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RX-7 1st Gen Specific (1979-85) RX-7 1979-85 Discussion including performance modifications and technical support sections

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Old 07-26-2016, 10:30 AM   #1
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Default SA Electrical Help

I just picked up a clean SA ('79) sight-unseen. I had a dealership local to the seller check it out and they found no issues. However, it has some electrical issues I wasn't expecting as neither the dealership nor the previous owner mentioned them:

1. The tachometer doesn't work. I verified with a timing light all four plugs are getting spark and the resistance across the posts on both igniters is within spec. The gauge isn't getting the engine speed signal and is always displaying the voltage.

2. The "add oil" light is on but the oil level is at the "full" mark on the dipstick. I haven't checked the oil level sensor yet.

3. The "add coolant" light is on but both the radiator and overflow bottle are full. I haven't checked the coolant level sensor yet, but grounding the connector to the negative terminal of the battery doesn't make the light turn off.

4. The "gen" light is on. Voltage at the battery and alternator "B" terminal checks out around 12.25V with the car off. With the ignition on and the car running the voltage is 11.75V at the battery and 11.50V at the alternator. According to the dash voltmeter increasing engine speed increases voltage, although it does show voltage going well past 14V so I don't know how accurate that is. I can't find a 1979 service manual to check the alternator as it appears to be different from the 1980.

I don't think the dealership and seller are lying when they said nothing was wrong when they last had the car. I'm thinking there's something wrong with the charging system that's linked to everything as it seems unlikely all these sensors would fail at once. I can't think of anything that could have failed during the delivery of the car. Am I missing something?






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Old 07-26-2016, 11:42 AM   #2
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1. The tach gets it signal from the leading ignitor. If the lead isn't hooked up that would explain it. Pull the elect. diagrams to verify the lead thats required.

1 & 2 & 3 & 4 May be related to the solenoid over by the clutch master. It controls the idiot lights
and may be not turning them off? Something to check.

4. You should be seeing over 12 volts when idling and up to 14 volts at higher rpms. The 79 has an external regulator so you may need to look into it to make sure its working correctly. Its also over on the fender by the clutch master.

All this aside, it was delivered via a truck? Maybe some connections vibrated loose. I'd
look around in the bay for any dangling connections.

You could post up some pics and maybe get some help by crowd sourcing on here.
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Old 07-26-2016, 12:34 PM   #3
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Quote:
Originally Posted by t_g_farrell View Post
1. The tach gets it signal from the leading ignitor. If the lead isn't hooked up that would explain it. Pull the elect. diagrams to verify the lead thats required.

1 & 2 & 3 & 4 May be related to the solenoid over by the clutch master. It controls the idiot lights
and may be not turning them off? Something to check.

4. You should be seeing over 12 volts when idling and up to 14 volts at higher rpms. The 79 has an external regulator so you may need to look into it to make sure its working correctly. Its also over on the fender by the clutch master.

All this aside, it was delivered via a truck? Maybe some connections vibrated loose. I'd
look around in the bay for any dangling connections.

You could post up some pics and maybe get some help by crowd sourcing on here.
I'll take some pictures later today. I verified the tach signal is from the lead igniter (Y/G wire) and it is plugged in. The fact that I'm seeing less than 12V with the car running at the battery and alternator makes me think something's up. Perhaps something in regulator got shaken loose since it was delivered by truck. There are a couple disconnected connectors over by the clutch master and I was able to identify and reconnect one: the brake fluid level sensor. I'm not familiar with the solenoid you mentioned. If it controls the idiot lights it could be the culprit since all the lights in question usually get switched off after the car is started. Right now the only ones that go off are the "brake" and "seatbelt" lights.
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Old 07-26-2016, 12:47 PM   #4
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Shameless thread bomb of the Manuals....

http://foxed.ca/index.php?page=rx7manual#firstgen


*smoke bomb*
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Old 07-26-2016, 01:48 PM   #5
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Quote:
Originally Posted by chibikougan View Post
Shameless thread bomb of the Manuals....

http://foxed.ca/index.php?page=rx7manual#firstgen


*smoke bomb*
Been digging through those quite a bit lately. Unfortunately it doesn't have a 1979 FSM and there are significant differences between 1979 and 1980 when it comes to the charging and ignition systems. Hell, my wiring harness differs from the 1979 one on that site. Maybe it's because I have an early build (March 1978)?

I took some pictures of the area by the clutch master cylinder. I have four connectors that aren't connected:



From the insulating muck on them it appears they have never been connected. Only two would make a matching pair anyway. Other than that I verified the alternator regular was fully connected and nothing looked out of place or broken. Since I'm reading less than 12V at the battery and alternator I'm thinking the regulator and/or alternator are somehow bad. If anyone knows how to check their function on a '79 let me know.
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Old 07-26-2016, 04:51 PM   #6
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So I've identified the four unplugged connectors. Apparently all these cars had the same harness whether they were MT or AT and Federal or CA emissions. All the unplugged connectors have something to do AT and CA emissions so they are rightfully disconnected in this car.

I can't seem to find anything loose, broken, or disconnected that's vital. I'm confused by one particular relay, however, that doesn't show up in any of the parts lists. Does anyone recognize this:



The blue and yellow wires travel up along the firewall and into the cabin on the passenger's side:



Because of this I assumed it has something to do with the optional A/C on the car. However, the A/C relay is already accounted for, although the relay has "Window Relay" stamped into its side.

Looks like an alternator and/or external regulator problem is still the top hypothesis.
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Old 07-26-2016, 05:40 PM   #7
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Hmm, that relay wiring does not look at all OEM - if it came with the car, I would expect some sort of plastic connector for all pins, not spade lugs on each terminal & individual wire.

I'd say it's part of some aftermarket accessory that a PO put in or had put in - maybe part of an alarm system, or car audio accessory?
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Old 07-26-2016, 09:30 PM   #8
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Quote:
Originally Posted by Pete_89T2 View Post
Hmm, that relay wiring does not look at all OEM - if it came with the car, I would expect some sort of plastic connector for all pins, not spade lugs on each terminal & individual wire.

I'd say it's part of some aftermarket accessory that a PO put in or had put in - maybe part of an alarm system, or car audio accessory?
I agree, but it definitely controls the A/C. With it disconnected the A/C doesn't work at all. The other "A/C relay" does something with idle control. With it disconnected the idle doesn't bump up to compensate for the extra load on the engine. I almost wonder if this was some kind of aftermarket A/C system installed after the car arrived stateside.

Still no "aha" moment though. I had my wife help me for a few moments and I was able to confirm voltage does increase with engine speed but not nearly as high as indicated on the gauge.

I also figured out why the steering wheel was so sloppy. Some kind of plastic o-ring at the end of the steering column has completely rotted out. Not sure if I'm SOL or if there's some way to replace it.
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Old 07-26-2016, 09:32 PM   #9
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Looks like it may have had some fusible links so they put in a relay.
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Old 07-26-2016, 09:48 PM   #10
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There is a blue and yellow that go into the cab for the:

Ignition

Alt Warning Light

a-10 connector...
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Old 07-26-2016, 09:56 PM   #11
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It looks to be a regulator for the alternator... from the 79 wiring diagram.
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Old 07-26-2016, 10:05 PM   #12
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Yeah Voltage Regulator...

http://www.rx7club.com/1st-generatio...pgrade-967330/
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Old 07-26-2016, 10:58 PM   #13
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Quote:
Originally Posted by chibikougan View Post
There is a blue and yellow that go into the cab for the:

Ignition

Alt Warning Light

a-10 connector...
Yeah, I see it now. The YL (yellow/blue) wire runs from the "L" terminal on the external voltage regulator to the alternator warning light but is also connected to the oil level warning light, coolant level warning light, and tachometer circuits. It's still a question of whether it's the alternator or the voltage regulator and I still don't know how to test them. The only thing I've been able to verify is the is the L terminal doesn't have continuity with the A and S terminals, but does with the others, which is consistent with the wiring diagram. I'm going to dig into the display more tomorrow to see if I can't find a short somewhere.
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Old 07-27-2016, 12:12 AM   #14
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Most parts stores have the ability to bench test alternators, whether or not this test can be done with your application, I don't know but it's worth a shot.

My guess is the regulator but I'm not familiar with the first gens and their parts.
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Old 07-27-2016, 12:19 AM   #15
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As for the gauge. . . Move the yellow signal wire to the Trailing coil and see if there is no change to confirm that you don't have a defective coil. A failed Leading coil is one reason for a dead tach.
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