Spitfire heat guage - Spitfire

[deegeeguy]

I've got an electrical "issue" somewhere in my 77 Spit 1500. When I turn on the key, the heat guage goes to halfway automatically, then it starts registering from there. This means it redlines really quickly - like before I get out the driveway.

The gas guage is working fine - and all other electrical components seem OK - or at least they're working well.

Can somebody who obviously has more experience than I do give me some sense of where I might begin looking?

Doug

 

[Eric]

I'd suspect the sender. Disconnect the wire from the sender and turn the ignition on. The gauge should read zero. Now ground the sender wire. The gauge should read full hot. If so, your problem is likely the sender. If not, you problem lies elsewhere.

 

[deegeeguy]

Eric - thanks for the suggestion. Did what you suggested but nothing changed withe gauge - grounded or not. The fan kicked in (electrical cooling) when the sender wire was grounded but the gauge never budged with ground or not.

OK - I guess I'll have to start messing about with auto electrical. ;-)

 

[TR4]

On my TR4, there is a voltage stabilizer that is connected to the heat guage. I had to change that to solve my guage reading hot. The fuel guage is also connected to the stabilizer but that was working fine before and after the change.

 

[deegeeguy]

OK - I'll go try and sort that out. Never a dull moment with this little beast. I do appreciate the suggestions from you guys. I'll let you know what I figure out.

 

[guzzul]

There are only 4 things that should cause this: the gauge itself; the voltage stabilizer that feeds the gauge; the sender; or the wiring in between these components.

If the fuel gauge works ok, then the voltage stabilizer is probably ok. If the fuel gauge is acting funny too, then the voltage stabilizer would be my guess.

If, as you say, there is no change at all when you unplug the sender wire, and no change at all when you ground the sender wire, then the sender is not the likely problem either.

So that leaves you with the gauge itself, or the wiring, or possibly the terminal connections at the gauge. I would suspect its probably the gauge. But to check any further you need to drop open the centre panel so you can get at the gauge and wiring connections.

The Light Green wire on the back of the gauge comes from the voltage stabilizer. It should read about 10 volts on a voltmeter if you check it with power switched on. The Green wire with Blue Tracer goes to the sender unit. If you ground this wire at the sender, and unplug it at the gauge and check it with an ohmeter, you should have continuity to ground. If so, your wiring should be ok, and the problem is with the gauge itself.

When you do all this, it would be wise to unplug the White/Slate wire at your ignition coil, because the electronic ignition does not like to have power on while the engine is not running.

 

[Lionheart]

The fan kicked in (electrical cooling) when the sender wire was grounded but the gauge never budged with ground or not.

So, you have an electric cooling fan in your 77 Spit? This may be a source of confusion...the 77 should have an engine-driven fan.

Perhaps the aftermarket electric fan was wired such that it draws extra current through the gauge?

Which sending unit did you pull the wire from?