Electrical Issue

[jimbo01]

Last evening I had the car running in the driveway. The water temp was up to 90 on the gauge which is normal. Then I turned on the headlights on low beam and the water temp gauge went up 10 degrees to 100. I then turned off the lights and the temp went back to normal quickly. What is going on?

[TimeForACobra]

I have the same problem... Was mentioned to me at some point (just don't remember who or when) that it sounds like a grounding issue...

[James Stern]

bad grounds. Either ignore the readings or fix the grounding.

[jimbo01]

After getting your advise regarding grounds. I relocated the battery and changed the ground wire location. I will make sure that ground is good. Could be my problem. Will advise tomorrow.

[vref120]

Mine does the same

[James Stern]

Jimbo,

I had the same issue and took the car to a guy that knows automotive electrics. He fixed up all of the gauges so that they work properly. It took him a couple of hours.

[jimbo01]

Just called Frank at Boca. He said all of these cars do that. I guess its just a built in screw up by Backdraft. I know my hot rod I built and wired does not do that. Wish I knew what your guy did to fix the problem. I am going to install new Smith gauges this winter and the water temp and oil pressure are manual. This will correct that problem. I guess I need to rewire the gauges.

[James Stern]

You might want to look at Speedhut in Utah.

[itstock]

Originally Posted by jimbo01

Just called Frank at Boca. He said all of these cars do that. I guess its just a built in screw up by Backdraft. I know my hot rod I built and wired does not do that. Wish I knew what your guy did to fix the problem. I am going to install new Smith gauges this winter and the water temp and oil pressure are manual. This will correct that problem. I guess I need to rewire the gauges.

My car has never done that. What kind of gauges do you have?

[Xack]

With grounding issues at the gauges, make sure you don't have a long daisy-chain from one connection to another and another. This goes for power as well. You can easily group up to 4 wires into a junction and connect it to ground. etc.
If you don't want to redo your wiring, first see if you can't add points to ground in the daisy-chain or at each end. My dash wiring was one long chain. When you turned on the dash light you could see the lights come on in a wave from left to right. The volts was reading 10 at full battery. I rewired all power and grounds and its a big difference.

[Rick Parker]

Voltage fluctuation when lights turned on. Look at either your voltage or Amp gauge, needle will move.

[jimbo01]

The gauges are VDO and the alt is suppose to be a 100amp. I took the battery box out and made sure the ground there is perfect. I am going to check the chassis ground for proper connection. Will know more tomorrow.

[Ron61]

What does it do if you turn the headlights on high beam? Grounding is always a first suspect in strange things with these cars, but it isn't always the problem. The lights sholdn't affect your temperature readings unless Backdraft has a setup that is quite different from what I have worked on. I used VDO gages in my race Cobra and I wired every gage and light with seperate and back up wiring so if one came loose or broke, everything would still work. Also I did add a lot of extra grounds to everything as I never was a big fan of daisy chaining things together. But as said above, check grounds first.

Ron

[jimbo01]

Ron

What I have been able to determine is that Backdraft uses a single ground wire to all the gauges. What gauge wire I am not sure. This is not according to VDO instructions. VDO says in their instructions to run a 14ga ground wire to each gauge in order to get a correct reading. Discussing this with several other electrical minded techs, this will be my next step.

[Kobura]

My Backdraft has "stock" gauges except for the speedo and tach which are from AccuMeter. Sorry, but the gauges do not behave like yours, so I cannot be of help.

[GLS-BDR226]

I have an early BDR with VDO gauges. i had an issue with the speedometer bouncing from 0-45 while sitting still when the headlights were on. Had to rewire the speedometer. It was installed wrong.

[jimbo01]

Kobura

I am not sure what you mean by "stock" gauges. They normally would be Autometer, VDO, or Smith's. Depending on what Backdraft installed in the build this should be the case. If the speedo and tach are Autometer then most likely the others are the same. It's possible that your gauges do not need the additional ground that the VDO gauges need. Read your gauge instillation instructions for this info. You can find this on line by checking the manufacturers instructions.

[Cashburn]

Originally Posted by jimbo01

Kobura

I am not sure what you mean by "stock" gauges. They normally would be Autometer, VDO, or Smith's. Depending on what Backdraft installed in the build this should be the case. If the speedo and tach are Autometer then most likely the others are the same. It's possible that your gauges do not need the additional ground that the VDO gauges need. Read your gauge instillation instructions for this info. You can find this on line by checking the manufacturers instructions.

There was a year of production that Backdraft installed their own gauges. There were issues so the Speedo and Tach on the cars we delivered received a matching Autometer style gauge in those places. These gauges had LEDs instead of bulbs and might be the reason the grounding was not an issue, since you are reporting the issue is when the lights are on.

[Xack]

Originally Posted by jimbo01

Ron

What I have been able to determine is that Backdraft uses a single ground wire to all the gauges. What gauge wire I am not sure. This is not according to VDO instructions. VDO says in their instructions to run a 14ga ground wire to each gauge in order to get a correct reading. Discussing this with several other electrical minded techs, this will be my next step.

Yep, don't daisy-chain grounds or power. You can still just run a ground wire to the other end of the chain or the last point. That will give the current 2 paths instead of just one to ground. It'll be a quick fix.

[jimbo01]

I do not understand "stock" gauges. Most have VDO, Autometer or Smith's gauges. If you have and Autometer speedo and tach most likely you have Autometer guage package.