Speedo and Tach off and on while driving?

[MrMazda92]

Brandi has been having an issue with her electrical lately, and it's something that has me a little baffled.

Ever since the weather reached a seasonal high(80+ degrees), her speedometer and tach have been dropping to zero and then climbing upwards again. They do so randomly, sometimes concurrently, other times individually.

This originally happened when the stereo was playing and the A/C was on max... Leading me to believe that the electrical system was being overburdened, and that the alternator couldn't keep up, thus allowing the battery to completely drain.

On a few occasions, the car has actually stalled while driving. Popping the clutch promptly restarts the car, but the gauges do NOT function immediately after a pop start.

Suggestions have ranged from voltage regulator to Alternator, groundwires to disty failure.

Originally the car was having a hard time starting up after these incidents, but a quick check of the grounding points and charge wire led me to a loose charge wire on the alternator. After being torqued down a bit, the starting problem went away 100%.

There is no loss of power anywhere in the RPM range, no dimming of the headlights at night, and no trouble starting. The battery currently in the car tests out perfectly, and we have tried another battery in known working condition.

Any suggestions?

[Evo_Spec]

what solutions have you actually tried? just battery?
cause it sounds similar to my dead alti situation, it would die when i braked but i could start the car again after and so i just drove without the brakes to the junkyard and got a new one and it was as good as new.

[MadMaX3]

We're going to put in a different alternator and see if that helps any.. But when I had my alternator tested they said it was running "beautifully" so.. I dunno..

[ganue]

I'm guessing ignition switch or the 15A fuse connection to the cluster circuit. Can't explain the stall but try this weird thing. If it happens enough, have her drive around with the parking brake set such that the brake light goes on but the the actual brakes are not engaged. Maybe temporarily loosen the cables for this.

Why?

Because the brake light on the cluster is fed from the same 12V feed as the rest of the cluster, and no other indicator would react as fast as the tach and speedo (fuel and temp are heavily filtered so maybe they wouldn't act like the tach and the speedo anyway). So, the brake light being on all of the time just will help isolate the electrical issue.

If the light flickers in concert with the tach and speedo, you have a 12v feed issue to the cluster. If the light does not flicker when the tach and speedo do their dance it could be the ground circuitry or local to the cluster.

If you get real clever you could do the same thing on the ground side. Use one of the cluster's ground signal (circuit 2A or 2G) and tie that to the low side of the brake light and do the same test (but you won't actually need the brakes on this time because you are grounding the low side of the lamp to pin 1G). But this time if the brake light flickers with the tach and speedo, you have a loose ground. If not - low side of the tach and speedo are problematic on the cluster.