The Delay Relay has been number one on the electrical problem roster. It was designed to turn on the coolant fan when the car is stopped, only if the coolant temperature rises above a "critical" point; generally on super hot days, when the car runs the hottest. It was an attempt to cool down the system. However, it'd only cool the radiator fins and not really do a very good job of cooling the engine, since the water pump wasn't running with the engine off. So, it's not really that useful.
The real problem comes when you look at its design. It's an unsealed electronic module with a circuit board inside. And, it's located on the drivers side inner fender well, right in the line of fire for water to fall into it. And it does. Gets inside, damages the circuitry, turns metallic parts into rust. Ahd, here's where the problem kicks in. The rusted metal potentially falls into the electrical connections, causing shorts. Best-case, the short will keep your fan running all night, until your battery dies. Worst-case, the short will back-feed your fuse panel, keeping the car running even when you remove the key. I've seen it happen many times. Lots of guys replace their battery, alternator, and spend hours trying to figure out why the car battery dies overnight - only to find the culprit being the Delay Relay.
Fact is, the car is much better off without it. Since most of us have already replaced the factory 190 deg thermostat with a 160, and probably have already replaced the almost-dead radiator with a better one, you really won't see excessive temperatures in your cooling system anyway.
Earl Brown gave you some sound advice. Just wear safety glasses when you whack it with a sledge hammer.
Look at
http://www.installationinstructions.com/FYI/delay-relay.pdf for a repeat of what I just wrote.
