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1965 Ford Mustang Malfunction - Electrical & Lighting Systems
Question: Hello:
I recently had a Painless wireing harness (part 201120) installed in my 1965 Mustang Coupe. The car has gauges (vs idiot lights). Things were good for a month or so, they one day when I started the car, all the guages moved fully to the right and stayed there. When I turn the car off, they return to their state of rest on the left. All guages are affected.
I presume this is a ground or short problem, since it is affecting all of them. Also, nothing else on the car is affected. Everything else works fine.
My question is, where should I look first? Is there a ground wire connection on the instrument cluster itself? Does it sound like something came loose, or maybe a short? I don't want to tear out the cluster if there is another, logical place to look first. Thanks for any help you can give me.
Tom Bell Phoenix
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Technican: Tom, Do you have recourse with the wiring harness installer?
When a gauge goes full right upon being powered up it means most often that a wire from the sending unit to the gauge has become grounded. This can be due to routing the wire from the sending unit too close to a bracket edge, a moving part that could wear the wire insulation, or hot parts that cook the wire insulation away and allow metal-to-metal contact between the wire and whatever is close.
I'd be looking closely at the route the harness takes from the engine to the cluster. It can be a very minor nick or wear of the wire insulation that you'll find. Reroute and/or repair the harness as needed.
You could also chat with some of the Mustang Owners Clubs you'll find with a "Google Search" to see if they have different input than I have.
Owner: No, unfortunately the guy who did the wiring is no longer at the shop, and the shop was sold. i just don't want to deal with them any longer. (long story). the key here i think is that L the guages are moving to the right... i contacted painless and here is what they wrote back"
The ground is the common link. Most gauges require a power, ground and sending signal. The sending signal is a variable ground. The full ground on a fuel gauge means empty on most gauges and open means full. Full ground on temp means hot open means cold. Full ground means oil pressure and open means none and so on. It sounds as though the cluster is having a ground issue. One common issue is the lack of a body ground. Make sure you have a strap from the engine to the firewall or the negative side of the battery to the fender. Do not rely on motor, transmission or body mounts to make your grounds. Make sure the ground to the cluster is clean and tight to a known good ground (check it with a voltmeter).
again, since they are all affected, i wonder if I am looking for a common issue... just don't know quite where to start. also, everything else on the car is fine, so it doesn't seem like a basic ground issue... still stumped!
Technican: It sounds like a problem with harness or installation itself.
Have you tried to troubleshoot by following the installation manual?
painlesswiring.com/manuals.asp
Owner: yes, I have the manual, and have done troubleshootin g as much as I can. Short of taking it in and have an electrical guy look at it... that's why I am here. Looking for someone who has worked with Painless kits before and might be able to suggest a couple specific things to check
Technican: I read through the response sent to you by Painless. You released the question on me but I didn't read where you verified the chassis ground to be in place and in good condition. I found the part number of the harness to be 20120.
Is the ground there from battery to chassis and from engine to body? What have members of Mustang car clubs telling you? Part of my response was the suggestion to try and contact them.
Repeated releasing of the question doesn't give a man a chance to follow through and help you find the answer to your question. It doesn't pay much either. (No disrespect intended)
Owner: I believe I hit the release button in error. First time I have used this service.
Battery neg is grounded to the block. The firewall is grounded to the block. Those are the grounds I have found and inspected. They look OK. Again, EVERYTHING else on the car (including the radio which grounds to the dash) is working fine. I have not talked to anyone else in the Mustang Club here. One specific question i had was with this particular model...is there a ground wire connection on the instrument cluster. If so, maybe that is a place to look. Again, I am trying to get info before I tear the thing apart, so I can minimize the operation. The wiring job is relatively new, and no obvious nicks or cuts. But I will keep looking.
Technican: There needs to be a ground from the neg bat post to the body as well. I recommend a 10 gauge wire. If you have one of those washers that looks like gear teeth on the outer edge it goes under the wire connection terminal and will dig into the sheet metal for a good ground. The wire terminal will be forced onto the top of the washer by the attachment bolt.
Thanks for the second chance. I'll work to get a clear answer on the cluster ground.
Owner: Thanks. I will add the additional ground, which it certainly sounds like it needs. Wondering why this system worked for a couple months and then went as it did. That's what makes me think something has some loose or damaged... Again, thanks for the help.
Technican: Grounds are strange. An insufficient ground situation can start out working, heat up and cause resistance that can no longer be overcome until corrected.
Ground is more important to a circuit than power. Without proper ground something won't work. Without proper power something may work but not as designed if at all.
Redundant grounds are seemingly unnecessary until you realize one is missing.
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