Fan Relay replaced with Bosch Relay... Can I remove old relay?

[CompassRDB]

I started to ask this question in a prior post before I had a better understanding of what the PO did (mind you better not perfect understanding)... I have traced the fan wires to a Bosch 0 332 019 150 relay which appears to been installed I suspect replacing the fan relay mounted in front of the engine... the Thermo couple wire is also run to this relay. The original Fan and Over ride Relays (the car had factory air since removed) are still wired in some way (need to further pull wiring apart to see how) but they are not connected to the fans or the T Stat (not sure if the thermo couple being used is or replaced the Otto Switch. Seems like they are not being used for any purpose and could be removed... sound about right?

An additional wire I am trying to figure out ... in addition to the Thermo couple wire, there is also another wire coming from the 2nd + on the Lucas 4TR Voltage Regulator and running to the Bosch Relay... It appears to also call for the fan to come on, but I am not sure under what condition it will do so. Can anyone help enlighten me?

Final question which has to do with the Lucas 4TR Voltage Regulator... PO installed a single wire alternator... there are two wires coming from the same pole from the alternator... one goes to the Bosch Relay and the Battery and the other one goes through the fire wall to ???? tomorrow project is to chase that one down. So my question is... if the alternator has a voltage regulator built into it (hence single wire)... do I still need the Lucas 4TR?

Thx

BB

[CompassRDB]

so another day of tinkering... Covid has provided me much time to spend under the Bonnet that would have been pushed to another time... so am enjoying the progress being made...

I reconnected everything this morning... tested on all components before starting the engine and she started right up! Fan and Over Ride relay sitting partially disconnected off to the side as is the AC wiring harness... the Bosch Relay kicked the fans on and off as before without any issues. Seems like I can at least try to disconnect the old relays and see if there are any unintended or expected consequences.

As I continue to clean up and detail the left hand side of the engine compartment... she's beginning to look like she did when first assembled. Good feeling.

I am sure I will have more questions as I dig deeper into her.

Hope you all are having a nice weekend!

BB

[mach2andy]

Hi BB
If you add details of your car to your profile, we'll know what vehicle we're talking about. It would also help if you explain the thermo couple you mention? Does your ignition warning light work? On a S2 car with the factory alternator, there is a relay secreted underneath the heater that controls this light. One of the outputs from the alternator is a 7v supply to this relay. Others have fitted single wire alternators, but I don't know how the ignition light is controlled with this arrangement. Perhaps this mystery wire through the bulkhead has something to do with this light? Some of us - me included - have wired a belt and braces switch to bring the cooling fans on in the event that the otter switch fails. Mine is hidden under the dashboard. Perhaps you'll find one on your car somewhere? Most of us on here have seen some pretty weird and wacky wiring on old cars from time to time, so whether or not you can remove the 4TR will depend I suppose on how the PO has rewired your car?
Andy

[johnetype]

BB,

The Otter switch in the radiator is notoriously unreliable so I suspect a PO has bypassed the Otter switch and the original fan relays with what you're calling the thermo couple and the Bosch relay. I would recommend that you replace the Otter switch with either a new one or a modern electronic equivalent from the likes of Cool Cats(?). You can then revert to the original relay (and or replacement if needed) and wiring.

The connection to the second +ve terminal on the 4TR unit to the Bosch relay is just a convenient place for the PO to pick up an ignition switched +12 volt supply for the Bosch relay, the fact that it's on the 4TR unit is irrelevant.

Your "single wire" alternator with its built in regulator does not need or use the 4TR unit. Nor does it use the alternator relay which you could repurpose as a spare fan relay if you need it.

The second wire you mention going from the alternator through the firewall probably goes to the ignition warning light in the speedo. If you look closely you should find that it comes from a different "pole" on the alternator - or at least it should - but they are right next to each other.

In reality you do not need to go back to the speedo to connect to the ignition warning light as you can pick up a connection to the warning light at the 3AW unit which is adjacent to the 4TR unit on the engine side of the firewall. It's the brown/black wire in the original wiring.

The 3AW unit looks like an aluminium 35mm film canister with a tab on it but as you don't need it or a 4TR unit to run a single wire alternator, it may have been removed by the PO but the wiring will still be there.

On a single wire alternator it is the ignition warning light feed that turns the alternator on and off so you need it connected. A single wire alternator actually needs two wires, plus ground which it gets through the alternator body.