What is the reason for having a starter relay?
 

Hi everyone,

I'm a self-employed mechanic, and today I had to work on a 1995 Acura Integra LS. The ignition switch wouldn't engage the starter when you turned the key.

I narrowed it down to a defective 4-pronged starter relay mounted under the dash, located to the left and up of the driver's side fuse panel.

From my understanding, relays exist to allow a lower-current circuit to open or close a higher-current circuit. In the case of the ignition switch, having a starter relay means that the ignition switch no longer needs to be designed to carry 100% of the current that the starter motor requires. This allows for both a cheaper ignition switch design and thinner wires going to the ignition switch. This saves Honda money and everyone is happy.

But I'm just as perplexed, because all 4 wires going into and out of the starter relay are exactly the same gauge and therefore can handle the same amount of current. What is the point of this relay then?

Today, Advance Auto Parts (the only auto parts store in this tiny town) couldn't find the relay, so I made a temporary fix:

Ignition Switch --> Clutch Switch --> +12V Starter Terminal
(--> denotes a wire)

In doing this, I preserve the exact same functions that the starter relay used to perform. The starter motor will engage as long as this circuit is closed (depressed clutch + key turn). This fix worked as expected, and the customer can now use his car again.

Can someone enlighten me as to why this relay existed in the first place? Thanks a bunch in advance!

Nobody has any ideas? Surely there's a reason why Acura installed this relay, but I can't think of why. Should I consult an electrical engineer?

Bump.

Starter relay
 

They exist to keep the higher voltage or amperage away from the switch. The switch can be made lighter duty and therefore cheaper.

Also, additional circuits can be controlled by the relay thus simplifying the starting procedure.