Symptoms of a faulty main relay:

Problems starting the car, usually after a short run (when the interior is warm), though in some cases, the car may fail to start at any time. A classic time for the problem to occur is at the gas station, or if you park for a minute to get something from a shop. If the car is parked for a long period, the interior usually has cooled enough for the joint to make contact again, and you won’t notice a problem. As the cabin temperature is a major feature of this problem, it might appear worse on cold or rainy days when you have the heater running to clear the windows etc. Extremely cold temperatures can also cause the problem to be more apparent.

FYI, The Main Relay controls five circuits:
Battery
Ignition
Pump
Injectors
Starter

Reason why car won’t start:
The main relay wouldn’t fire up the fuel pump due to the soldering cracks on the Relay PCB.
Cracks would appear over time and can be re-soldered, or you can buy a new one from the dealer. Im cheap, so I’d fix it. LoL

Here’s a closeup of a bad main relay solder joints:

MAIN RELAY LOCATION:
On most Honda’s the main relay is usually located under the dash on the drivers side,
in or near the fuse box area and due to its size is quite easy to find.

MAIN RELAY REMOVAL:

The steps below show removal of the relay from a right-hand drive 88-91 CRX, however the steps are exactly the same for the left-hand drive model.

Tools Required:
Cross-head screwdriver.
10mm Socket.
Extension bar for above.
Ratchet for above.
10mm Ring spanner (preferably ratchet type).

1. Remove the hood lever with a 10mm socket and extension bar. There are two bolts, the bottom one is being removed in the picture. When the bolts are out the level will fall out of the way.

2. Remove your fuse box cover to gain access to the coin holder. Now remove the coin holder – spring it open and you will see two screws at the top and one at the bottom. When the holder is out of the way we can see the top of the relay.

3. The bolt securing the relay is well hidden, you can access it from the directly above the hood lever. The bolt is impossible to see unless you get your head in the foot well so just use have a feel for it.

4. A ratchet spanner greatly speeds up removing the relay although it is possible with a normal ring spanner but it will take a few minutes. DO NOT try to use a open-ended spanner as you will probably round the bolt! Only use a ring-spanner if you do not have a ratchet one!

5. With the bracket loose we can now lift out the relay. Along with the bolt, the bracket is hooked with a tag so you may have to wiggle it a bit to free it off or it might just lift straight out.

6. The relay will now lift out – it is fitted with a long lead so you can easily get into the connector, and unplug it.

Re-installing the main relay back in is the reverse of removal, however getting the bolt
back in can be a little tricky. Remember to slot the notch on the relays bracket back into
the hole on the car as this will hold the relay in the exact position for the bolt to go in.

MAIN RELAY REPAIR:

Repairing your main relay is very simple, and requires only a few tools:

– Soldering Iron, powered around 25w is fine.
– Good Quality Solder.
– De-soldering tool – pump style, braid or de-solder station if you are lucky.
– Stiff toothbrush
– (Isopropyl Alcohol) cleaning Solvent

1. Bend back one of the retaining clips and lift up one side of the relay, then repeat with the other side.

2. The relay should now be free from the housing. ( lifted out )

3. Slide the relay PCB board from the housing. Note that it only fits one way.

4. Now you have to remove the old solder from the board. I recommend you only de-solder and re-solder one connection as a time as there is a chance some of the components may fall out the board inside the relay requiring it to be dismantled.

5. Now re-solder the connections making sure you use enough heat to fully flow the joint – compare your joints to the picture. They should have a shiny finish. If the finish on your joints is dull, you are probably using a poor quality solder, or not enough heat.

6. Next you can remove the flux from the board. This isn’t strictly required but it’s nice to finish the job properly. Spray on plenty of Alcohol solvent and use the brush to remove the flux, you may need to do this a couple of times to get rid of it all. This will make a bit of a mess.

The relay can now be clipped back into its housing and reinstalled to the car.