I have a 1967 Mustang that is a base model, no a/c, manual windows..... My cluster was halfway working for a few years now. The oil pressure did not work, the amp meter was not working, the coolant temp guage was halfway working and the gas guage worked perfect. I fixed a vacuum leak behind the intake manifold, car started running better and for some reason all of my guages started working, then they all pegged out. All guages except the amp meter are pegged out.

I know that there are no vacuum lines going to the guages, so this is where I was stumped. I am thinking I hit a ground somewhere when I fixed the hose. I was also thinking the voltage regulator may have gone out. Any other help on where to look or what to test would help alot. I am a tech at a VW dealership so I do have decent car knowledge. Thanks

 

The AMP is a passive indicator wired in parallell, if you want that to work you'll need to clean all the connectors. The rest are powered by a Constant Voltage Regulator on the back of the cluster. Sounds like yours is trashed.

 

I completely re-wired my 68 a year ago, which of course is most similar to a 67, so I imagine we have similar wiring. To state up front, I am not a mechanic or expert, but I have done a ton of work on my car (like rewiring it) and I honestly cannot see how a vacuum leak could be the cause of an electrical problem as your electrical gauges are not connected to any device that could be affected by a vacuum leak. The only vacuum dependent devices with wires would be an electrical choke on a carb (three vacuum hoses coming from a carb) and the vacuum advance which would be connected to the distributor - but neither of those has anything to do with gauges unless maybe an RPM gauge if the vacuum advance tubing had a leak.

I have the original shop manual for 65-71 Mustangs, Cougars, etc., and under gauge troubleshooting, there is no mention of vacuum leaks being the culprit.

When I rewired my gauges, I believe only two or three gauges required a voltage regulator so it may not be that if all of them are not working.

The only thing I can thing of, which may be totally wrong, is that the vacuum leak significantly reduced the power of your engine, which could have caused erratic or no readings on your gauges since they require electrical power - all of your alts power may have been going to the ignition coil. Your alternator may not have been providing enough power or maybe its burned out.

I would check the alternator to make sure it is working, if you have an external alt regulator I'd prob replace it cause they are so cheap, and perhaps you may want to replace the gauge voltage regulator.

If your car is still running ok but the gauges arent, I think perhaps when you fixed the vacuum leak, coincidentally the gauges worked for a while. It would seem that now there is no connection between the two issues.

Also check your fuse box - make sure you havent blown any fuses.

The best thing to do, if you have enough money, is get rid of electrical gauges. They can be inaccurate, and if your electrical system fails or a wire is damaged, you wont get a good reading (or any reading). Mechanical gauges I believe are actually cheaper and easy to install. You could get mechanical oil pressure gauge, water/coolant temp, and speedometer. You would have to keep an electric amp, RPM and gas gauge.

Maybe someone else with more experience working on classic cars would have heard of your issue before and how to fix it, but I dont what else to tell you.

Good luck!

 

The fact they all went full means they all see a low resistance or higher voltage which unbalances the gauge's internal coils. It's pretty unlikely that all of the gauges (fuel, oil, temp) see an low resistance at the exact same time on their outputs so the most reasonable causes are the IVR is failed to system voltage or the ground wire to the inst cluster is loose/fell off. Check that the jumper from the firewall to the engine block is good and make sure the ground wire to the inst cluster is also good and tight.

 

Cool, thanks everyone. I was thinking it had alot to do with the voltage regulator or maybe i hit a ground wire when i was repairing the hose. I will check those things and update later. I guess i mostly needed to know how the guages worked, now I know. Thanks

 

Ok, I finally got around to replacing the voltage regulator on the cluster. My fuel guage fluctuates or just sits at empty now. I filled the tank this morning. The coolant and oil pressure guages are acting like they are getting no voltage now. I think the external regulator in the engine bay is what I am going to replace next.

I tested the alternator at the battery and was reading 15.5v which is pretty high, but I'm assuming the regulator is bad. I'm not 100% sure on how that setup works. Any info would be appreciated. I noticed the voltage will start at 14.3v and then jump real fast to 15.5v. The voltage will also drop to 12.4v when the regulator is unplugged.

 

Installed the voltage regulator and fixed an idle issue instead of the cluster, lol. I think I have a wiring problem behind the dash. I'm going to take it apart and see what I can find.

 

your alt voltage regulator is within specs according to the service manual.

check the ground to your gauges and see if it's good.