Question concerning putting relay on starter circuit

[Pazuzu]

Bear with me...

I have put a relay on the starter circuit of my heavily rewired car. I have no problem with this by itself, and it works great.
However!
I'm having trouble with how it interacts with the A/C circuits via the yellow wire.

The factory setup (ignoring extra things like TTV and cold start stuff) looks like this:


Power to starter solenoid comes from the battery, through switch on dash, hot in Start only, and powers the solenoid. The yellow wire also acts as a ground sink for the A/C relay, and opens the relay when the ignition switch is turned to Start. We all know how this works at this point.

I have rewired thing as follows:


New relay feeding the starter solenoid, triggered by the yellow wire. Works great, EXCEPT!!

The A/C relay sinks the +12V on run into the yellow wire. Stock, that system feeds basically no amps and something less than +9V, and the starter solenoid simply ignores it (acts as ground). My new wiring however sinks that A/C relay into ANOTHER relay, and the nearly zero amps and low voltage is enough to trigger that relay.

Basically, wired like this, my starter solenoid fires up whenever I'm in Start OR Run.

Currently, my A/C is being worked on, so I have simply removed the yellow connection the A/C relay for now. That separates the two circuits and solves the problem.

So, how to fix this?
Is it possible that having the starter fed via a relay will make it strong enough that it can overpower the A/C clutch, in which case, I can remove that "A/C kill" setup when the key turns to Start?

Should I put a resistor on the yellow wire next to the A/C relay, hoping to drop the voltage out of the A/C relay low enough that the starter relay won't trigger?

Thanks all!

[mpetry]

Mike, I had the same problem - the starter basically did not disengage.

I just left the relay off the car and went to a "lightweight high torque" starter sold by our host.

I think the only way you could address the problem with the relay not unlatching is to run a separate starter button and wire the relay to that, not the "run" terminal on the keyswitch.

[Algernon]

I think you will cure the problem if:
Change the feed to the AC relay (pin 85) to come from the starter. That is, from new relay pin 87.
Don't change anything else, LEAVE the yellow feed from "+12v on start only" to new relay pin 86.
Algernon
BTW, where did you physically put the new relay? If it is hidden, it could be used to make a theft-proof hidden starter-kill switch!

[Pazuzu]

Originally Posted by Algernon

I think you will cure the problem if:
Change the feed to the AC relay (pin 85) to come from the starter. That is, from new relay pin 87.
Don't change anything else, LEAVE the yellow feed from "+12v on start only" to new relay pin 86.
Algernon
BTW, where did you physically put the new relay? If it is hidden, it could be used to make a theft-proof hidden starter-kill switch!

I think you're right! I can piggy back a connection at 87 on the starter relay, and send it back to the A/C relay...

Right now the starter relay is mounted on the engine itself. I have an extra heavy cable between the starter and the relay, a heavy cable between the relay and the solenoid, and thin low power cables going out to the engine bay via Weatherpack connectors. I did this so that I could take the strain off of the factory wiring, off of the Weatherpack (which has a limit of 20amps per pin), and lets my old starter turn over instantly, even when it was exhibiting hot start issues constantly.

I do plan on integrating some sort of kill switch, as well as a starter bump button that I can have in the engine bay.

[911pcars]

I agree with Algernon. Connect source voltage to the A/C relay (@85) from term. 87 on your remote starter relay.

FWIW, a remote relay on my early 911 (w/o A/C):
Remote Starter

The schematic in the link describes another cranking switch (.e.g. in engine compartment).

Sherwood

[Pazuzu]

Originally Posted by 911pcars

I agree with Algernon. Connect source voltage to the A/C relay (@85) from term. 87 on your remote starter relay.

FWIW, a remote relay on my early 911 (w/o A/C):
Remote Starter

The schematic in the link describes another cranking switch (.e.g. in engine compartment).

Sherwood

It's really the A/C that causes the problem, I assume that most of the cars have that run something like a starter relay have deleted the A/C, but not me.
I am also surprised/startled by the fact that Porsche (yet again) does something like dump amps through a sink like the starter system. Basically, it appears that the solenoid is semi-electrified the whole time you're driving, just not enough to trigger. No wonder we all have hot start/no start issues!

[911pcars]

Originally Posted by Pazuzu

It's really the A/C that causes the problem, I assume that most of the cars have that run something like a starter relay have deleted the A/C, but not me.
I am also surprised/startled by the fact that Porsche (yet again) does something like dump amps through a sink like the starter system. Basically, it appears that the solenoid is semi-electrified the whole time you're driving, just not enough to trigger. No wonder we all have hot start/no start issues!

All/most relays have a live source voltage wire connected to it. However, not energized, i.e. the source (power) circuit is open. Only when the control circuit (signal) is activated does the relay energize and complete the power circuit to the intended load (A/C compressor or other device).

A faulty relay (internal short) can bleed current to ground and reduce source voltage to other branch loads on that circuit. In the case of the starter circuit, reduced signal voltage to the solenoid can prevent it from energizing resulting in a no-crank starter situation.

S

[Algernon]

Where do you choose to put the relay?
Under the dash is easy, but if incorporating an anti-theft switch, maybe there is a better spot.
What is the route of the yellow wire from the "start" switch to the starter? Does it go down inside the tunnel? Or maybe under the car?
Somebody must know!
Bentley never tells you useful stuff like this!
Thanks,
Algernon.

[911pcars]

Originally Posted by Algernon

Where do you choose to put the relay?
Under the dash is easy, but if incorporating an anti-theft switch, maybe there is a better spot.
What is the route of the yellow wire from the "start" switch to the starter? Does it go down inside the tunnel? Or maybe under the car?
Somebody must know!
Bentley never tells you useful stuff like this!
Thanks,
Algernon.

See my link at #5 for a suggestion.

S

[Algernon]

Originally Posted by 911pcars

See my link at #5 for a suggestion.

S

yup, seen #5, but still looking for routing after dash so that the relay and an additional 'kill' switch can be less easily spotted.
I'm hoping it goes down the tunnel, so I can work on it from the access plate in front of the back seats, and hide the switch under the carpet.
Has anyone traced where the yellow wire goes??
Thanks, Algernon

[911pcars]

Originally Posted by Algernon

yup, seen #5, but still looking for routing after dash so that the relay and an additional 'kill' switch can be less easily spotted.
I'm hoping it goes down the tunnel, so I can work on it from the access plate in front of the back seats, and hide the switch under the carpet.
Has anyone traced where the yellow wire goes??
Thanks, Algernon

Click on one of the cleverly-disguised linked photos to see the relay in the rear tunnel, next to the shift coupler.

As for a hidden kill switch, one suggestion is to disable the fuel pump to kill the engine. Install a series SPST switch (toggle, rocker, push button, etc.) in an extended section of the fuel pump circuit. Your secret location could be under the seat, next to the parking brake, under the dash or even disguised as a factory switch for an electrical option not equipped on your car (e.g. sunroof, rear wiper, etc.)

S