Starter relay question
 

Please don't get me wrong. I am not saying starter relay is bad but I want understand more about it.
1- Is there a chance the relay go bad by shorting the power and the signal, making the starter to start all the time (as you are holding your key at starting position all the time)?
<b>2- what relay rating I should use. I usually see relay out there at 12v 25A. Will 25A is good enough?</b>
3- Should I install a fuse on the power wire to the relay, or on the signal wire to relay, or on the power wire from relay to the starter?
Thanks.

anyone?

The starter solenoid mounted on the starter motor is the relay. The solenoid performs to functions: it switches large current (battery to motor) using a low current control circuit and moves the pinion gear into contact with the ring gear.

An auxiliary relay will only help if the existing control circuit from the ignition switch (yellow wire) isn't providing the correct source voltage to the solenoid (dirty ign. switch contacts, dirty/loose connections).

Here's a link to my external relay. I installed it along with a remote start switch to prolong the life of my ignition switch which is NLA.

Hope this helps,
Sherwood

so a normal 25A relay is good enough huh.
Thank you.

Yep. The relay only carries solenoid current, not starter motor current.

Sherwood

Thanks Sherwood

I hooked up a starter relay as provided in the Bosch WR-1 kit. In fact, 911pcars, the link has a pictorial drawing of the wiring diagram that exactly matches what was provided with the kit.

http://forums.pelicanparts.com/showthread.php?s=&threadid=340184&highlight=thermo time

I hooked it up exactly as shown on my '75 911. The only switched source is the existing ignition switch - no additional switches were added. This was done in conjunction with pressure testing the CIS.

But to my surprise, when I disconnected the Air Flow Sensor Contact on the Air Sensor Plate to get the fuel pump to run without the engine running, the starter engaged! This also occurred when I lifted the Air Sensor Plate arm from within the airbox.
I crawled back under the car and disconnected the relay, hooking the yellow wire from the ignition switch back up to terminal 50. Now the fuel pump was activated properly when I disconnected the Air Flow Sensor plug.

With my wiring diagrams, I am at a loss on explaining this. Needless to say, the relay is at the moment disconnected.