Morris Minor Owners Club

My 1967 Morris has an electrical fault stopping the horn and heater fan working, all the other electrical components are working.

I have checked the horn and it works off the car, but I do have doubts about the heater motor, could a fault here stop the horn working?
The car had a full upgrade including a new 2 speed heater fitted a few years ago (2016) by Charles Ware and was working fine.

Any advise of how to check if its the heater or any other fault would be much appreciated.

Chris Saunders

It’s an odd fault because the heater and the horn are not on the same circuit. The horn is permanently live (purple) and the heater is only live when the ignition is on (green). I don’t have access to a wiring diagram right now. I’d suggest checking the connections at the fuse box. Check the connections are clean and tight. Disconnect battery before fiddling

Do you have a multimeter so that you can measure voltage and resistance? This will aid in fault finding.

Unless the wiring has been "modified" then the faults will not be related. As above, check all connections around the fuses - even unfused circuits use the fuse box as a junction/distribution area. Once that's done, ackle the two faults separately.

Let's start with the horn that should not require the ignition to be on. Remove the purple wire from the horn and check whether 12 volts are present (observe the polarity of the car). If "no" then the problem is with the supply. If "yes". then reconnect that wire and remove the purple and black wire. Get a piece of new wire, connect one end to the now empty terminal on the horn and touch the other to earth. The horn should sound.

Now use the meter to test continuity from the purple/black wire to earth. There should be none (infinite resistance). Press the horn push and the resistance should drop to zero.

Report findings for further advice.

Pleased to report after following your advice I have traced the fault in the horn and it is working again.

Regarding the heater fault, any advice on how I can check the heater fan ?

Thanks for your help, best regards Chris.

Excellent news on the horn, well done.

The heater is a simple motor, and rarely fails. It needs a good earth and a supply via the switch. The switch is off, on via a resistor, or on direct.

If the switch is clicking normally and not feeling loose and wobbly, then I suspect the supply. The only difficulty is knowing how CW wired it up when they fitted it. Somewhat bizarrely, the standard heater takes it's supply from the back of the instrument voltage stabiliser on the rear of the speedometer. The question is, did CW do the same, or run a separate supply from the fusebox?

First, check the heater and see what colour wires are going in to it. Hopefully there will be a black one - is it connected to a good earth? If no, then connect it and check for correct operation. The other wire "should" be green or perhaps green and yellow. Trace where it goes. You may have to remove the speedometer. If so, disconnect the battery first as it is easy to short wires to earth as you pull the speedo out.

With the speedo safely out and supported, you can reconnect the battery (with your long arms and third hand ) and, using the multimeter, check for 12 volts at the point where the heater wire gets its supply.

On the back of the voltage stabiliser, there should be a single terminal and wire going to the fuel gauge and a double terminal, one wire coming from the fusebox and the one going to the heater (if that's how it was wired).

The wires from the heater may go to bullet connectors before going anywhere else. If so, it is easy to connect a supply and earth direct from the battery, just to confirm that the switch and motor work OK. It is possible that the supply wire has become disconnected from the switch, but that is unlikely. You would have to remove the heater and open the case to check and rectify.

Thanks for the guidance I will try and check it out over the next couple of days and let you know how I get on.
All the best, CHRIS

Here are some pictures of the original wiring from my 1969 car.

Picture 1 shows the wiring to the heater toggle switch from the inside of the heater. The wires are: 1) green 2) yellow with a green trace. The wires should have a knot behind the grommet on the inside of the heater (picture 2) to prevent them being pulled off the switch connectors.

Picture 3 shows the yellow with green trace wire from the switch going to the heater motor. The green wire from the switch goes as Simon says above. The black wire from the motor is the earth.

Stephen

In your introduction you say you have a 2 speed heater fan?

If so it will not be like the above you will either have a resistor or 2 connections to different points in the windings on the motor and a switch with 3 wires coming out of it, one input and 2 out which can either be switched to position 1 or 2 or 1 goes live on position one and both on position 2, the other side of the motor will be earthed as above.

If you can get some pictures of the motor and switch wiring and see if there is a resistor we might be able to help more.

Pleased to say I have found the fault, a bad connection from behind the speedometer.
I can't thank you enough for your help and guidance.

Until the next time my Morris needs attention.
All the best, Chris

Well done. A nice, easy fix - we like them! My SII heater stopped working too recently- and I found I must have pulled apart a connection while I was faffing about in the parcel tray the previous day..........