Instrument gauge de-bugging help needed

386 Views 10 Replies 5 Participants Last post by rrh24, 1 d ago

rrh24

Discussion Starter · 11 d ago

Starting de-bugging process on car. It appears the oil and temp gauges are working. However, yesterday on a test drive about 10 minutes into it I noticed that both the oil pressure and temp gauges went to zero simultaneously along with the aftermarket autosound radio cutting out. About 1 minute later, all 3 came back on at the same time. (It happened 1 other time during the drive).

As a point of reference neither the fuel gauge or alternator gauge are functioning in the cluster. The fuel gauge is pegged at E (I replaced sending unit w/ new tank and checked resistance changes in sending unit before I installed so I'm confident that is not the issue - I did not check check sending unit harness yet). For the alternator gauge it is dead center and doesn't move (I turned on lights w/o key for a few minutes and it didn't move towards discharge).

For the issue of the gauge and radio cutout, does anyone have any insight on what may be causing this particular issue? (there is a new voltage regulator and alternator installed btw).

thx

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myfirstcar66

· #2 · 11 d ago

The ground from the instrument cluster etc is intermittently loose, or power to the instrument and radio circuits at the fuse box are either loose or corroded, is my guess.
The ammeter gauges are famous for not working or barely moving and are often burned on inside, and require ALL grounds to be clean.
Your fuel gauge not working before is a problem with current to the gauge, or between it and the sending unit and its necessary ground, or just a crap sending unit, but it won't work reliably until you fix problem one.

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Woodchuck

· #3 · 11 d ago

I've highlighted the feed path to the IVR in RED in the image below, to where it splices into the ignition "ACCY" circuit. If other functions such as wipers, turn signals, etc., work then it eliminates the ignition switch as a possibility. My guess is that the radio is tapped into the BLK/GRN wire somewhere along this path. Either the radio is causing a short that's killing the feed to the IVR or, more likely, there is a poor connection at the firewall plug(s). It's also possible that if someone used a "Scotch Lok" to attach the radio power they cut the conductor in the BLK/GRN to where the connection WAS intermittent and now it's arced to the point where the connection is lost.

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CJM68GT390

· #4 · 11 d ago

Agree with @Woodchuck, you have an intermittent connection somewhere between in the power supplied (the ignition switch) and those devices. His schematic doesn't show the OE radio wiring. The standard harness has a connection for the radio, and whoever installed your after-market radio may have used it. You might want to get a Ford Electrical Assembly Manual.

The easiest way to diagnose the fuel gauge is to disconnect the wire at the fuel tank sender and ground it against the body. If the gauges goes to F you have a bad sender. If the gauge doesn't move then it's either a break in the wire or the gauge is bad.

For the AMP gauge, you might consider having it converted to a voltmeter.

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rrh24

Discussion Starter · #5 · 10 d ago

Woodchuck said:
I've highlighted the feed path to the IVR in RED in the image below, to where it splices into the ignition "ACCY" circuit. If other functions such as wipers, turn signals, etc., work then it eliminates the ignition switch as a possibility. My guess is that the radio is tapped into the BLK/GRN wire somewhere along this path. Either the radio is causing a short that's killing the feed to the IVR or, more likely, there is a poor connection at the firewall plug(s). It's also possible that if someone used a "Scotch Lok" to attach the radio power they cut the conductor in the BLK/GRN to where the connection WAS intermittent and now it's arced to the point where the connection is lost.
View attachment 897118

thx . Another piece of info - when I installed the radio I tapped directly into block w/ fuse clips (the 20 amp fuse for constant power and the 14 amp accy).

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Woodchuck

· #6 · 10 d ago

rrh24 said:
thx . Another piece of info - when I installed the radio I tapped directly into block w/ fuse clips (the 20 amp fuse for constant power and the 14 amp accy).

Did you tap into the "line" or "load" side of the fuses? LOL.

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rrh24

Discussion Starter · #7 · 10 d ago

I removed the fuses and checked which side was protected and tapped into that side (load). Hopefully that was correct?

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Grabber70Mach

· #8 · 10 d ago

If the radio wire has a inline fuse I would tap into the line side of the fuse you are tapping into.

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rrh24

Discussion Starter · #9 · 1 d ago

Update on electrical issue - I went back and started by re-checking my grounds (battery to block/block to firewall/instrument cluster to dash/ fan motor to dash). I am confident that the grounds are good.
I ran the car and waited for when the gauges (IVR) to cut out again and when they did I found that the the wipers, radio, and fan motor also cut out at the same time. I also checked that I still had continuity across the fuses when everything cut out.

Is it a reasonable conclusion from this info that the issue is related to the ignition switch?

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Woodchuck

· #10 · 1 d ago

rrh24 said:
Update on electrical issue - I went back and started by re-checking my grounds (battery to block/block to firewall/instrument cluster to dash/ fan motor to dash). I am confident that the grounds are good.
I ran the car and waited for when the gauges (IVR) to cut out again and when they did I found that the the wipers, radio, and fan motor also cut out at the same time. I also checked that I still had continuity across the fuses when everything cut out.

Is it a reasonable conclusion from this info that the issue is related to the ignition switch?

That's a reasonable assumption.

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rrh24

Discussion Starter · #11 · 1 d ago

that was it.....put a new ignition switch in it and it is now working.

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