Temp senders

by Abashore1980 Sat Mar 19, 2016 3:34 pm

Ok, well I've been delving into the rats nest of mickey-moused wiring in the GP ('76 SJ 400 ci). It seems like there are way too many temp senders and I don't know why. The temp gauge has never worked since I had the car last spring. While tracing the wiring for the kickdown, I found that it was patched into the sender on the left side cylinder head!

My question is why are there 3 on this car (2 on cyl heads, 1 on intake)? Which one should I use to get engine temp to my gauge (rally gauges)?

Temp senders Photo_11

Thanks in advance guys!

by pila Sat Mar 19, 2016 7:09 pm

Does that car have the automatic temp control air conditioning ? If so, maybe the extra senders have something to do with it

by Abashore1980 Sat Mar 19, 2016 8:02 pm

It has AC, but not automatic temp control.

by thatfnthing Mon Mar 21, 2016 10:22 am

I'd guess the 'why' of 3 factory temp senders would be in the wiring diagrams for the 76 Pontiacs, which I don't have.

Regardless, which to use for your gauge will depend on two things:

1. The coolant willl vary a few degrees depending on where you take the reading from. Are you looking for a worst-case coolant temp or the 'average' coolant temp? If the former, use the one in the head. If the latter, use the one on the intake.

2. The sender/gauge calibration. Thermistors can vary wildly in their ranges, and the sender you use must match the gauge, otherwise your gauge won't read anything even close to right (if it reads anything at all). If you're using a factory gauge, you will need to use the appropriate factory sender (again, the wiring diagrams would come into play here). If aftermarket, use the sender that comes with the gauge (or the one specified by the gauge manufacturer).

by 73ss Mon Mar 21, 2016 5:37 pm

The driver side head is the one. It looks to be the correct wire as well. With the key on, momentarily ground this wire. the gauge should peg to full hot. Not sure why that would be spliced into the kickdown circuit.

The pass side head looks like the low speed fan control. Intake?? maybe some sort of smog device, maybe the intake or engine was swapped at some point? Maybe it is a broken vacuum switch?

by Abashore1980 Fri Mar 25, 2016 9:54 am

Thanks for the replies guys. I do have the wiring diagram for the car, but it only shows one temp sender, connected via a dark green wire, which is what is connected on the drivers side head. That same dark green wire was teed off and run into the kickdown switch, because the last person to work on the car is a complete idiot.

That being said, I will use the drivers side head sender running into my factory temp gauge. Not sure if it works yet after disconnecting from the kickdown, as the battery is out. I have a new intake (performer RPM) and carb (1406) that I'll be bolting on soon. I'll just plug the hole for the intake sender.

Thanks again!

by thatfnthing Fri Mar 25, 2016 10:03 am

Abashore1980 wrote:That same dark green wire was teed off and run into the kickdown switch, because the last person to work on the car is a complete idiot.

I would love to know the thought process on that one. Just what exactly was that supposed to do?

by Abashore1980 Fri Mar 25, 2016 1:31 pm

thatfnthing wrote:
Abashore1980 wrote:That same dark green wire was teed off and run into the kickdown switch, because the last person to work on the car is a complete idiot.

I would love to know the thought process on that one. Just what exactly was that supposed to do?

I don't think they meant to. At least I hope not. The kickdown switch was bad anyway! I only found the error by tracing the wire from the switch through the firewall and the wire loom. It was tied into the temp sender on the pass side head, which was also teed into the driver side temp sender. The underside of the dash looks like a rats nest of wires. At least some go to the right place.

Temp senders 12688173_1582584015393094_2973608022579774875_n

Temp senders 12688173_1582584015393094_2973608022579774875_n

You should see the body work if you think that's bad.

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