This week end I was working on putting a main relay kill switch in a friends car. On the main relay I cut the two ground wires soldered them to a 16g wire and ran to my switch. The other side of the switch I ran to a common ground. (About 3 feet away). After completed I tested the switch. with the switch off the car cranks but doesn't start. With the switch on the fuel pump kicked on but still no start. So testing the two wires I cut using an ohm meter. I got continuity to ground on the one wire but the other on I got about 7 or .7 (can't remember) ohms of resistance. I spliced that wire back into the main relay and only ran the one i got ground on to my switch. Viola, the switch works perfect. My question is why did this happen? Also the switch I am using temp. is a lighted switch. When cranking the motor with the switch in the off position the light on the switch illuminates. How is that possible when I'm using a low voltage ground!? ha ha. Hopefully someone can answer that question.

 

One of the black leads going to the PGM-FI Main Relay is the ground, [from chassis ground point] the other black lead is a ground for another component in the car, when installing a kill switch on the ground for the PGM-FI Main Relay, cut both leads, connect the two leads on harness side together to one side of switch, do the same for the two leads from the PGM-FI Main Relay and connect to the other side of switch, or you can use just one of the leads from the PGM-FI Main Relay.

Doing it like above will allow you to use a smaller, [1A] easly hidden switch. 94

 

Everything works fine the way I did it so the way I did it above is fine? Also, still wondering why I'm getting a small amount of voltage from the relay ground. Thanks for the reply.

 

When the switch is open, [off] you will read 12V+ on the relay side of switch because the other side of relays, [fuel injection relay] coil has 12V+ going to it. 94

 

OK now I'm confused . why would I need a 12v relay for a low voltage ground. Everything is working how it should I was just wondering why i was getting voltage back on the ground when cranking the motor. I was assuming that the ground that I was getting resistance on was part of the ignition switch and by craking I was completing the circuit to ground.

 

You do not need a relay for a low voltage ground.

I was explaining why you are "getting voltage" on the ground lead. the relay I refer to is the fuel injection relay in the PGM-FI Main Relay, one side of relays coil, [#85] has 12V going to it, the other side of relays coil, [#86] has the ground, [you cut and installed switch on] lead on it, when that ground lead is not grounded it will test as 12V+, you are reading the 12V+ on the other side of the load, [the coil].

On a DC circuit if you test the ground side of a load when not grounded it will test as 12V+ if you test the 12V+ side of the load when 12V+ is not going to it it will test as a ground.

It is the same if you unplug the door pin switch and test the lead, it will test as 12V+ because the other side of dome light has 12V+ going to it, yet if you ground the lead it is not a short because of the load, [the dome light]. 94

 

I was just sitting here watching TV and it just popped in my head why I was getting voltage ha ha. Was logging on to say that i understood what you meant. Thanks a lot.

 

Your measuring the impedence of the relay coil.

The car is trying to activate the relay so it will start. Since you have a switch in there preventing the connection it's activating the light.