Let's talk relays

[Slick68]

I'm usually pretty good at wiring, but relays seem to be my downfall. I just can't seem to understand how they work. Anyway, what would cause a relay to go bad? What would some symptoms be?

I'm fighting an issue with the 6014 MSD timing control box in my C10. It wants to cut timing to the driver's side coils after two or three run cycles. I can disconnect the battery for a few hours, hook it back up and it will run fine for another 2 to 3 run cycles and start all over. I've currently replaced the box, and the wiring harness for the system(new harness came with warrantied box). Per the instructions, I installed a 30Amp relay when I first installed everything last year. Before I even attempt to hook up a battery and restart, the only part I haven't replaced is the relay. I'll go pick up a new relay soon and replace, but I wanted to ask the electrical experts if this sounds like something a bad relay would cause.

[blitzer454]

I would say that there are two types of failures that are common for relays. One is the relay contacts can stick together because of the arcing that can occur each time the relay is activated. The other common problem is that the relay coil can open. But in your case I suspect that the relay is not the problem as this wouldn't cause a problem with just half of the cylinders not working. I would look for things that are in common to the driver's side coils, like the ground wire for that side. Is connected to a good ground and is the terminal good and clean? Maybe try using a star washer to make a better connection. Good luck!

[andrewb70]

I just can't seem to understand how they work...

Relays are just electronically activated switches. They are used to power a device and are generally placed closer to both the power source and the device than a switch would be.

Think about a classic headlight switch. It has multiple big gauge wires. Power is transmission from the battery, to the fuse panel through the switch, then back out the the headlights. A more modern arrangement would be power is taken from the battery, goes through and under the hood power distribution point (a fuse box and relay center), then to the headlights. The relay is then powered by the headlight switch and the wires can be very small, since triggering the relay does not draw a lot of current.

Andrew