Series 1 main wiring

Does anyone know where the two heavy wires coming off the main harness just below the brake pressure switch go to? They are a round push connector…

Welcome to the forum.
You probably need to specify which year your car was built. The brake pressure switch moved from the picture frame to the firewall with the later cars.

This is a Series 1, 1966 FHC 4.2

I can’t figure out how to use this forum…I can’t find my original message so I don’t know what I did not say. How does this thing work?


Your posts look fine from my end.

so do you have an answer?

Hi hope you’ve resolved this…
But if not what colours are they … that will give us a clue

Heavy wires in that area might be for the horns. They’re mounted on the bottom of the picture frame.

I just took a look at my1967 S1 2+2. The harness leading to the brake pressure switch, mounted down low on the drivers side footwell panel, is a solo harness about 12" long leading back to the main harness. No branches or heavy wires.

To me, a heavy wire is 12 or 14 gauge. Quite a distance from the pressure switch but in the same side of the engine compartment, there is a horn relay mounted on the back side of the fender well, above the front of the battery, that uses heavy wires. And of course there is heavy wiring at the altenator and voltage regulator.

As noted by Danny, if you have the wire colors and rough estimate of the gauge, a review of the wiring diagram for components in that area should get you an answer.

Not sure as we need additional information. It depends on the gauge of the wire and exterior color of the insulation. Attached is a chart of Lucas wire colors that helps in identifying the purpose.


The horns are in the hood

A point to consider - the horns on the 4.2 were moved from inside the bonnet, like the 3.8’s, to the picture frame. Your wiring loom may be for a later year 4.2.

That chart is worth snipping and saving. Thanks for posting it.

On a similar note, the brake light switch moved from the picture frame to the firewall during the 1966 model year, so referring to the “two heavy wires coming off the main harness just below the brake pressure switch” is ambiguous for a MY 1966 car. Please tell us where your brake pressure switch is so we have a better idea where your two heavy wires are. As already mentioned, the colour of the wires and their gauge would also help. Even better, include a photo. Lots of folks here willing to help, but @drobert5 could make it much easier for us…

that would mean mine is an early 4.2 if it is like the 3.8’s

I have an early 4.2 with the horns in hood…In that case Dan… the horn wires will go into the hood with the rest of the lighting wires etc. so won’t be horns ( purple/yellow)

Probably the wires are for the cooling fan relay green plus black maybe
Green feeds into relay a separate wire black/red from otter switch in header tank and black/green to the fan ( both the otter switch and fan are earthed to the car via black .
Hope this helps

My car, built 9-65, has the brake switch on top of the picture frame and the horns mounted under. Without the OP clarifying what the setup is on his car, it’s all speculation as to what the wires are for.

Daniel, welcome to the forum, and you’ll find some there are people here with amazing expertise on these cars and will bend over backwards to help. But it would also be helpful if you were more forthcoming with information that will help people understand the situation better and thus be able to provide the best advice. Several people have asked for key pieces of information, and without that there’s a lot of guessing. Is your car one with the brake pressure switch mounted forward on the picture frame, or back on the firewall? What are the colors of the wires in question?

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Mine is #30598 and the horns are in the bonnet for sure. I also have a section of wire that is a separate pair with round ends one end and clips on the other that I do not know where they go either…

So it appears to be a 1965 LHD FHC … but you still need to tell us the colours of the wires in addition the horns should have been on the picture frame not in the hood … maybe a replacement bonnet.
Unless you give us the colours of the wires and or photos we can’t really help you
Best wishes