to repair the Main Relay.
The relay's solder
joints dries, crack and separates from the circuit causing an
open circuit. The joints is subject to heat generated by the
fuel pump. The joint is then allowed to expand and
contract and subject to vibrations. For this repair project you will need a:
watt soldering iron and
a Rosin core
solder (higher silver content
a solder wick or
a De-soldering pump
To Desolder: Tool required: vacuum
pumps (solder suckers) or solder wick.
To Solder: Tools required: a
15-30W soldering iron and thin rosin core solder.* Here's
more soldering examples.
Many people chose a higher grade solder
with a higher silver content (Radio Shack) to minimize the chance of a cold solder joint.
by prying open the main relay:
Stick a flat small flat screw driver in between.
- Stick a small
flat head screw driver in between the wall flap (a clip) and the
- Do not go
in too deep. Pry it open just slightly
- While holding
it still, use the same screw driver, pry the other side.
- While holding
it still (and cleared of the locking edge) pull the relay straight
out, or forward.
Do not stick the screw driver too deep inside. You may damage the relay's
mechanical or electrical parts.
Quick Step 1:
Desolder the relay lead.
Desolder using pump
Desolder using wick
Heat lead with a soldering tip while applying rosin core solder to the component lead and solder pads.
3: Clean with steel wool, inspect for imperfections then coat
with lacquer to prevent oxidation.
4: Install onto the vehicle in a lower location, easily
accessible in the future. You work is done.
When a fuel pump demands more current, heat would be generated as a result of
increase resistance in the contact points. In this case the relays will act as heat
sink. This is a sign that it is worn. The picture below explains
why. When a relay contact becomes
corrupt, caused by arcing or other means electrons will converge
in poorly conductible space. Replace the relay
if you suspect that it runs too hot. By not doing so, you can run the risk of another
solder joint failure.
Sometimes a fuel pump may run endlessly due to the relay contacts welded
together. Another term for this is resistance welding.
Figure 1.1 This picture
shows how several holes may be drilled on the side of the case to
vent the flow of heat and allow the relay to run cooler.
Many have suggested that holes will not affect the relay after
new, proper solder application. "The problem lies in the bad solder
application (caused by the wave solder process by Mitsuba.) Once the solder joints
have been properly repaired the relay should last the life of the
Also note that your relay
may run warmer indicating that you may end up with the same symptoms.
More holes will not work if your relay is worn.
BACK TO MAIN RELAY HOME