What is this relay on the firewall?

[jangell]

Just curious: on my car, there's a relay on the firewall that appears to supply the ignition system resistor. I couldn't find it in the manuals, although I may have simply overlooked something.

The reason I'm interested is that my car stalled at a gas station today and refused to start. A mechanic happened to be there, and we determined there was no spark. He then traced the wire from the resistor to the relay. He pulled the relay, banged it, plugged it back in and the car started right up.

I've replaced the relay with a new one (the old one was a metal Bosch one), but I'm still curious about what it's for and where I'd find it in the manuals. It's the black relay on the left side of the picture.

Thanks!

-- Joe

[DMC5180]

Ignition Resistor By-Pass relay. It is only energized while the starter is engaged. It sends full voltage to the coil for easier starting. It was an after thought "fix" in production and didn't make it into the manual or electrical diagram

Sometimes the terminals on the resistor get loose or corroded which can cause a no start situation.

[jangell]

Ah. That doesn't explain why I stalled (I started the car at the gas station, touched the gas and it stalled out), but it does explain why it wouldn't start again. Thanks!

-- Joe

[David T]

The terminals on the ballast (white) resistor are steel. They rust and then the wire connectors do not make good contact. By banging, touching and otherwise disturbing them it may seem to "fix" it. The best thing to do is to remove each wire, one at a time, and clean the terminals on the ballast resistor with a wire brush or some sandpaper to get the terminals clean and shiny. The ballast bypass relay is not all that important but it should work.
David Teitelbaum

[Bitsyncmaster]

The terminals on the ballast (white) resistor are steel.

I think they are stainless steel. I could not solder to them. But I agree that it most likely was a bad connection on the resistors and when the mechanic traced them the connection got better.

[Bill Robertson's Sock Puppet #1]

You are correct -- the ballast resistor tabs are stainless steel and do not rust. Neither do the quick connects (tin coated copper). Connections can get loose and dirty, but not rusty.

The ballast resistor bypass is actually quite important for starting. If it fails you can emulate the circuit with a temporary piece of wire and touch the jump start post (not a permanent connection -- only while cranking).