Black Fuse-like Electrical Connector?

[samblnc]

Working through an electrical issue (resolved), I encountered the connector shown in this image. It’s located next to the windshield washer pump. Opening it up revealed a glass protruding on one end, and a small metal tab protruding out of it. Putting a 12 V tester to both ends showed power on both. Anyone know if this is part looks to be intact and what its function is?

1973 C10.

Thanks.

 

[Rickf]

Sounds like a glass fuse.

 

[Jgonick]

73 wire diagram shows a fuse

 

[Randy and Easton]

@RustyPile will be along here shortly to fill you in but it’s the 3A fuse for the Ammeter in the dash if you still have it.

We had same set up on our 1976 )which should have been a volt meter) Nick was overly helpful in walking us through that setup and function. Easton eventually wanted a volt meter to stay in line with the year so we did the taking power from temp gauge setup and it’s been working correctly ever since. We removed the fuse and it’s just tucked away.

Randy and Easton

 

[samblnc]

Thanks for confirmation.

 

[Randy and Easton]

Do you indeed have an ammeter?

 

[samblnc]

You must be registered for see images attach

Factory gauges.

 

[samblnc]

73 wire diagram shows a fuse

Thank you

 

[75gmck25]

It’s one of two fuses for the ammeter. The 2nd one is over on the other side of the engine compartment.

 

[samblnc]

With it disconnected like in the pics, I read 12 volts to ground on the left side. Just as a check, I put the meter on the right side, and also measured 12V to ground. Is that common? Expected 12 volts on one side. Is that an indication of another problem somewhere down the line? Backfeeding voltage?

 

[Randy and Easton]

@samblnc No. It is a continuous loop that measures the amps along that circuit. Nick can explain the intricacies of how the length of wire in the loop measures the amps at the gauge but power is always in that loop.

Randy and E

This is how we replaced ammeter with a volt meter.

 

[75gmck25]

In the early squarebody trucks they used the wiring in the truck as a shunt with a known resistance, and an in-dash ammeter to “calculate” amperage. That avoided the risk of running full alternator amperage up to the dash and back to the engine compartment.

The dash gauge has the voltage at one fuse holder on one side, and the voltage from the other fuse holder on the other side. The fractional difference in the two voltages is used to “calculate” and display amperage on the gauge. It’s only accurate if you know the resistance of the shunt (which is the wiring in the truck), but as the truck gets older the wiring resistance changes. It will never be accurate, so just change to a voltmeter.