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How to solder and fix the Main Relay.
[Click to enlarge] Introduction: The main relay failure is originally caused by the poor solder application from the factory. As a consequence, raise areas on the joint indicate a "dry" joint which can lead to an open circuit. This is caused by dirt in the joint area and has resulted in an unacceptably high resistance. When the terminals expand, contract and vibrate, it is likely that a layer of hard oxide has built up inside the joint. The layers are to be removed.
For this repair project you will need a:
main relayor [90-93 Acura Legend Main relay] or Acura Honda Main relay
Bare-bone main relay, Where can I find the MainRelay?
a 15-30 watt soldering iron
a Rosin core solder
a solder wick or
a De-soldering pump
Start by carefully prying the main relay:
Clip----->main relay Stick a flat small flat screw driver in between.
Separation Steps: What to look for:
Picture of separation procedure Picture of where to solder
Fig. 12 click to enlarge
1. Stick a small flat head screw driver in between the wall flap (a clip) and the relay base.
2. Do not go in too deep. Pry it open just slightly.
3. While holding it still, use the same screw driver, pry the other side.
4. While holding it still (and cleared of the locking edge) pull the relay straight out, or forward.
5. Installation is reverse of the procedure (Note: The main relay will only go in one way into the housing.)
Warning: Do not stick the screw driver too deep inside. You may damage the relay's mechanical or electrical parts.
How to solder correctly
The image above shows several good and bad examples. More soldering examples (external link.)
*TIP:
CAUTION:
Try not to heat the joint too long, because the copper traces on the circuit board may lift.
Health warning:
Do not over expose your lungs or eyes to the fumes. Wash hands with soap and water after touching the PCB's and leads.
Quick Step 1: Desolder the faulty relay terminals (shown on fig 12 above.).
Desolder using pump [Heat the solder, position pump verticle to the terminal. Remove the solder gun and suck the melted solder.] Or desolder using a wick [Heat the solder, press the wick down on the soder with the gun then snip out the used wick and repeat.]
Step 2: Heat the terminal and the copper trace with the soldering tip while applying rosin core solder to terminal. [Heat the terminal then apply solder. Position the relay on its side to stop solder from running out the bottom.]
2 Picture of where to solder
[This picture is illustrated for non-English readers.]
If you do have a joint which looks in need of rework don't be tempted to just reapply the iron. This is unlikely to succeed as the solder in place will have no flux in it, so the flow across the joint will be worse than when it was first made. Better to remove the solder, using a desoldering pump or copper braid, and make the joint again. The flux's job is to strip away all of the grease from the surfaces to be soldered, thus ensuring that the solder will flow properly. A concave should be formed with an angle of 40 and 70° from the horizontal. †
Click here if you still have trouble creating a perfect joint.
Step 3: Clean with steel wool, inspect for imperfections then coat with lacquer (or clear nail polish) to prevent oxidation.
Step 4: Install onto the vehicle in a lower, practical location, easily accessible in the future. Your work is done.
4 See all locations >>
Further explanations:
When the relay coil cannot dissipate heat, the solder on the joint weakens, a "dry" joint is formed resulting in an unacceptably high resistance. The joint begins to heat up and weakens then develop into a dry joint, leading to an open circuit once the motor is shut off. Once cooled the terminal contracts downward and complete the circuit. The dry solder joints could have been easily eliminated if the solder quality is consistent, a concave should be formed with an angle of 40 and 70° from the horizontal and shiny. Four terminals and maybe more on the main relay are known behave this way.
Should I remove the old solder?
Yes. The old solder is of poor quality and damaged. Black areas on the joint indicate a "dry" joint. This is caused by dirt in the joint area and will result in an unacceptably high resistance.
What happens if I just reheat or add additional solder to the joints?
The joint area will result in an unacceptably high resistance. Your symptom may return much earlier than a brand new main relay. The car may stall in traffic and won't start.
Current flows from left to right
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 the contact is worn. The picture above explains why. When a relay contact becomes corrupt, caused by arcing or other means electrons will converge in poorly conductible space heating up the relay further and could result with no power to the relay, thus no power to the fuel pump. 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. Note: The new relay will most likely use the same poor quality solder/application. Its practical lifespan is 8-10 years.
Sometimes a fuel pump may run endlessly because the relay contacts have welded together. Another term for this is resistance welding.
Overview
Solution
FAQs
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Technical Details
Troubleshoot
Soldering Relay
TROUBLESHOOTING
See FAQ for basic troubleshooting. Relay must have these wires and number stamped on the terminals to be considered a main relay suitable for this diagnose. If so, measure them to see if they are as specified below. CAUTION: We recommend that you run a fuse (5-20A) in series to the battery for the bench test.
For most Accords:
Main Relay bench test: Accord 90-94
Step 1: Attach the battery positive terminal to the No.4 terminal and the battery negative to the No.8 terminal of the main relay. Then check for continuity between the No.5 terminal and No.7 terminal of the main relay.
* If there is continuity, go to step 2.
* If there is no continuity, solder the relay terminal and retest.
Step 2: Attach the battery positive terminal to the No.5 terminal and the battery negative to the No.2 terminal of the main relay. Then check for continuity between the No.1 terminal and No.3 terminal of the main relay.
* If there is continuity, go to step 3.
* If there is no continuity, solder the relay terminal and retest.
Step 3: Attach the battery positive terminal to the No.3 terminal and the battery negative to the No.8 terminal of the main relay. Then check for continuity between the No.5 terminal and No.7 terminal of the main relay.
* If there is continuity, the relay is OK. If the fuel pump still does not work, check the harness and/or fuel pump.
* If there is no continuity, solder the relay terminal and retest.
Schematic diagram
Main Relay in circuit test:
Terminals: For most Accords: While still connected to the vehicle check that:
1. Yel/blue should have +12 volts battery, always.
2. Blk should be grounded always. Connect your negative voltmeter or DMM lead here.
3. Blk/yel should have +12 volts with ignition ON.
4. Not used.
5. Yel/blk should be +12 volts with ignition ON.
6. Blu/Red (auto only) Blk/grn (manual only) should be +12 volts at START.
7. Yellow should have +12 volts temporary with ignition ON, if idling or start Yellow should have +12 volts.
8. Grn/blk should ground temporary with ignition ON or idling, if idling or start Grn/blk should ground.
If all readings are okay except on either terminal 3) ECU-Injector or terminal 7) Pump then the relay should be soldered..
Main Relay bench test: Acura Legend 91-93
Step 1: Attach the battery positive terminal to the No.4 terminal and the battery negative to the No.8 terminal of the main relay. Then check for continuity between the No.5 terminal and No.7 terminal of the main relay.
* If there is continuity, go to step 2.
* If there is no continuity, solder the relay terminal and retest.
Step 2: Attach the battery positive terminal to the No.6 terminal and the battery negative to the No.2 terminal of the main relay. Then check for continuity between the No.1 terminal and No.3 terminal of the main relay.
* If there is continuity, go to step 3.
* If there is no continuity, solder the relay terminal and retest.
Step 3: Attach the battery positive terminal to the No.3 terminal and the battery negative to the No.8 terminal of the main relay. Then check for continuity between the No.5 terminal and No.7 terminal of the main relay.
* If there is continuity, the relay is OK. If the fuel pump still does not work, check the harness and/or fuel pump.
* If there is no continuity, solder the relay terminal and retest.
Factory unabridged Legend first generation main relay and fuel pump test and how to install fuel pump. [PDF printable version 240K] cache
Factory unabridged 95-97 Civic main relay test [PDF printable version 240K] no cache
The images below show the homemade holes and the factory made holes. The image on the far right (which has factory holes) is a fuel pump relay known to be reliable. Holes will not affect the solder joints once the solder joints are properly soldered.
Read more regarding this topic: Holes on relay case.
More relay diagram ( Mitsuba rz-0088, rz-0063 and etc.)
<< Back to main relay information page.
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