[65 pile]

Hi I hope someone can be of some help here. I re-wired the dash in my 65 GTO a month or so ago and things seemed to be working fine. Well today I turned on my dash lights and at first the water temp gauge just pegged out and I had no lights in that pod (oil pressure / water temp.). I looked under the dash and wiggled a few wires and the lights came back on, and when they are on the water temp is not pegged out but it is higher than when they are off. Does anyone know what could be causing either of these problems? I left the unused lights without bulbs just hanging around under the dash, is that a problem? All the other pods worked just fine. It just seems to be the few wires in that last pod. It is a brand new M&H dash harness and ralley gauge harness.

Thanks,

Rob

[Andretti]

Originally Posted by 65 pile

...the lights came back on, and when they are on the water temp is not pegged out but it is higher than when they are off

This is normal. Heat from the headlamp mixes with air being drawn through the radiator. This increases coolant temperature.

This is why I try not to use my high beams too often.

[Ben M.]

Originally Posted by Andretti

This is normal. Heat from the headlamp mixes with air being drawn through the radiator. This increases coolant temperature.

Never heard this before.

When you turn the lights on does the gauge go up instantly or over time? If instantly, it sounds like a grounding issue (just because the harness is new does not mean the engine and harness are all grounded nicely together to the chassis). If over time, how much and how long does it take?

My 1980 Trans Am had this issue due to poor grounds - good grounding fixed it. My 1978 Bonneville goes up ever so slightly instantly when the lights come on, I haven't bothered to take the dash apart to fix the grounding there though.

[performerrpm]

Originally Posted by Andretti

This is normal. Heat from the headlamp mixes with air being drawn through the radiator. This increases coolant temperature.

This is why I try not to use my high beams too often.

[guccieng]

i hope he's only kidding...

[Old Goat 67]

Well yeah.

But it sure sounds feasible...........

[65 pile]

Originally Posted by Andretti

This is normal. Heat from the headlamp mixes with air being drawn through the radiator. This increases coolant temperature.

This is why I try not to use my high beams too often.

Thanks for the response. I'm pretty sure this is not the problem because I was only turning on the dash/parking lights and not the headlights.

Originally Posted by Ben M.

Never heard this before.

When you turn the lights on does the gauge go up instantly or over time? If instantly, it sounds like a grounding issue (just because the harness is new does not mean the engine and harness are all grounded nicely together to the chassis). If over time, how much and how long does it take?

My 1980 Trans Am had this issue due to poor grounds - good grounding fixed it. My 1978 Bonneville goes up ever so slightly instantly when the lights come on, I haven't bothered to take the dash apart to fix the grounding there though.

Ben - thanks for the response. It does go up instantly. Maybe it is a grounding issue. I know the dash is grounded pretty well, but is there somewhere I should be looking to check and make sure I have a good ground? It certainly sounds like a grounding issue, I just don't know where to look.

Thanks again.

Rob

[Old Goat 67]

Here's an idea, just run a temp wire from the neg term on the battery and under the dash to the back of the gauge as a test to see if it "fixes" the problem.

If it does, then go hunt your ground "issue" with a VOM.

[65 pile]

Originally Posted by Old Goat 67

Here's an idea, just run a temp wire from the neg term on the battery and under the dash to the back of the gauge as a test to see if it "fixes" the problem.

If it does, then go hunt your ground "issue" with a VOM.

Thanks I will try this. Being a novice at troubleshooting electrical problems I have to ask the dumb question. How do I trouble shoot a ground issue with a VOM?

Also I don't know if this makes a difference or not but the oil pressure gauge was also acting weird when all of this stuff was happening. I don't think it is just involving the water temp gauge, I just mentioned that one because it did give a different reading when the dash lights were turned on. Let me re-phrase all of this. At first when the lights did not work in that pod, both oil pressure and water temp would peg out when the dash lights were turned on. Once I wiggled the wires and the lights in that pod started working again the oil pressure gauge seemed to work fine, but the water temp gauge would give two different readings depending on if the dash lights were on or off. About maybe 20* or so higher with the dash lights on (never the headlights). I still don't know if I have made this clear or not. It's hard because I know what is happening and I think that I am explaining it where others understand what exactly is happening, but in the past I have thought that and I just don't explain stuff clearly. If anyone needs me to explain something differently please let me know.

Thanks,

Rob

[Old Goat 67]

Use that same ground lead from the battery as a reference to ground and read the ohms from it to the housing of the gauges etc. Should be 0 ohms, anything higher than 1 or 2 ohms would indicate a place you should look.

In essence, the ohm reading from your dash panel should be 0 ohms to that lead from the battery, because it should be all metal to metal from the body back to the battery neg post through the ground straps on the firewall. Get the concept?

Don't worry about asking dumb questions, that's how you learn. Therefore, no question is really dumb.

Charles

[Old Goat 67]

Pretty sure were on the right track.

PM sent with my phone number if you need it.

Charles

[65 pile]

Charles,

Thanks I've got your number handy. I will call it if I need to. I think I found the problem in that there are no ground straps on the firewall. I would assume this should be causing me major problems. Would this however affect the dash wiring and lighting?

Thanks for all your help.

Rob

[Old Goat 67]

YES

[Andretti]

............

[65 pile]

Charles thanks for your help on this one. I will be ordering a set of ground straps on Monday and when I get them all hooked up I will let you know what happens.

Again thanks to everyone for all the help. This forum is amazing.

Rob

[Old Goat 67]

Cool man, be sure and let us know. Hey, you could make a couple of ground straps out of wire and term lugs to test this theory.

[Peter Serio]

You have no ground at the 4th pod, this will cause your dash lights to not work & also gauges to "peg." Pegging an old, worn out, 45 year old gauge can cause the shaft to twist in the magnet, that &/or the shaft to rotate inside of the pointer stem; either of these two events will throw the gauge off calibration for good. When this happens the gauge's internal coil needs to be replaced. When the gauges are manufactured new, and before the capsule is sealed the factory (AC delco) placed one and 1/2 drops of a special silicone buffering fluid in-behind the magnet disc. This helped to give a nice smooth "even" movement to the pointer indication. Over time with cold, heat & use this fluid will leech into the nylon & then evaporate. It typically takes about 35 to 40 years for this to occur (way beyond the normal life span of any car.)

When this happens it's only a matter of time before the gauge then fails completely. Ramming the pointers past their normal viewable range (such as loosing the ground will cause) even for only a moment can case failure to occur when the gauges have lost all of their original silicone buffering fluid.

Pete

[65 pile]

Pete, thanks for the knowledge. I went out tonight and placed a ground wire like I have seen in a few of your other posts. As of right now the temp gauge rests at it's bottom at the 100* mark (or what ever is the bottom reading I can't see because the pointer is in the way). If this is not correct will someone please let me know so that I know if the Temp. gauge has indeed become faulty.

I will report back once I have the ground straps in place later next week and let everyone know how this turned out. I really appreciate everything everyone posts on here.

Thanks again.

Rob

[65 pile]

I finally have the ground straps on the engine block to the firewall. And to see if just those would be fine I removed the ground wire that I had added to the 4th pod. Just the ground straps alone still made the Oil and Water gauges go wild when the lights were turned on. So I replaced the ground wire to the 4th pod and works fine with the lights on or off. To summarize 4th pod needs a ground wire run to it just as I have seen from some of Pete Serio's other posts , and probably the ground straps help too.

I still think the water gauge is not reading correct. I might try one of those letcric limited sending units. If anyone thinks this is the wrong direction to head please speak up.