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Topic: Fuel gauge and speedo? (Read 1239 times) previous topic - next topic

Fuel gauge and speedo?

Ok, guys...  this one is making me mad.  I hate it when I can't get the simple stuff to work!

I'm still working on wiring up my SN cluster.  Everything is working except the fuel gauge and speedo.  Here's what I've done:

The 'circuit overlay' (the sheet with wiring printed on it like the back of our fox gauges) for the 95 mustang cluster has writing in it telling you what all the pins go to.  The speedo has: batt, run, sig and ground.  So, I connected a 12v constant to batt, 12v run source to run, dk gr/wht from the vss to sig and ran the ground pin to a generic cluster ground.  Double checked everything (except idk how to check the signal from the VSS - but it worked a few weeks ago when I pulled the fox dash).  As a side note, I also lost my back-up lamps when doing the SN dash swap and both the VSS sig and the back-up switch wiring go through the harness that goes through the trans hump and to the trannny.  I need to check all that (the connector is connected behind the dash)...

Next, the fuel gauge.  Same kind of deal; 12v run source and ground to the proper pins and the yel/wht wire at the cluster to the sig for the fuel gauge.  I'm pretty sure the senders use the same signal.  The strange thing is, when I pull power from the cluster the fuel gauge goes to 1/4 tank, but when I turn the car on it goes to E (as if it's operating backward.  Here's the diagrams I'm using:
1988 Thunderbird Turbo Coupe
'89 5.0 w/ ported intakes, Mallory Adjustable FPR, BBK shorties and H with 2.5" Flows, 130 amp 3G, 89 Mustang comp/wiring, Aluminum radiator w/ elec fan, T5 trans, King Cobra clutch, 3.55 gears, 13" Cobra brakes (front), Wilwood prop valve, Mustang A-arms, Front Coil-overs, MM CC plates, Silver 17x9 R's, 03 Cobra IRS, Aluminum DS, 2002 Mustang dash/console etc..., custom leather seats

Fuel gauge and speedo?

Reply #1 –
The EVTM page is for a basic instrument panel.
Your second drawing looks like it's for an electronic panel.

Go to page 144 in the EVTM for an electronic panel. Compare the fuel gage senders. For the basic panel the resistance drops as the tank fills. Electronic panel the resistance increases as the tank fills.

So if you change from one type of panel to the other the gage will read backwards. You will have to change the sending unit.

Fuel gauge and speedo?

Reply #2 –
Page 129 is for the standard fuel gauge (non digital) and the mustang didn't have a digital option so both of these diagrams should be for the same type of gauge.  But maybe the sender is still backward...?  If I go look at both ('bird and 'stang) at the auto store, how can I test them (in store)?

As for the speedo, next step is connecting it to 12v and a signal generator.  That will atleast tell me if it's working...
1988 Thunderbird Turbo Coupe
'89 5.0 w/ ported intakes, Mallory Adjustable FPR, BBK shorties and H with 2.5" Flows, 130 amp 3G, 89 Mustang comp/wiring, Aluminum radiator w/ elec fan, T5 trans, King Cobra clutch, 3.55 gears, 13" Cobra brakes (front), Wilwood prop valve, Mustang A-arms, Front Coil-overs, MM CC plates, Silver 17x9 R's, 03 Cobra IRS, Aluminum DS, 2002 Mustang dash/console etc..., custom leather seats

Fuel gauge and speedo?

Reply #3 –
, ok, well there goes that idea.  No one (rock auto, autozoo, kragen) shows a fuel sending unit for the turbo coupe (3.8 and 5.0 only).  I would assume they'd be the same, but why the same outcome at all parts suppliers?  I also checked the 88 thunderbird 5.0, 88 mustang 5.0 and 95 mustang 5.0 and autozone shows the same part for all three for sender and tank...  so, if the 88 TC used the same sender as the Sport, things should be working fine.
1988 Thunderbird Turbo Coupe
'89 5.0 w/ ported intakes, Mallory Adjustable FPR, BBK shorties and H with 2.5" Flows, 130 amp 3G, 89 Mustang comp/wiring, Aluminum radiator w/ elec fan, T5 trans, King Cobra clutch, 3.55 gears, 13" Cobra brakes (front), Wilwood prop valve, Mustang A-arms, Front Coil-overs, MM CC plates, Silver 17x9 R's, 03 Cobra IRS, Aluminum DS, 2002 Mustang dash/console etc..., custom leather seats

Fuel gauge and speedo?

Reply #4 –
Hmm, I would take a DMM at your sig wire for the fuel.  See if you are in the 60-86ohm range.

If you are, you know your sender is putting out what you expect.
Next you would need to find what range the stang used (And its respective Higher R means (empty or full).

Even if the stang is reversed direction from what your bird expects, you can still get it to work by re-wiring the sender.  Switch the  ground and sig lines on the float and it will reverse its direction.

If your range is wrong, you can add additional R in parallel to shift the Range lower in Resistance. 

Let me know what you find out.

Fuel gauge and speedo?

Reply #5 –
Ok, sweet!  I figured I could reverse it somehow.  I'll test it tomorrow...  can't believe it'd be off the normal 'ford' range.
1988 Thunderbird Turbo Coupe
'89 5.0 w/ ported intakes, Mallory Adjustable FPR, BBK shorties and H with 2.5" Flows, 130 amp 3G, 89 Mustang comp/wiring, Aluminum radiator w/ elec fan, T5 trans, King Cobra clutch, 3.55 gears, 13" Cobra brakes (front), Wilwood prop valve, Mustang A-arms, Front Coil-overs, MM CC plates, Silver 17x9 R's, 03 Cobra IRS, Aluminum DS, 2002 Mustang dash/console etc..., custom leather seats

Fuel gauge and speedo?

Reply #7 –
hahahaha...  that has proven to not work on quite a few occasions, huh?

Anyway, I was thinking about reversing this thing again and I'm confused how it would work.  Whether I have it connected as normal or I reverse the the wires at the sender it's still just a ground for the gauge which runs through a variable resistor.  The only way to actually reverse it would be to modify the sender so it acts on the variable resistor opposite of what it does now...??
1988 Thunderbird Turbo Coupe
'89 5.0 w/ ported intakes, Mallory Adjustable FPR, BBK shorties and H with 2.5" Flows, 130 amp 3G, 89 Mustang comp/wiring, Aluminum radiator w/ elec fan, T5 trans, King Cobra clutch, 3.55 gears, 13" Cobra brakes (front), Wilwood prop valve, Mustang A-arms, Front Coil-overs, MM CC plates, Silver 17x9 R's, 03 Cobra IRS, Aluminum DS, 2002 Mustang dash/console etc..., custom leather seats

Fuel gauge and speedo?

Reply #8 –
Never mind. It was a dumb idea.  I just looked at your diagram and realized that ford ties the wiper on the pot to ground.  (That sounds horrible)  If you had access to all three points on the pot independently, you could re-wire it.  Ignore my silly suggestion.