Check the additional leads on the positive battery terminal - the 10mm nuts. Based on what you described, you have a low-voltage issue that goes beyond any ground point. i imagine this suddenly started, and some voltage readings at the battery terminals would help diagnose - after start up and in failure mode.

 

The battery tested fine when the car is running. I've still got to do the main ground on the bell housing. It's cold and raining here so I'll wait until tomorrow to get under the hood. Good call on the positive leads at the cable, they seem to get a lot of weather in that location. I'll do all the grounds again and use some dielectric grease. I'll pull the brake switch tonight and see if I can do anything with it. Thanks everyone for all your help with this. I'm very grateful.

 

Curious... what was the voltage of the battery test when the car was running?

 

Looks like one of the ignition relay connections in the fuse box was the culprit. I found out by sheer chance. I was getting hacked off with trying to diagnose the problem, so with the car running I just started jiggling around the ignition relays. Viola! On an interesting note, cleaning all the grounds has made a big difference to the whole electrical system, my headlights are way brighter, the alternator sits bang on 14V. Even my interior light is brighter! I was surprised how nasty the positive battery connections actually were. They looked fine but when I pulled them apart they obviously needed a good clean. One of the grounds on the passenger side front frame rail was also a bit loose and corroded. Thanks to all! I appreciate the help. There are some very intelligent folks lurking here on Rennlist.

Now I'm back to the dreaded airbag light. The saga continues.

 

hey photodan. i seem to be having the exact same problem as you, and i cant for the life of me figure it out!
my gauges work for like a second when the car is driving and then shut off.. and my brake and reverse lights dont work at all. are they all connected?
what relay should i look at, or clean or replace.
someone help me please this is a nightmare!!!

 

check the ignition relay mine went bad, and all sorts of weirdness happend, brake lights gauge lights sunroof all were sparatic at best