Topic: 69 Mach 1 Electrical Problem

[must69]

I have a 69 Mach 1 351 that I have owned for about 37 years.  It is pretty much original and has not been butchered at any time by any "kid" including me! When I turn on the parking or head lights both turn signal indicator lights in the dash also illuminate.  The turn signals themselves function properly.  My past auto training and experience would tell me that if one were lit that there would be a bad ground with one of the parking lamps on the corresponding side of the car, and upon inspection I would find that side parking lamp socket to be rusty and in need of repair.  Not the case with these. All parking lamps appear to be in excellent condition.  The car is garage kept, and only has 69,000 miles on it.  The printed circuit board behind the cluster is "new" about 10 years ago.  The car has been driven less than 500 miles since then, so that is new.  The only electrical modifications I have made to the car the first being when it was built for drag racing was to relocate the battery to the trunk.  Battery cables are made from heavy multi strand welding cable.  I have replaced the stock alternator with a single wire 90 amp alternator.  Any ideas where to look?  I am at that frustration point.
Thanks.
Phil

[jwc66k]

Phil,
 Almost everybody I know with a 69 or 70 Mustang that had a dash related problem (lights, gages) resolved their problem by "tinkering" with the ground wire at the instrument cluster circuit board. A more drastic fix was to add another ground from the circuit board to the chassis. That method, adding a temporary ground, might be the troubleshooting tool you should try.
Jim

[midlife]

Phil,
 Almost everybody I know with a 69 or 70 Mustang that had a dash related problem (lights, gages) resolved their problem by "tinkering" with the ground wire at the instrument cluster circuit board. A more drastic fix was to add another ground from the circuit board to the chassis. That method, adding a temporary ground, might be the troubleshooting tool you should try.
Jim

I'm not sure this is relevant to the original poster's problems, but I've lately had a lot of customers having problems with 69/70's with dash clusters not working right, despite the wiring going into the dash cluster being perfectly fine.  I don't know if the repro circuit boards are of marginal quality or something else going on.  My personal opinion is that these cards have poor reliability/quality relative to a directly wired dash cluster.

[cobrajetchris]

I have had that same problem before. I pulled out my hazard switch on the column and pushed it back in and I have not had the problem since. I am not sure if the switch was partially out or if I may have a problem down the road with the turn signal switch sticking or a flasher issue. If you have not done that it only takes a second. I agree with the previous post on gauge cluster problems as I have had many and even after having the gauges rebuilt I still have them register wrong at times. I think it's just the nature of the beast.

[must69]

I caught a bit of luck for once while trouble shooting this.  I was feeling around the back of the cluster and the turn signal indicators flashed off and on.  I actually could narrow it down to a specific area of the PC board.  I pulled the Instrument cluster out and found a corner of the Printed circuit was actually cracked.  Replaced that and before installing the cluster back in I got some liquid copper cleaner and cleaned the contacts on the cluster lights and the harness lights that plug into the cluster which were really tarnished.  The cleaned made them look bright and new.  Resolved the problem!  Thanks to all for their suggestions.
Phil