1989 Ninety heater oddity.

A

Anaconda

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Thames Valley

• Feb 27, 2025

• #1

My son has been mentioning the heater fan doesn't work. I have been faffing around with it a bit with the ignition on, I can't get it NOT to work?
Turns out it works fine with ignition on but not when the engine is running.
Going to clean the fuse holder when I get a chance, any other ideas?

 

tottot

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west wales coast

• Feb 28, 2025

• #2

Note that is an odd one, if switched on should go at all times the ignition is on regardless as you know.
All I can think is some one has wired it wrong at some time but just a guess.

 

Last edited: Feb 28, 2025

A

Anaconda

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Thames Valley

• Feb 28, 2025

• #3

tottot said:

Not that is an odd one, if switched on should go at all times the ignition is on regardless as you know.
All I can think is some one has wired it wrong at some time but just a guess.

Click to expand...

The wiring looks stock and it's worked fine for years. I'm thinking must be a loose connection somewhere which might be affected by the vibration of the engine maybe.
Job for another day I think.

 

A

Anaconda

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• Mar 11, 2025

• #4

On a quick look this plug goes to the heater fan I think?
So for diagnosis can I use the green wire for a live and black for earth?

 

A

Anaconda

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• Mar 24, 2025

• #5

As usual the problem is in the least accessible part, inside the heater box.
I used wire wiggling and bashing things as part of my diagnosis. Bash the heater box and it will work.

 

julianf

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Devon, UK

• Mar 24, 2025

• #6

If it only runs when other stuff is off, could it be that the fan motor is trying to ground though somthing that is being pulled "high" when the other stuff is running?

I would start by running a temporary ground from the heater, to a known good point, and seeing what happens.

 

A

Anaconda

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• Mar 24, 2025

• #7

julianf said:

If it only runs when other stuff is off, could it be that the fan motor is trying to ground though somthing that is being pulled "high" when the other stuff is running?

I would start by running a temporary ground from the heater, to a known good point, and seeing what happens.

Click to expand...

It will run with the engine running if you bash the heater box,, poor connection inside most likely.
I will try a separate earth at some point before the heater box comes out.