Wiring

[h_m_cumming]

Temp. s/w and override

Here's an interesting one for you.
A simple circuit, two switches in parallel fed from a fuse from battery +, leading to the radiator fan then earth.
One switch is an on/off used as the fan override, the other a temperature switch in the top hose.
The override switch is the type with an internal light and contacts, live, accessory, earth.
The previous temp. switch was one which had the bulb under the top hose and the rad. tube. When it failed I decided to fit an adaptor in the top hose with a conventional thermal switch.
Before it failed everything worked perfectly, fan would cut in as require and you could override with the switch.
Fitted the new adapter and switch and wired it all up. Switch the override on, fan runs and switch lights up. Simulate the temp. switch working by shorting the contacts - fuse blows.

Checked, double checked and couldn't find anything wrong with the wiring.
If I disconnected the override switch fan would run when the temp. switch contacts shorted.
By now getting frustrated, so had a beer and slept on it.

My mind must have been dwelling on it because I had an Eureka moment.
The override switch must be the fault so I took it off and checked the terminals.
Live to accessories opened and closed OK. With the switch on acc. , to earth bulb resistance, with the switch off acc. to earth DEAD short.

I couldn't believe it and tested some other switches of the same type I had and all the same.
Removed the earth from the switch and all working OK.
With the old setup the temp. switch was fed from another live so didn't short when the switch was in the off posn.

So if you're using this type of switch in a parallel situation don't feed them from the same live.
You live and learn, sometimes.

I can see the next winter job is a rewire of the car as after 29yrs and many mods. to the wiring it's a bit of a rats nest.

Hugh

[listerjp2]

Re: Wiring

What can I say, my nemesis.

Hate bl***y electrics

Good luck

Adrian

Temp. s/w and override

Here's an interesting one for you.
A simple circuit, two switches in parallel fed from a fuse from battery +, leading to the radiator fan then earth.
One switch is an on/off used as the fan override, the other a temperature switch in the top hose.
The override switch is the type with an internal light and contacts, live, accessory, earth.
The previous temp. switch was one which had the bulb under the top hose and the rad. tube. When it failed I decided to fit an adaptor in the top hose with a conventional thermal switch.
Before it failed everything worked perfectly, fan would cut in as require and you could override with the switch.
Fitted the new adapter and switch and wired it all up. Switch the override on, fan runs and switch lights up. Simulate the temp. switch working by shorting the contacts - fuse blows.

Checked, double checked and couldn't find anything wrong with the wiring.
If I disconnected the override switch fan would run when the temp. switch contacts shorted.
By now getting frustrated, so had a beer and slept on it.

My mind must have been dwelling on it because I had an Eureka moment.
The override switch must be the fault so I took it off and checked the terminals.
Live to accessories opened and closed OK. With the switch on acc. , to earth bulb resistance, with the switch off acc. to earth DEAD short.

I couldn't believe it and tested some other switches of the same type I had and all the same.
Removed the earth from the switch and all working OK.
With the old setup the temp. switch was fed from another live so didn't short when the switch was in the off posn.

So if you're using this type of switch in a parallel situation don't feed them from the same live.
You live and learn, sometimes.

I can see the next winter job is a rewire of the car as after 29yrs and many mods. to the wiring it's a bit of a rats nest.

Hugh

[scott h]

Re: Wiring

The fan should be wired through a relay because the high load will destroy most fan switches. The earth from the relay is wired through the fan switch, a manual overide can be spliced to this wire and also connected to earth. Then if either switch completes the earth circuit the fan comes on.

[h_m_cumming]

Re: Wiring

Checked the current draw, kicks 7A on startup runs 4.5A which is well within the capabilities of both switches.
My problem was the override switch shorting to earth when switched off. I opened it up to have a look and see if it could be modded but is one of these where any interferrance wrecks the switch, so I just do without the light in the switch for now. Will fit a separate light later. I've powered it direct from the battery, through a fuse, so that the fan will run when the ign. goes off to cool down the rad. and under the bonnet.

[element]

Re: Wiring

I might have something similar going on with my headlights switch; it's a rocker switch. The other week when it was a little dim, I put the lights on and while driving home could smell a distinct electrical burning rubber / plastic smell. Switched lights off - smell disappeared, on and it came back again. Fortunately, I don't drive it in the dark; only dry sunny days (of which there has been plenty this summer ).
I figure the best set up would be as suggested - through a relay - though I have zero experience of relays; I'll get around to it before long.

[stevejgreen]

Re: Wiring

I might have something similar going on with my headlights switch; it's a rocker switch. The other week when it was a little dim, I put the lights on and while driving home could smell a distinct electrical burning rubber / plastic smell. Switched lights off - smell disappeared, on and it came back again. Fortunately, I don't drive it in the dark; only dry sunny days (of which there has been plenty this summer ).
I figure the best set up would be as suggested - through a relay - though I have zero experience of relays; I'll get around to it before long.

Wharever you do, don’t let the smoke out.

Here or There

[Blue Marlin]

Re: Wiring