiguation. The deletion of the radiator fan relay took place earlier. Curiously, if the Service Bulletin (D.6) and Spare Parts Bulletin (Q.47) are to be believed, the relay was only removed on LHD cars, commencing at 878021 (OTS) and 886749 (FHC) which translates into a build date around September 1st 1962. The relay continued to be fitted to the RHD cars - until the end of the 3.8s?

@davidxk Makes sense…my '64 LHD coupe (889323) does not have a fan relay (but Im thinking about adding one since Im using a cool cat fan). JS

Jeff that’s a good idea …… I have a modern brushless fan and without a relay when switched off via the ignition switch the slowing fan fed power to the ignition circuit giving a “run on effect” …… took me a while to figure it out that this only occurred when the fan was in use!

Not sure if this helps as have a S3 with air conditioning.
The relay you see is for the horn, as others pointed out already.

For the S3 there are 2 relays related with the radiator fan, the fan is also turning when the AC is on . Both relays are on the top of the radiator


Two relays for S3, on the radiator cowl, either one or two for S2, on the right picture frame. S1’s are different.

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OK thanks! fan tested positive so I guess I need a new ottor switch. Considerong the Aftermarket from SNG at about $54.


I considered and got the CoolCat version to replace the one in my 65 4.2, which had luckily failed in the on position. It has a replaceable switch installed in the brass housing, and uses Lucar connectors.

Not sure if you have a cooling fan relay, but one is highly recommended to reduce the load on the otter switch. In my case, a prudent PO had added a Lucas 6RA relay similar to the one pictured but located on the mudguard above the horn relay rather than at the header tank as on the 3.8s or at the picture frame as on later 4.2s. The mudguard location required a short harness extension to the switch and the fan motor.

+1 for CoolCat’s otter switch.

In my case, the switch is for my Series III but I am sure the quality transcends the various series of E-Types

On a related topic, when adding coolant to the system via the header tank, how much space should be allowed from the coolant surface to the top of the tank to allow for expansion. I’m wondering if it is possible that if there is not enough coolant to reach the otter switch when hot, it will not turn on the fan. Is this possible?

I like to just keep the internal pipe that traverses the header tank covered with coolant.

The 3.8s have the otter switch mounted on the top of tank, and covering the internal pipe leaves enough room for expansion of the coolant, which will then reach the switch bulb when hot. Although the same C18559 switch was used on both Series, it was moved to the lower front of the tank on the 4.2s, possibly to reduce the chance that low coolant level would result in failure of the fan to proceed.

For greater certainty, a slight overfilling of the tank and running the engine up to temperature will result in the cooling system finding its own level. Use a container to catch the overflow from the drain tube…

+2 for it!

The switch was moved to the front of the tank because the 4.2 tank has a convoluted internal baffle system. A pipe runs through the header tank which directly connects the thermostat output to the left corner of the radiator. The pipe lies along the front side of the tank, and the otter switch passes through both the tank and the internal pipe. This allows the otter to sense flowing coolant, rather than the cooler, stagnant fluid in the tank. There are some slots or discontinuities in the pipe which allow air to bleed out of the pipe and out through the tank. But otherwise, fluid doesn’t readily communicate between the internal pipe and the header tank. For the most part, the otter switch will be in contact with flowing coolant as long as there’s enough juice to be pumped around the engine. Long winded explanation, but that’s why the fan switch moved. The fluid level is somewhat less critical in the 4.2 than the 3.8. This may not be the case with aftermarket heater tanks, which are a bit of a crapshoot.

Regardless of which tank you have, the best thing to do is to overfill it. The first time the engine runs, it will piss out any excess coolant. After that, the level will be correct. Messy, but certain.

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Wow…im always amazed at the information I can get on this forum. Thanks all

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