Instrument cluster was burnt up

[Tallboy]

I've attached photos of what was fried in the cluster. Looks like they go to the voltage guage.... correct me if Im wrong. On the clip they are numbers 1- yellow wire and 17-red wire.

Any suggestions on whats going on here????? I went on a trip with the camper attached and two things happened. 110 degree days BTW. The turn signals went out and then when I got off the freeway they'd go back on. Also the oil pressure guage would fluctuate and go out.... then I'd slow down and it'd kick back in. wierd.
The temp guage doesn't work and hasn't since I put the truck back together.

It was a virgin harness and I adapted my 4 guage cluster to the 2 guage 2 idiot light that was originally on it. So that's about it. Then the truck wouldn't start and I replaced the coil. Alot of things going on but I replaced the coil and the truck runs. Now I have a burnt up guage cluster and need help figuring it out.
Thanks All for your help.

[Tallboy]

More pics

[Tallboy]

last one. This is opposite the alt guage

[68F250]

Oh boy, you can't just swap out a 2-gauge cluster for a 4-gauge. There's a lot of wiring changes in the cab and under the hood that need to be done first.

[Tallboy]

Well I need to explain a bit then. When i reconfigured it, I ensured that the 4 cluster wires were used for the oil sending, alt, temp and fuel guages and checked that against the factory wiring diagrams. So I did replace wire where appropriate. The cluster has been working fine for the last three months with no issues except the temp guage where the connection at the unit on the manifold has broken. I'll fix that soon.

Anyways I am confident that I did it correctly and took my time reviewing how a 4 went to a 2 cluster because I knew there were differences. The one thing I a concerned about it the resistor wire from the dash but I sodered it and have a good ground with everything.

[bluef250]

From the look of your gauge, my first guess is that power went to ground. Or second thought, you may have simply overwhelmed the printed circuit, it got hot, and burnt up. Did you limit the current to the amp gauge somehow? What size alternator are you running? What size wires did you install to the amp gauge?

[68F250]

Oh, ok. Yes it does look like you fried the circuit to the ammeter. How did you rewire it compared to the alt. light?

On alt. light clusters, 12V power is applied to the bulb with the key in the "On" position and the other end goes to the "I" terminal on the voltage regulator. The stator on the alternator is also connected to the "S" terminal on the voltage regulator.

On ammeter clusters, one end of the gauge goes to the battery side of the starter solenoid and the other end of the gauge goes to a tap in the middle of the heavy wire that runs from the alternator "Batt" post to the battery side of the starter solenoid. (JMO I think you could run that wire directly to the alternator "Batt" post instead of where they tapped it.) Also the stator on the alternator is not connected to anything, the "S" terminal on the regulator goes directly to the ignition switch and gets 12V in the "On" and "Start" positions only. Nothing connected to the "I" terminal.

Those are the differences that need the changes to swap clusters. The wires to the ammeter don't need to be heavy, it's only reading shunt current but I would fuse both wires with 3A fuses just in case one of them ever shorts out.

[68F250]

Oops!

Was editing the previous post and hit "Quote" instead.

[rjewkes]

what is the obvious diff between the two and four volt circuit boards?



if you can rewire it i beleive i have the corect one for all guauges and no dummy lights.

[ToughOldFord]

Oh, ok. Yes it does look like you fried the circuit to the ammeter. How did you rewire it compared to the alt. light?

On alt. light clusters, 12V power is applied to the bulb with the key in the "On" position and the other end goes to the "I" terminal on the voltage regulator. The stator on the alternator is also connected to the "S" terminal on the voltage regulator.

On ammeter clusters, one end of the gauge goes to the battery side of the starter solenoid and the other end of the gauge goes to a tap in the middle of the heavy wire that runs from the alternator "Batt" post to the battery side of the starter solenoid. (JMO I think you could run that wire directly to the alternator "Batt" post instead of where they tapped it.) Also the stator on the alternator is not connected to anything, the "S" terminal on the regulator goes directly to the ignition switch and gets 12V in the "On" and "Start" positions only. Nothing connected to the "I" terminal.

Those are the differences that need the changes to swap clusters. The wires to the ammeter don't need to be heavy, it's only reading shunt current but I would fuse both wires with 3A fuses just in case one of them ever shorts out.

Okay, maybe I'm learning something new here, I was about to jump in and and dispute that, (in a friendly manner of course, ) and here's why:

In all the Mopars and Ch*vys I've worked on the amp meter had very heavy gauge wires going through them because all current was routed through them. If you pulled one of the wires to the amp gauge you lost everything, the engine would quit and you'd have no lights, ignition, accessories, etc. The only thing not routed through the gauge was the starting system for obvious reasons.

However, I happen to have a instrument cluster from a '69 F series right by my desk at the moment so I took a look at it's amp gauge and I see that the only thing running to it is that cr*ppy membrane. Obviously that can't hold much of a draw so Barry must be right, it's just something new to me. Maybe that explains why these OEM Ford amp gauges never seem to move much one way or the other.

[68F250]

Yeah the Mopars had a terrible system. The ammeter had the shunt internally so ALL of the current ran thru the wires, a real fire hazard. If you were lucky only the firewall connector would melt off, otherwise the dash would burn up, or more. Shelbys had a similar system with all the current going thru the gauge.

The Ford system had the ammeter shunt located externally, in the alternator harness. Only a fraction of the current runs thru the wires to the gauge. It's a good idea but they designed it on the conservative side so it doesn't deflect very far. Over time the added resistance build up in the wire connections, fuse holders and connections to the gauge cause it to deflect even less, to the point that it barely moves at all.

I guess enough Tbird owners complained to Ford about it that they redesigned the circuit for '70 to really move the needle. They did such a good job that a year later Ford came out with a service bulletin for the Tbirds to explain to customers that the extreme meter movement was normal. Guess you can't win, kinda funny.