Hella Marine 35A 12V Micro ISO Relay | 5-Pin SPDT

A relay is one of those parts nobody thinks about until they need one, and then it's the most important thing on the boat. The Hella Marine 965453801 is a 35 amp, 12 volt micro ISO relay with a single pole double throw contact set across five blade terminals. It lets a small switch control a big load, which is exactly what you want when you're wiring bilge pumps, light bars, horns, or any accessory that pulls more current than a dash switch should ever carry.

Here's the simple version. You run a light trigger wire to the coil, and the relay does the heavy lifting on the load side. That keeps the high-current path short and direct, protects your switches, and stops voltage drop from cooking a long run of undersized wire. Because this one is a single pole double throw unit, it gives you both a normally open and a normally closed contact. So you can switch a circuit on when the coil energizes, or flip a load from one path to another. That changeover contact is what sets it apart from a basic on-off relay, and it opens up some clever wiring. Think of a setup that defaults to one circuit and swaps to another when you throw a switch.

The 35 amp rating gives you real headroom for most 12 volt marine loads. Bilge pumps, wash-down pumps, LED light bars, electric horns, fuel pumps, and accessory circuits all live comfortably under that number. We always tell folks to size the relay above the actual draw of the load, not right at it, so the contacts aren't working at their limit every time they close. Check the current draw stamped on your pump or light, add some margin, and you'll get years out of it. And always fuse the load. The relay switches current, it doesn't protect the circuit.

Where does one of these actually earn its keep? A classic case is a bilge pump you want to run off both a float switch and a manual override at the helm. The relay lets the float switch trigger the pump without that switch ever carrying the full pump current. Another is a set of spreader lights or a light bar, where the relay carries the amps and your dash switch just sends the signal. Electric horns, macerator pumps, and livewell pumps all follow the same pattern. Any time the load is bigger than the switch wants to handle, a relay belongs in the circuit.

The micro ISO body is the compact standard you'll find all over modern 12 volt systems. It drops into any matching micro ISO socket or relay holder, which is the cleanest way to mount it. A socket gives you a tidy place to land your wires and lets you swap the relay in seconds if you ever need to, without cutting anything. The five blade terminals plug straight in. If you're building a panel or adding a bank of accessories, these keep the wiring sane behind the dash.

Hella Marine builds this stuff to their fit-and-forget standard, which is the whole point of buying a known brand for a part this critical. A relay that chatters or sticks is a headache you don't want three hours offshore. Still, treat it like any electrical component on a boat and give it a protected, dry spot to live. Behind the helm, inside a console, or in a sealed electrical box all work well. Keep it out of the bilge spray and standing water unless it's inside a proper enclosure.

Wiring is straightforward if you've done a relay before. The coil terminals take your low-current trigger, and the heavier terminals carry the switched load. Like all ISO micro relays, the terminal layout is marked right on the body, so check the diagram before you land your wires rather than guessing. One thing to know up front. This is a 12 volt DC part. It isn't meant for 24 volt systems or any AC load, so match it to a 12 volt boat. Get the right relay for the job and it just disappears into the background doing its work, which is the best thing a relay can do.