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6 cyl Bristol cars Type 400 to Type 406

Circuit Diagram for LIR Tpye L1 Relay in 401/403

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Old 24-04-20, 11:40 AM
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Default Circuit Diagram for LIR Tpye L1 Relay in 401/403

The 401/403 has a lockout in the electrical system so the High Beam and Fog Lights cannot be on together I believe. This is done using the LUCAS LIR Type L1 Relay mounted up behind the dash. It takes input from the Fog Light Switch and sends it off to actuate the Fog Lights. There is also input from the high Beam Warning Light which serves to cancel the Fog Lights when High Beam is selected. At least that is what I work out from various circuit diagrams. The Relay also has an Earth input. I am doing a rewire using a Vintage Wiring Harness Loom. I cannot figure out the actual layout of the 4 wires to the 4 screw in tabs on the Relay. I can get the switch to throw but not turn the lights on. Any Ideas of what goes to what.
Greg Mead 403 Sydney Australia
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Old 07-05-20, 09:38 PM
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Default Fog Lamp Circuit

Quote:
Originally Posted by Greg Mead View Post
The 401/403 has a lockout in the electrical system so the High Beam and Fog Lights cannot be on together I believe. This is done using the LUCAS LIR Type L1 Relay mounted up behind the dash. It takes input from the Fog Light Switch and sends it off to actuate the Fog Lights. There is also input from the high Beam Warning Light which serves to cancel the Fog Lights when High Beam is selected. At least that is what I work out from various circuit diagrams. The Relay also has an Earth input. I am doing a rewire using a Vintage Wiring Harness Loom. I cannot figure out the actual layout of the 4 wires to the 4 screw in tabs on the Relay. I can get the switch to throw but not turn the lights on. Any Ideas of what goes to what.
Greg Mead 403 Sydney Australia
Greg,

My 403 is stripped down and nearly ready for its new wiring loom. So seeing your question I spent this afternoon looking at the Fog Light circuit for you. I attach some jottings and a marked up circuit diagram. Here is a description of how the circuit works to go with it.

There are actually 5 connections on the relay, but only 4 are used. W1 and W2 are the two ends of the relay coil. The single make/break normally closed contact is wired between terminals C2 and C3 - C1 is not used. The relay contact is made when the coil is de-energised, and breaks when it is energised. The feed for the coil is taken from the Main Beam output terminal of the dip switch.

Both fog lamp filaments are fed from terminal C2 on the relay. They get their power via the relay contact. The relay contact gets its feed via terminal C3 which is fed from the Fog Lamp switch. The Fog lamp switch is in turn fed from the sidelight output contact on the main lighting switch.

So, assuming at least the sidelights are on, pulling the Fog Lamp switch will turn on the fog lamps. If the headlamps are turned on as well, the fog lamps will go off if Main Beam is selected, or stay on if Dip Beam is selected.

Wiring-wise - looking at the circuit diagram - the top terminal on the relay is W2, then W1, then C3, C2, C1 as you go down.

In the center of the wiring diagram, starting at the top, you will see four terminal blocks. I have labelled them A,B,C,D working down. On the car, they go A, B, C, D from right to left across the dashboard.

On my 403, there is a light green wire on W2, which goes to the bottom terminal of block C.

A dark green wire on W1 goes to the bottom terminal on block D.

A Violet wire on C3 goes to the bottom-but-one terminal on block D.

Two thicker wires of an indeterminate brown colour (crimped together) go onto C2 - these disappear into a thick multicore part of the loom very close to the relay (these are the ones that go out to the Fog Lamp filaments).

C1 is not used.

Hope that I've got that all correct. It's not easy to trace on the circuit diagram.

Incidentally, the contact on my relay was quite corroded. I dressed it with a contact file and it now tests out OK.

Best of luck and let us know how you get on.

Rgds

Mike Brooks
403-1402

Last edited by mikebro; 07-05-20 at 10:02 PM.
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Old 08-05-20, 07:37 AM
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Something else to be aware of, when dealing with cars of that and indeed later eras, that use screw up electrical connectors, is that copper is a soft and ductile metal that slowly, over time, simply moves out of the way if put under pressure. A bit like me.

Which is of course exactly how a screw up terminal works, but only for a while.

I see a number of these screw type terminals in the circuit diagram, so it might well be worth quickly going around all these and making sure that they are all still tight. You might be quite surprised.

(The same issue can also arise in your house wiring, which would take rather longer to check over)

Roger
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