Soaring Temp Gauge - Electrics

[SimonO]

My temp gauge goes straight to the red when the engine is started. This is obviously electrical, but what to check first...? I'd rather not remove the dash if there's an earth in the engine bay etc.

Any help for an idiot would be appreciated...

http://persistentworktriumphs.blogspot.com/

[Stag76]

You could disconnect the wire from the sender in the thermostat housing, and if the gauge still reads maximum, it could be the gauge itself, or a short to ground in the sender wire. If it doesn't move, it could mean that the sender has failed. You can then check the sender by measuring its resistance using a multi-meter.

TR7 Convertible
Sprint Motor
MegaSquirt EFI

[slider]

hi pull the connector off the sender on the engine and with some one sat in the car(with the electrics on)just touch the connector to earth,guage should not move until you touch connector to earth(engine)and then should go to hot, this shows sender is u.s. If it goes to hot even when sender is dissconnected the guage could be u.s or wireing is shorting somewhere. Take heart though the gauges are quick/easy to remove[;)]

[SimonO]

I think my dash electrics are shot anyway as my fuel gauge is tempremental, clock rubbish, rheostat dodgy and the live for the cigar lighter isn't. I also have 4ft of cable where the stereo should be.

I have a spare dash pod, some of Odd's LEDs and am now looking for a new loom to sort the whole lot out.

It'd be just my luck that the car actually overheats when I'm thinking it's just the sender unit!!!

http://persistentworktriumphs.blogspot.com/

[SimonO]

New sender being ordered - thanks!

http://persistentworktriumphs.blogspot.com/

[FI Spyder]

<blockquote id="quote"><font size="1" face="Century Gothic, Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote"><i>Originally posted by SimonO</i>

I think my dash electrics are shot anyway as my fuel gauge is tempremental, clock rubbish, rheostat dodgy and the live for the cigar lighter isn't. I also have 4ft of cable where the stereo should be.
<hr height="1" noshade id="quote"></font id="quote"></blockquote id="quote">

Sounds like all contacts under dash need to be cleaned rather than going to try to correct one problem a time. I took mine out and cleaned every connector there including the copper contact strip on the plastic circuit sheet and every bulb contact. Do it once, do it right and never do it again. If the clock is still dodgey, there is a fix that will turn it into a reliable time piece (do a forum search for the website link). Watch what you try to clean the rheostat with. It is a coil wire with resistance coating. I put mine in a molasses/water solution (gets rid of rust) and it ate the resistance coating, now I have full brightness regardless of switch position.

These cars are 30+ years old with unsealed electrical contacts (except for newer light lift mechanisms and a systematic cleaning of electrical terminals with a thin coating of dielectric grease will get rid of a lot of present and future electrical gremlins.



TR7 Spider - 1978 Spitfire - 1976 Spitfire - 1988 Tercel 4X4 - Kali on Integra - 1991 Integra - Yellow TCT

[sheppjr]

It's not the sender but rather a break/short on the blue printed
circuit on the back

[sheppjr]

Sorry for the inadvertent send. The problem is with the
printed circuit on the back of the instrument cluster. I had
the same problem last year and it was a short or open on the
ground side of the circuit. You need to replace the printed
circuit to solve your problem.

[RadioGuy]

<blockquote id="quote"><font size="1" face="Century Gothic, Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote">You need to replace the printed
circuit to solve your problem.<hr height="1" noshade id="quote"></font id="quote"></blockquote id="quote">

Or run a jumper wire, taking the printed conductor out of the equation.[:0]


Maintained on Saturday…Drive on Fun-Day !!! 1976 FHC - 1980 DHC

[SimonO]

I'm going to build a new dash on the bench which will allow me to replace anything duff and clean everything before putting in the car - just got to get hold of a loom too...

http://persistentworktriumphs.blogspot.com/

[rosey]

I had a similar problem with gauges and it turned out to be a high resistance on the PCB, the problem occured whenever the dashboard lights were on, the gauges then went full over until the lights were turned off again.
It's difficult to diagnose these sorts of problems (I should know as I am an Electrical Engineer by trade) and the only way I cured it was to use a replacement PCB, I have a few spare dashboards and gauges so I am lucky in this respect.
The PCB they used for the TR7 was a new idea in the early 70's and doesn't seem to be ageing well after 30 odd years (a bit like me[:)])


"Do or Do not, there is no try" - Yoda

1981 Purple Grinnal 2.0L
1980 TR7 Persian Aqua Drophead.
Honda Civic Type R GT in red!

[sheppjr]

Rosey is right. The problem intially occured when I turned the lights on. The interesting thing was I could actually reach up behind the dash and press on the printed circuit board behind the temp gauge and make the temperature gage move from high back to normal and then back to high.

Richard