I have a basic understanding of electronics, which means I have learned to ask for help when I'm in over my head.

I have been using a programmable output from my MS2 Enhanced (Thanks, Rev) to run the steering pump after the engine has started, to mitigate electrical load on the system.
My new setup dictates I must use said programmable output for something else.

I had tried - unsuccessfully - to tap the L terminal of my alternator to trigger a relay, so that the PS pump would run only after the alternator had started charging.
(For the record, I have an LS terminal setup, instead of the ECU controlled PD alternator scheme normally seen in Miatae.)
In my case, "L" is the terminal that gets 12V on it when the alt starts charging - it is connected to the charge light in the dashboard.

Powering a relay from the L terminal causes a major voltage drop, which in turn causes the charge light to come on.

Is there a way to tap the L terminal (for a relay) without causing a voltage drop?
I know they sell al sorts of ready made circuits for different purposes. Would I be able to find such a circuit? And what would it be called if there is one?
I don't even know what to look for... .

Thank you.

 

The alternator isnt always at 100% load so that might cause problems.. isnt it just better to hook it up to the ACC on?

 

You may try running off the 87A contact of a relay that is triggered by the battery light output instead. On the Enhanced MS2, the battery light comes off a few seconds after the engine starts. Make sure you trigger the battery light itself from the 87 contact (30 to ground) so that you don't overload the output of the ECU (which was designed to run a single light bulb, not a bulb AND a relay). Also, add a zener diode to the output as there's no flyback protection on this bulb output.

 

So, in order for this scheme to work, I need tun alt control on then.
I have it turned off currently.

Since my alt runs independent of the MS, will it hurt anything to turn alt control on?

 

No, it won't hurt anything.

 

One other option would be to buy an RPM switch. You feed it a tach signal, program an RPM into it, and when it rises above that set value it closes a switch. Set it to 500 RPM and it'll run whenever the engine is running.

Similar to this: https://www.summitracing.com/parts/sum-830452-1

--Ian

 

So my electric (assisted) power steering started acting up a couple days ago.

It just quit.
Then it came back.
Then it quit again.
Then came back for no apparent reason.

I thought it could be the octocoupler. It is connected to the sense wire at the alternator, so it runs once the alternator starts charging. (I have a different alt setup)

So I tore into it tonight.

Octocoupler triggers a relay, and that relay triggers a pretty heavy 70 Amp relay, which closes the ground side of the motor (Unswitched, fused power comes from the battery)

Sure enough, there was a bit of oxidation on the octocoupler connections. I cleaned everything and proceeded to bypass it for further testing. Motor would not run.
Checked both relays, just fine.
Checked power, battery voltage is present.

Manually grounded relay output, motor does not run.

So I pulled the motor and tore it apart. Sure, there is some wear and dirt on the brushes, but seems OK.
Meticulously cleaned and serviced the motor. Bench test, it runs!

Installed the motor on the pump, hooked everything up, motor does not run...
Tap on the motor in frustration, runs and stops...

Took the motor apart again, checked everything, runs on the bench.
Motor refuses to run in the car...
Checked for voltage again and again, battery voltage is present.

I said the hell with it, and hooked up a long heavy wire from the battery + to the motor, damn thing ran.

After a light bulb moment, I checked the motor wire connector on the battery post.
Damn thing had corroded to a point where a single strand of the heavy wire was barely conducting anything anymore.
Just enough to show me voltage, but not capable of carrying any current to spin the motor.

A brief moment of heavy cursing was followed by replacing the battery post terminal with a heavy duty one, careful application of weatherproof shrink tubing to avoid future headache, and cleaning all electrical connections...

It runs beautifully once again.
Yeah, simple repair.

 

Reminds me of the intermittent non-start issue I had with my '93 L.E. (although it ultimately took me years to discover the root cause). I replaced starter motors (more than once), the ignition switch, installed a relay (in case the ignition wiring was getting tired), added additional grounds and even completely replaced the positive cable from the battery to the alternator. I even changed out the battery, just in case. In the end, it turned out to be the clutch interlock switch, which was failing. I didn't even consider it as a suspect because it was supposed to be always off, with the FM-supplied U-clip holding the plunger permanently in. Before the problem was fixed, I was seriously considering just walking away from the car, as it wasn't any fun driving it anywhere when there existed a likelihood that I wouldn't be able to get home again. Glad you discovered your root cause in a more timely manner.