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Discussion Starter · #1 ·
We're planning to remove and replace the amp gauge this weekend from a factory set-up. The gauge never moves from the 12:00 position. Battery was dead one time and it still didn't move. It has never worked since I've owned the car - whether the car is running, or not.

Before we rip the dash and gauge cluster apart, is there anything else that should be checked before we dive in?

I seem to recall a thread I saw about something near the battery that could have gotten zapped by an inadvertant ground that would cause the gauge not to work. I did a search, but couldn't find it again.

Assuming we still have to replace it, any do's and don'ts for removing the cluster and gauge from the cluster? I know we have to be careful with the lens so as not to scratch it. Anything else? Anything electrical?

Thanks for the help!!

Andy
 

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More than likely the etch on the circuit board of your gauge cluster is fried. The underhood amp gauge connections are one at the terminal block in front of the battery and the other at the horn relay. I forget which is which but one is black and the other is black with white stripe. A plain ole AA flashlight battery is enough to cause the amp gauge to deflect to see if it is working. I would remove the dash pad and inspect the traces that go from the gauge connector to the amp gauge. If they look ok, remove the connector and put a AA battery across the two traces. If that checks out, ohm out the under hood amp gauge wires. I don't think either one of them is fused or fusable links.
 

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Not sure about a 70, but my 67 service manual shows a fusible link on both ends, at the junction block and another at the horn relay
 

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Discussion Starter · #4 ·
Thanks for the replies, guys!

Steve - If the circuit board is fried, where's the best place to get a replacement. Our sponsor doesn't carry them that I can find. Year One has them for $85.00. Any other reputable sources that might be more reasonable?

Also, I've been doing some reading about this topic on other threads. I've seen quite a few references to fire risk from an amp gauge. Some guys said they have gone to volt meters instead because of the risk. The discussions always seemed to be about after market set-ups, but what fire risk is there when you replace a factory amp gauge with another factory unit - or a re-pop gauge? Are we walking an electrical tight rope doing this? We certainly are not pros!

Thanks again!

Andy
 

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One cheap option to repair broken etch is to remove the wire from the gauge connector and put a terminal on it and run it straight to the amp gauge terminal. IF you do this then there is a fire hazard and you need to fuse the connections at the battery terminal block and horn relay. A 5 amp fuse is plenty. I have bench tested 70-72 amp gauges and they will peg at about 3 amps. Factory amp gauges are really volt meters, they register the voltage drop across a known lenght/size of wire (hence you know what the resistance is) that runs from the battery terminal block across the radiator support to the horn relay. So only a small amount of current actually runs THROUGH the gauge. In my opinion there is no fire hazard because the circuit board etch serves as a fuse (about 30 amps will burn it open). I guess the etch burning open could cause a fire if it was touching some wiring.
I have done several light to gauge conversions and I always add a fuse at the horn relay and terminal block just to protect the etch and for safety. I have seen other posts that suggest using fusable links but they allow way to much current before they blow. They only protect the wire and will still burn up the circuit board.
 

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Discussion Starter · #6 ·
Steve

Thanks for the info, but after all I have in the car (money and sweat), sounds like $85.00 is worth it! Why take the risk of something so catastrophic happening? I'd never forgive myself!

Thanks again for the information!


Andy
 
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