Been working on my car this week and got a lot accomplished. New steering rack in, new hoses and belts, plugs and wires, rebuilt front brakes, bled all of the brakes and new seat belts. All went really well. Now I suspect my alternator is dead (the car has sit for 7 years) and will work on that tomorrow by seeing if its a brush issue. (I have a few new sets from the previous owner who told me they go all the time--it may have been the reason he parked the car 7 years ago?)
One weird thing I found running the car today is that when I turn the fan switch on the tach goes dead. Turn it off and the tach comes back to life. No other switch has any effect on the tack at all. I looked at the schematic and can't see how that can happen. Any ideas?
Steve
A weird electrical issue
#2 Re: A weird electrical issue
Steve,
the one thing the tach and the heater fan switch have in common is that they source +12V from the same fuse F7. I would check that the green wire from the tach is indeed directly connected to F7.
- Manfred
the one thing the tach and the heater fan switch have in common is that they source +12V from the same fuse F7. I would check that the green wire from the tach is indeed directly connected to F7.
- Manfred
1972 E type 2+2 Willow Green
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#3 Re: A weird electrical issue
Dear steve,
The implication is that either the 12v that the tachometer sees is reduced somewhat when the fans run, or that there is electrical noise which compromises the tachometer function.
I would clean all of the bullet contacts and switch contacts on the green wire circuits (and white wire before that feeds it and brown wire that feeds that) that share any run with that going to the tachometer.
You can verify that that is where the problem is by measuring the voltage on the green wire at the tachometer with and without the fan on whilst the engine is running.
The other thing that is needed for the tachometer to be reliable (depending on the model) is a good earth connection between it and the chassis.
If essentially you have too much voltage drop on the green wire to have a good enough supply to run the tachometer from it, consider inserting twin relays and using the fan green wires to power the relays only. The power for the fans proper can come from the brown wire. This would solve your problem as it'd isolate the tachometer from the fans in terms of electrical noise and it's also means the only voltage drop on that circuit would be for one relay coil winding, rather than that caused by a higher current sink like a fan motor run through some ropey old high resistance green wires.
kind regards
Marek
EDITed first para - it's a s3
The implication is that either the 12v that the tachometer sees is reduced somewhat when the fans run, or that there is electrical noise which compromises the tachometer function.
I would clean all of the bullet contacts and switch contacts on the green wire circuits (and white wire before that feeds it and brown wire that feeds that) that share any run with that going to the tachometer.
You can verify that that is where the problem is by measuring the voltage on the green wire at the tachometer with and without the fan on whilst the engine is running.
The other thing that is needed for the tachometer to be reliable (depending on the model) is a good earth connection between it and the chassis.
If essentially you have too much voltage drop on the green wire to have a good enough supply to run the tachometer from it, consider inserting twin relays and using the fan green wires to power the relays only. The power for the fans proper can come from the brown wire. This would solve your problem as it'd isolate the tachometer from the fans in terms of electrical noise and it's also means the only voltage drop on that circuit would be for one relay coil winding, rather than that caused by a higher current sink like a fan motor run through some ropey old high resistance green wires.
kind regards
Marek
EDITed first para - it's a s3
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#4 Re: A weird electrical issue
Manfred and Marek, thanks for the quick replies and suggestions. I'll get into it today and see if I can sort it out.
Happy New Year!
Steve
Happy New Year!
Steve
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