• Hi Guest!
    You can help ensure that British Car Forum (BCF) continues to provide a great place to engage in the British car hobby! If you find BCF a beneficial community, please consider supporting our efforts with a subscription.
    There are some perks with a member upgrade!
    **Upgrade Now**
    (PS: Subscribers don't see this gawd-aweful banner
Tips
Tips

TR4/4A Fuel and Temp Gauge NightMare! Help!

Share this page

Still shouldn't blow the chip, even if you short the output to ground. It is supposed to be fully protected (internal shutdown logic) against shorts and overload. Did you check that you are really getting 10.0 volts out?

Engine shouldn't run that cool, unless the thermostat is bad. Might be good to get some independent confirmation, like using an IR thermometer or even sticking a simple candy thermometer into the radiator filler neck.
https://www.harborfreight.com/1-inch-pocket-thermometer-46586.html

$150 is about right for a good TR3 gauge, either reproduction or original. Originals that still work are so rare that they bring close to the same price it costs to refurbish them.

One alternative is to pick up a cheap aftermarket mechanical gauge and use it at least until you get all the other issues sorted out. No one will mistake it for the original, but the look may not be all that bad. This one fit my TR3 dash and thermostat housing perfectly, no adapters required. Only modification was to hook up the light for it (one wire to the dash light switch).

I believe that's a Sunpro CP7975, and ISTR I paid around $25 at FLAPS. A quick search turned up this one on-line for $12 (plus S&H of course).
https://www.tooldiscounter.com/ItemDisplay.cfm?lookup=SNPCP7975&source=froogle&kw=SNPCP7975
 
Last edited:
Oh nice~! That doesn't look bad in there. Heck I have a bunch of sunpro and the like gauges, some new. I should check and see if they fit in the hole and housing.



In the short I got the wipers working, lights all around work including the brake lights. I don't think I've got reverse lights. I got the flasher and horn to work but it seems the column, wheel and column cover tube don't fit very nice. So the horn and the flasher is shorting in and out. Last if getting the heater to work. I'm pretty excited to put this dash all back together. I pulled the glass off the gauges and it should look pretty decent. Now it's time to twist my hands and body to hook up all the wires, grounds and clamps!

Anymore thoughts on a mech temp gauge?
 
The metal bezel Sunpro gauge's look period correct and are certainly affordable. I do suggest that for peace of mind you test the mechanical gauge by holding its expansion bulb in a pan of boiling water. The gauge should read fairly close to 212 oF but don't expect it to be dead nuts accurate.

In your 3:30 post you said:
"So I hooked up the temp gauge and it blew the 7810. I noticed that the input 10v tab on the gauge had been messed with. Looks like they left out the idolater when pulling the tab off the terminal. I'm guessing the gauge is grounding out the 10v causing the chip to blow."

A Smiths gauge designed for the voltage stabilizer should not have any connection between either terminal and the gauge case. Take your multimeter and check it out. If you find continuity between either terminal and the case, replace the gauge or try and figure a way to replace the missing isolator. However, as Randall said, with a short the chip should have shut down rather than blow.
 
Not sure if I mentioned this in this thread or not but my problem with the 7810's blowing was I was still pos ground. After I switched the bat cables and polarized the genny I was good to go. I had one single chip left and it was wired in to run both gauges and it's been working ever since!
 
That would certainly make sense!

Don't recall if Doug mentioned it; but the LM7910 is functionally the same as the 7810, except for positive ground. Just in case some other reader really wants to stick with positive ground :nonono:
 
Back
Top