Rover passed MOT. Emergency fix of the horn.

Barten

Barten

Active Member
Today my Rover 3500 from 1971 passed its MOT today, yess!
The horn did not work. I have tried to clean the contact on the stalkswitch and I have checked that the horn works if i feed it directly from a battery. The problems seems to be low voltage on the current supply when the horn is activated. I measure 8,5 V when the horn is activated and that is obviously not enough.
Time was short and to overcome the problem I used a redundant foglight switch for the horn and took current directly from a redundant switch on the fuse box. With around 12 V on the horn it worked ok. only one that is. With the switch marked it was Ok for the tester.
Now if someone has a good idea where the hidden voltage can be I would love to get it back to original standard!
Regards, Barten
 
Hi.
Check the voltage before the switch which is permanently live.
Then measure what is coming out when horn switch used.
I managed to fix a similar fault by taking the switch appart and cleaning the brass contacts for the horn control, cheaper than a new switch.
Clive.
 
It is quite common for the contacts of the horn switch to burn out. Cleaning them will certainly help temporarily, but a proper relay is more of a long term solution.
 
Thank for the replies guys. I have taken the switch apart and cleaned it. It did not help much unfortunately. I was planning fit a relay, but tried it and it seemed that the 8,5 V that I got was not enough to trigger the relay.
 
Might be a good idea to also check that the earth connection is making a good contact. Any corrosion there will result in big voltage drops when under load.
 
What happens if you bypass the switch and using a piece of wire join the live in and switched output?
 
I have checked the original earth and it seems to be good. I have used it now with my new switch and el supply. I have not tried to bypass the switch and tried to connect a wire directly to the horn. I might try that. Are you saying the live feed is live also before the ignition is on?
Regards, Barten
 
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