Instrument and fuse issues...

[okartguy]

Tonight I removed the gauge cluster from my '75 parts car, with plans to install it in my '76 driver. I've already disassembled the cluster, so that I could set the odometer to the same mileage showing on my '76 (this was a major PITA, btw).

I *recall* that these instruments worked correctly when I brought the '75 home, but it's been about three years and I'm just not 100% sure. Is there any way to know the speedo is operating properly without testing it in-car?

Also, as far as the '76 goes, it has some interesting gauge problems that I would like to prevent from recurring. For example, the speedo needle is broken, and once underway the center merely spins 360º.

When I bought the car, the tach needle was permanently "pegged" at 8k. About halfway home from Memphis, the headlights flickered once on the highway. I looked down and noticed that the tach needle had swung back to zero, and also that my fuel and temp gauges were dead. Sure enough, the fuse was blown, and I've replaced it a couple times only to have it blow again within the next few minutes.

So. Am I asking for trouble installing a (supposedly) working set of gauges in the car? Or is this feasibly a short somewhere in the jacked-up instruments currently installed, and replacing them might solve the problem? Any insight is much appreciated. TIA-

[esty]

you can spin the speedo with a drill...that'll tell you if the needle moves & whether the odometer and trip meter work

[okartguy]

I thought about that... I hesitated because the cable shaft seems to move in and out slightly, as if it engages and disengages. I don't know much (read: anything at all) about the intricacies of VDO speedos, so I didn't want to make a judgement based on incorrect parameters.

I do know that the needle moves when I spin the input shaft by hand, so it at least has that much going for it.

[Mike Self]

Be advised that the speedo from the 75 parts car is for a 3.64 differential, and your '76 has a 3.91. And it's the speedo head that's geared differently, so the parts speedo won't read correctly. You'll need a speedo head from a '76.

As for the blown instruments fuse--I had the same problem with my '73, and after a bunch of head scratching I finally found the answer...the seat belt warning light is wired thru the same fuse (not on the factory wiring diagram)--and the light is connected through the seat belts and sensors in the seats...when they short out, they keep blowing that fuse. Check your wiring diagram, then unfasten the fuse box from the car and check for an extra wire on that fuse. That'll be the undocumented seat belt warning light wire. Clip and tape up, and it should solve your fuse blowing problem (i hope!)

cheers

mike

[okartguy]

Thanks for the tip on the speedo head... But considering I had a busted speedo with no needle in the car before, this one will at least be a cosmetic improvement! Anyway, I also noticed that the speedo has a 12/72 date stamp on the back, so that's probably even further off, not to mention I'm running 205/60-13s, which aren't exactly stock diameter. I'm mainly hoping for a working tach!

Oh, and I'll check the seatbelt warning wiring... I woulda NEVER thought of that. Thanks again-

Jon

[Mike Self]

way to tell: look on the metal housing (near where you spotted the "12-72") and there should be another stamping: W=x.xx. If the numbers match the numbers on the back of the broken speedo, they have the same ratio. Also, you'll find that 205/60x13 tires are within a few percent diamteter-wise of the original 168/80x13 tires.

As for the seat belt warning wiring, I discovered it by accident after several days of trying to puzzle out the problem, disconnecting one item after another on the offending circuit...when everything had been disconnected (according to the wiring diagram) and the fuse still blew, I took the fuse box loose and found the undocumented wire.

Hope that's it.

mike

[okartguy]

The '76 speedo was marked 1.39, whereas the '72 speedo is 1.28. Obviously a susbstantial difference. This proved itself out when I drove the car this afternoon; at 40 or so mph, the speedo is reading about 15mph too fast!

On a more positive note, along with the speedo, the fuel, temp and tach are now working. I replaced the fuse, figuring I'd at least see if the instruments worked before I started tracing out the short. Lo and behold, I've been driving the car all afternoon and it hasn't shorted out yet! Maybe it was the tach?

Unfortunately, neither the regular odometer or the trip odometer are working, so I guess I'll end up sending the original speedo off to NHS for a rebuild.

Anyway, thanks for the help!

[esty]

Anyway, thanks for the help!

there's like umpteen of them on ebay now....lot's of speedos tachs and complete clusters...you might find a good, reliable plug-n-play one for cheap....o2 stuff on ebay