Vintage Mustang Forums banner

1 - 13 of 13 Posts

·
Registered
Joined
·
1,004 Posts
Discussion Starter #1
Ok, here's a strange one that so far as got me stumped.
I installed an AAW kit in my car (64.5. vert). Everything is fine with the AAW kit and it all worked perfectly from the first turn of the key.
I also installed Speed Hut gauges. They too are fine and work perfectly.

This weekend I installed the convertible top motor, new hoses and cylinders. The top motor is wired the same way the factory did it and works fine. Top goes up and down with no issue.

But, when I was cycling the top motor up and down it sounded like the gauges were making noise. So, I watched the gauges while operating the top switch and sure enough, the oil pressure gauge was moving with the top switch. The harder the motor for the top was working, the high the oil pressure gauge was reading.

I pulled the inline fuse for the gauges and it stopped.

The top motor is on its own circuit totally separate and apart from the rest of the wiring harness, but somehow there is some electrical noise feeding back through that is causing the oil pressure gauge to move when the top switch is operated. No other gauges move at all and they all share a common 12v power source and ground.

I thought maybe the power top wiring was too close to the gauge cluster so I unscrewed they cluster and let it sit on the column 4-6" away from the top wiring and it still did it.

I called AAW and they are stumped too.
 

·
Registered
Joined
·
888 Posts
Phantoms work in strange ways. I would check all ground connections. Ground loops cause these types of behavior. Check all grounds, all of them.
 

·
Premium Member
Joined
·
4,294 Posts
Is this with engine on or off? The draw on the battery if off or on the alternator or generator when running may be enough that it increases overall resistance and the load on your charging unit and voltage regulator may be a bit much.
 

·
Just some guy
67 coupe, 69 Sportsroof, 86 hatchback
Joined
·
20,616 Posts
Ground problem. My VERY first thought. Voltage drop testing will be your friend. If you've never done any some Youtube people explain it better than I can here.
 

·
Registered
Joined
·
1,004 Posts
Discussion Starter #5
Engine off (that's the only reason I heard the gauge sweep).

I will create a new ground for the pump motor tomorrow and see if that does it.

Although it is still curious why only the oil pressure gauge is affected when all of the gauges share common power and grounds.
 

·
Registered
Joined
·
1,004 Posts
Discussion Starter #6
Ok, forget what I said earlier about other gauges not being affected.

When I was running the car today, the temp gauge was reading way hot, but the laser temp gauge said the car was even up to t-stat opening temp. Popped the cap on the rad and the t-stat was if fact still closed as no coolant was flowing through it.

A little more investigation revealed that when the electric fan kicks on, all the gauges are impacted and that is what caused the temp gauge to read high, so I am getting a lot of electrical noise/feedback from the big amp electrical items that are screwing up the gauges.

Wondering if I should remove the ground for the gauge cluster from the main harness and just ground it directly to the body somewhere?
 

·
Registered
Joined
·
1,870 Posts
Is the ground from your engine to the firewall ok?

Since the block is directly connected to the negative battery cable I wonder if the ground from the body to the block is bad so the electricity is finding a new path to ground through the gauges.
 

·
Registered
Joined
·
1,004 Posts
Discussion Starter #8
Good thought, but the ground from the block to the firewall should be perfect. New engine block, new ground strap, new ground screw and the metal on the firewall was cleaned down to bare metal before attaching the ground strap/screw.

I will double check though.
 

·
Just some guy
67 coupe, 69 Sportsroof, 86 hatchback
Joined
·
20,616 Posts
I believe your gauges are just a symptom, the cause is with wherever you have your fan grounded I suspect first. Secondly the positive side.
I've shown up I don't know how many ground and power connection uses with voltage drop testing that "looked" fine. Just looking and saying you used new parts aren't sufficient. I about got into a fight once with my brother in law over this. Sister's car wouldn't start reliably. He shot the parts cannon at it befor ehe called me. I did some testing and said he needed a new positive battery cable. He refused to believe it as it looked fine and he had thoroughly cleaned both ends. Tried to argue me down. I left. Next day he finally gave up and put a new cable on. Fixed it. Called me later to apologize as he had sliced the cable open and what used to be copper inside was a crumbling green mess. I agreed with him that it was amazing how good the bad cable had looked.
 

·
Registered
Joined
·
1,004 Posts
Discussion Starter #10
I can double check the fan ground too, but if it were the fan ground, that wouldn't explain the first symptom I noticed, which was the oil pressure gauge moving when the top motor was activated- that happened with the engine off and the fan not running.

I'm not saying that a ground can't be the issue, but since the two things that aren't attached to the main harness (fan and top motor) are causing problems, I would think that if there is a problem with a ground that it's either a problem with the one of the main engine/chassis grounds or the gauge cluster ground.

I'll remove, clean and inspect all grounds to be sure.

I'm going to give Speedhut a call in the morning too.


I believe your gauges are just a symptom, the cause is with wherever you have your fan grounded I suspect first. Secondly the positive side.
I've shown up I don't know how many ground and power connection uses with voltage drop testing that "looked" fine. Just looking and saying you used new parts aren't sufficient. I about got into a fight once with my brother in law over this. Sister's car wouldn't start reliably. He shot the parts cannon at it befor ehe called me. I did some testing and said he needed a new positive battery cable. He refused to believe it as it looked fine and he had thoroughly cleaned both ends. Tried to argue me down. I left. Next day he finally gave up and put a new cable on. Fixed it. Called me later to apologize as he had sliced the cable open and what used to be copper inside was a crumbling green mess. I agreed with him that it was amazing how good the bad cable had looked.
 

·
Registered
Joined
·
1,004 Posts
Discussion Starter #11
It's fixed. Good call Magnus. You and Gypsy were correct, it was a ground. I don't know if I didn't tighten it all the way when I installed it or if it loosened up somehow, but the ground screw at the firewall was loose. I cleaned it up, reinstalled it, tightened it up, worked the top switch and the fan and the gauges didn't move at all.
Thanks for your help!
 

·
Registered
Joined
·
377 Posts
In addition to the ground at the firewall, I also ran a ground from where the battery neg cable attaches to the frame rail. Also put some dialectric grease on those connections to keep them clean.
 
1 - 13 of 13 Posts
Top