Relay trouble
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Junior User
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Relay trouble
94 Explorer 4x4 Auto 4.0l
What would cause about each and every relay in the power distribution box to systematically go bad over the course of a month? First the blower motor started working only when it wanted to, changed the relay and now it's fine. Then the ABS light came on and wouldn't go off, changed the relay now it works. Tonight the fuel pump didn't make its usual powering-up sound. I started it up a few times, it ran crappy and died. On a hunch, I replaced the relay and it started and ran fine. I know this thing's 11 years old now and all of the relays looked like the originals, but I'm thinking something else must be up. Any ideas??? also, when you remove the old relays they are pretty hot. Not hot enough to burn your hand, but real hot.
What would cause about each and every relay in the power distribution box to systematically go bad over the course of a month? First the blower motor started working only when it wanted to, changed the relay and now it's fine. Then the ABS light came on and wouldn't go off, changed the relay now it works. Tonight the fuel pump didn't make its usual powering-up sound. I started it up a few times, it ran crappy and died. On a hunch, I replaced the relay and it started and ran fine. I know this thing's 11 years old now and all of the relays looked like the originals, but I'm thinking something else must be up. Any ideas??? also, when you remove the old relays they are pretty hot. Not hot enough to burn your hand, but real hot.
Last edited by billsdaddy; Jun 30, 2005 at 05:59 PM. Reason: forgot to add
Elder User
Joined: Jan 2004
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From: Pauline, South Carolina
Age and heat may be the culprit. Did you check the connections where the relay plugs in? If good connection is not made, the resistance can cause heat (and the heat more resistance) and it can burn out the relay. Age and resistance internally at the contact points in the relays can do the same thing. Age, environment, etc. can all have a part. Have they ever been sprayed with acid? (exploding battery) There are a number of possible problems, but other than checking the plug in connections, I don't think I'd worry about it unless the new relays start going out.
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Joined: May 2002
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From: Phoenix
Yeah. I'm wondering if he lives near the coast where salt air helps everything die early. I have a 93. It spent a total of 4 years in the SF bay area, about 2 years in Dallas (not my fault) and the rest of the time here in Pheonix. I have never had to change a single fuse, relay, starter, alternator, fuel pump - nothing electrical except the freaking batteries that don't last for squat in the desert. 168Kmiles.
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Yeah. I'm wondering if he lives near the coast where salt air helps everything die early
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From: Phoenix
I didn't check the schematic but diodes are an electrical component that only lets current travel one direction. They are used in wheastone bridges to change AC into DC current. Yes wheatstone - I'm not making this up. So my impression is that they are part of the charging system. I saw these on mine too but never paid them much attention.
So I don't think it's the heat but the humidity that is your enemy. I live in Phoenix and pure heat of 112 is hotter than pure heat of 95, even though it is "Dry Heat". I have never had an electrical problem. Yet, I've never heard of what you describe either.
So I don't think it's the heat but the humidity that is your enemy. I live in Phoenix and pure heat of 112 is hotter than pure heat of 95, even though it is "Dry Heat". I have never had an electrical problem. Yet, I've never heard of what you describe either.
Elder User
Joined: Jan 2004
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From: Pauline, South Carolina
Remember that those vent holes to let heat out can let more moisture in. If it's getting hot, I'd check those connections. As to the diodes, while a wheatstone bridge (or diode triplet) is used as a recitifier to convert AC current to DC, I suspect the ones you're referring to are there to protect the PCM from reverse polarity issues. The rectifier is internal to the alternator.
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94 Explorer Relays
Had apparent intermittent on the fuel pump relay. Showed up most after five minutes of engine off... just enough time to fill the gas tank, then nothing. Finally traced it to the control module relay which supplies current to the fuel pump relay.
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New User
Joined: Jun 2005
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From: Northern Virginia
Where did you find the control module relay?, when I changed the fuel pump relay on mine there are two other relay's near by but slightly different P/N. Having similar issues with no start on our 95
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Posting Guru
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From: Phoenix
Yeah OK I really didn't believe my story abouy the diodes part of the charging system either. Just the only thing that made any sense without looking at the diagrams. (Sorry. It was late and I was too tired to look it up.) Voltage regulators used to be external, then they all went internal to the alternator. Why go with part of the system then back into a fuse box?
So my diagrams say there is a diode that power runs through from the ignition switch to the PCM relay - control circuit. Once the relay is triped, PCM is powered right off the battery with no other diodes in the schematic. But I have 2 diodes in my fuse box. Not sure if they are hooked up in series for the relay control circuit or if one is for the control circuit and the other goes to the PCM power input. Anyone know the answer to this one?
So my diagrams say there is a diode that power runs through from the ignition switch to the PCM relay - control circuit. Once the relay is triped, PCM is powered right off the battery with no other diodes in the schematic. But I have 2 diodes in my fuse box. Not sure if they are hooked up in series for the relay control circuit or if one is for the control circuit and the other goes to the PCM power input. Anyone know the answer to this one?
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