Little fuse inline in dr side eng comp harness

[Low Elco]

What is it for?
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[zeeklu]

I think it's for the amp gauge. Chris
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[john]

There is also one on the pass side. 4amp.

[1972SUPERSB]

Isn't the fuses for the front headlights and parking lights?
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[70STOVEBOLT]

Both fuses are for the stock ammeter in the dash. There are other threads on here that talk about this. My ammeter did not work for years and I replaced both of those fuses and it has been working since.

[VetteVet]

Yes these are the fuses for the battery gauge in the full gauge truck harnesses. There are no fuses for the headlights except the fusible link from the battery to the terminal on the right passenger fender.
There is a fuse in the fuse panel for the Stop/turn/tail lights. I'm not sure if the front lights are in that circuit without looking at the wiring diagram.

Here is a good diagram with the fuses circled. This has all been covered in the electrical forum dozens of times.

[SS Tim]

The headlamp switch has a built in circut breaker.
Might want to read up some on your truck.
http://67-72chevytrucks.com/vboard/s...d.php?t=544915

[VetteVet]

Originally Posted by SS Tim

The headlamp switch has a built in circut breaker.
Might want to read up some on your truck.
http://67-72chevytrucks.com/vboard/s...d.php?t=544915

Forgot that little bugger. Guess that makes me totally ignorant about my truck.

[SS Tim]

Vettevet, you do great with the electrical problems. Most of the time I just sit back and read. But the 15A circut breaker is not a well known fact and not on most of the schematics. The schematic you used in fact just shows the wires going to the connector and not the fact that the circut protection is in the switch itself.

My response was intended as two sperate and distinct statements.
The fuses and circut breaker are in the owners handbook that everyone really should have.

As far as forgetting stuff, we all do and often. Most posts often need an edit to correct my WTF moments of missing picture, information or spelling disasters.

[Low Elco]

Thanks for the answers! I've had 5 of these trucks and never knew it was there. Amp gauge still dead, though. Hmmmm.
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[VetteVet]

I'm assuming you're referring to the yellow truck your Dad owns, and not your 87.
Check the cluster feed fuse in the fuse panel and if that's good then check for 12 volts on each side of the ammeter. If you don't get voltage on the ammeter then check the two black wires on the cluster plug at pins 1 and 12. If you get nothing there then one or both wires are open from the battery connection and the alternator, regulator. battery junction .

You also need the shunt wire between the battery and the alternator junction for the ammeter to be able to read differential voltage between the battery and the alternator.

refer to my diagram I posted above for the shunt and the wiring to the firewall block.

Here's the schematic for the inside of the cab showing the connections for the cluster plug for the dash gauge cluster and the idiot light cluster. The plug connections for the gauge cluster is on the top of the diagram and the idiot light connection is on the side of the diagram. Notice the schematic doesn't show the circuit breaker for the head lights like Timmy said and that's because the breaker is inside the headlight switch.



here's the cluster plug for the gauge cluster. Notice 1 and 12 are the ammeter wires. The wires are numbered starting at the lower left with 1 at the bottom and 6 at the top, then on the right 7 at the top and 12 at the bottom. Your plug should also be numbered to match.



Here's the back of a dash cluster showing the cluster connection and the copper strips to the ammeter on the lower right.




And here's the schematic that shows the wires from the cluster plug see pins 1 and 12 that go to the ammeter. These wires are both positive so don't wire to the negative on either or you'll burn up the gauge. The gauge cluster and the gauges must be grounded in order for them to work so check that you have a good ground on both. The gauges to the cluster and the cluster to the cab ground.

[Low Elco]

Wow, thanks! If you read the thread on the yellow truck, you know I've got bigger fish to fry at the moment, but thanks for the detailed reply! I've owned 2 of these, he's had 3, I've done all the work on 2 of those. The temp gauge is dead as well, I believe the printed circuit is bad, going off your excellent advice and testing guide, so thanks in arrears. It runs at the moment. Another electrical question, if I may. I have a problem with the hvac fan, with a 30 amp fuse in, (I know it's too big, it was all I had) it'll almost melt the connector. Is there a resistor set for the fan switch and where? Thanks again for the great advice, I can wire a stereo and a trailer, but I'm otherwise electrically useless.
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[VetteVet]

Originally Posted by Low Elco

Wow, thanks! If you read the thread on the yellow truck, you know I've got bigger fish to fry at the moment, but thanks for the detailed reply! I've owned 2 of these, he's had 3, I've done all the work on 2 of those. The temp gauge is dead as well, I believe the printed circuit is bad, going off your excellent advice and testing guide, so thanks in arrears. It runs at the moment. Another electrical question, if I may. I have a problem with the hvac fan, with a 30 amp fuse in, (I know it's too big, it was all I had) it'll almost melt the connector. Is there a resistor set for the fan switch and where? Thanks again for the great advice, I can wire a stereo and a trailer, but I'm otherwise electrically useless.
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First off what 's wrong with the temp gauge?
second is your truck with or without AC The sans AC fan uses a 10 amp fuse and the AC truck uses a 25 amp as you know because you said 3o was too big.
They both have resistors to control the fan speeds. The AC fan is more powerful or so I've read. I'd hazard a guess that the fan motor is drawing too much resistance and heating up the connector.
The non AC resistor looks like this.



It is located in the heater duct


The AC circuit looks like this.



Hope this helps

[Low Elco]

Been a bit since I checked it, but as I recall it was shorted at the back of the gauge in the cluster. I'd have to try again to remember. It flips back and forth ok, but won't read. It's non ac, thanks for the info on the resistors, I bet they're bad. They crapped out on my 05 Silverado and melted the connector the same way. The blower motor is new, changed during the cab swap. Thanks again!
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