auxiliary water pump wiring

[jdere31760]

Hello to all,
Regarding auxiliary water pump wiring, using a power probe, I found the brown wire going to the pump grounded correctly. I checked for power on the black wire going to the pump and it was grounded, no 12 volt reading. With the pump disconnected from the electrical circuit, I was able to power on the pump with the power probe.
Checking the electrical diagram, I could not find the black wire.
Can anyone point me in the right direction?
Thanks
Joe

[Diesel911]

On the W123s the Aux Pump has no fuse in the circuit. If it for some reason pulls too many amps it fries part of the circuit board in the control inside of the Car. Once that frying cause someone's care to light on fire.

Look up in the Factory Service Manual when the Aux Pump can come on in normal use. I don't have that info but perhaps someone can give it to you or supply a site where you can see the manual.

[optimusprime]

Dont know what car we are talking about here ,,nothing in posters profile to say ..

[Mxfrank]

Originally Posted by Diesel911

On the WQ123s the Aux Pump has no fuse in the circuit. If it for some reason pulls too many amps it fries part of the circuit board in the control inside of the Car. Once that frying cause someone's care to light on fire.

I don't think that's true in all cases. At some point, a fuse was added, but it was inconveniently located on the back of the pushbutton unit. You had to pull it from the dash to replace the fuse. In any event, there's no indication that this is a 123. On the later cars, an automatic circuit breaker was added.


To the poster's question, power for the aux pump is supplied through the climate control pushbutton unit.

[jdere31760]

Originally Posted by optimusprime

Dont know what car we are talking about here ,,nothing in posters profile to say ..

Optimus, I have a 1985 300D.
Thanks

[jdere31760]

Originally Posted by Mxfrank

I don't think that's true in all cases. At some point, a fuse was added, but it was inconveniently located on the back of the pushbutton unit. You had to pull it from the dash to replace the fuse. In any event, there's no indication that this is a 123. On the later cars, an automatic circuit breaker was added.


To the poster's question, power for the aux pump is supplied through the climate control pushbutton unit.

MxFrank, should I pull out the climate control unit in order to find out why the aux pump I not being powered on?

[Mxfrank]

No, I'd start by digging up the appropriate wiring diagram so that you can do an informed diagnosis.

[Diesel911]

Originally Posted by Mxfrank

I don't think that's true in all cases. At some point, a fuse was added, but it was inconveniently located on the back of the pushbutton unit. You had to pull it from the dash to replace the fuse. In any event, there's no indication that this is a 123. On the later cars, an automatic circuit breaker was added.


To the poster's question, power for the aux pump is supplied through the climate control pushbutton unit.

You are the first time I have read that there is the Fuse you were speaking of.
There is at least 2 thread on the Pump that includes adding a fuse to the circuit.

When I went to add a fuse to mine I found out the Pump was dead and just left it disconnected. Not so cold where I live so you don't need it.

[Diseasel300]

Originally Posted by Diesel911

You are the first time I have read that there is the Fuse you were speaking of.
There is at least 2 thread on the Pump that includes adding a fuse to the circuit.

When I went to add a fuse to mine I found out the Pump was dead and just left it disconnected. Not so cold where I live so you don't need it.

He also mentions an auto-resetting "circuit breaker" on the later cars. Maybe on the 190 (which uses an entirely different control unit), but absolutely NOT on the W126 or W124 from 1986+.



Having repaired many W123 and 107 pushbutton units and silver control boxes, I've also never seen a fuse anywhere. Not saying they don't exist on those cars, they did some weird stuff throughout the 1985 year.

[optimusprime]

Best to fit a fuse in the hot wire to the donky pump . Stop it frying pbu

[Usaguy]

Originally Posted by Diseasel300

but absolutely NOT on the W126

I have a w126 2nd gen acc wiring diagram and on a 1986+ W126 the auxiliary coolant pump gets its power from fuse 6 (8 amp) in the fuse box and the acc is grounding the pump.

On 85 and older cars the pump gets its power from the acc and has just a regular ground but I can't find detailed acc diagrams for 85 and older cars to see if there's a fuse

[Diseasel300]

Originally Posted by christuna

I have a w126 2nd gen acc wiring diagram and on a 1986+ W126 the auxiliary coolant pump gets its power from fuse 6 (8 amp) in the fuse box and the acc is grounding the pump.

On 85 and older cars the pump gets its power from the acc and has just a regular ground but I can't find detailed acc diagrams for 85 and older cars

The 85 and older cars are fused through the ACC fuse as well. The problem is that a seized pump can burn out the printed circuit board in the pushbutton unit.

The 1986+ models use a darlington transistor pack to switch the pump on and off. When the pump goes bad or shorts internally, it burns out the darlington pack (which is NLA with no modern replacement) or it burns open a power trace on the printed circuit board. I've repaired close to a dozen of all 3 major revisions of these boards and I can assure you, there is no "circuit breaker" anywhere in there.

[Mxfrank]

Originally Posted by Diseasel300

The 85 and older cars are fused through the ACC fuse as well. The problem is that a seized pump can burn out the printed circuit board in the pushbutton unit.

The 1986+ models use a darlington transistor pack to switch the pump on and off. When the pump goes bad or shorts internally, it burns out the darlington pack (which is NLA with no modern replacement) or it burns open a power trace on the printed circuit board. I've repaired close to a dozen of all 3 major revisions of these boards and I can assure you, there is no "circuit breaker" anywhere in there.

From the '87 Tempmatic supplement for the 190. It may be that the 300SD was less sophisticated:

[Diseasel300]

Originally Posted by Mxfrank

From the '87 Tempmatic supplement for the 190. It may be that the 300SD was less sophisticated:

123, 124, 126, and 107 chassis do not use the Tempmatic system. That is exclusive to the 201. You cannot compare the 201 system to any other chassis, the control scheme shares little in common with the ACCII and ACCIII systems in the aforementioned chassis.

[jdere31760]

Thanks guys for all the info.
Should I look into my ACC unit to see why the black wire is grounded or should I just replace the ACC? Sometimes when I am warming up the 300D, the ACC unit starts to rattle and after a few minutes, it stops.
I am also thinking I can just bypass the ACC and power up the auxiliary pump since it's not seized but I will need to find another circuit to tap into.
It's unbelievable how many items on this car still don't work or is leaking, I have been trying to solve one issue after another.