kcfong2

My 1981 US Spec 5spd uses temperature time switch part number 92860510100. Per the WSM (24-17) at less than 86F, I should be getting readings of 0-ohms on terminal G to ground, and 0-ohms on terminal W to ground and between 25-40 ohms across both terminals. I'm getting 37ohms on G and 0 ohms on W, and 37ohms across G and W. Since G is out of spec, I figured my switch was bad, so I ordered a replacement. The new part, per the Bosch website has been superceded to part F026T03100, and uses electronics vs the old bi-metal. Visually, it is much longer than the original switch.

I received the new one today, and tested it per the WSM, but got some weird results... I get 5.46k ohms on G to ground, and an open circuit on W to ground and open circuit across leads.

I'm wondering if the new style switch, due to its electronics, cannot be tested like the old style bi-metal.

Can anyone confirm this? And if it doesn't test as per WSM, how can it be tested?

I don't want to send it back (yet), thinking that it just doesn't test the same, but need confirmation.

The Forgotten On

You need the old bi metal switch, the electronic one will not work and could possibly damage the car.

You can find a bi metal one. NOS ones on Ebay from time to time and good used ones as well.

kcfong2

Thanks Blake. I believe you, but is this from experience or hearsay? I'll definitely not try it, but everywhere I checked said the new style is a direct replacement for the old one. Guess I'll hit up my friends at 928 Intl for a used one, or Roger for a new one.

The Forgotten On

It's partially from experience as my 81 has the same system. It sends current to the cold start injector as its only job. It doesn't communicate to the computer at all.

I don't think the newer style can handle the amount of current needed.

kcfong2

Blake, just sent you a PM.

Landseer

IIRC, There is a tech bulletin that says the WSM has the wire identification reversed for the temp time switch.
So you may want to review that if you are going by the book on this one.

I've posted it before, and can dig it out again from tech bulletins in the Morehouse cd set, but it will have to wait until I get home from work

Majestic Moose

For what it's worth, I have been using the new longer style switch and it works fine.

j.kenzie@sbcglobal.net

For what it's worth, a few years ago I posted my elimination of the thermotime switch by grounding one pin in the connector .It makes the cold start injector function when the key is in the start position. Works great. I was happy I did this when I'm added my supercharger, because the connector doesn't fit.
Good luck,
Dave

Landseer

Looks like the mislabeled terminals issue was limited to early wsm wiring diagrams for 81,82,83 only.
perhaps corrected for 84.

Site format must have changed because I cant seem to post images like I used to.

kcfong2

Well, for what it's worth, I've deduced my Thermo Time switch is ok. I think the WSM is wrong, and here's why:

The WSM says I should get 0-ohms when grounding terminal W to chassis and terminal G to chassis. It then states I should get 25-40 ohms when measuring across both leads (W+G).

When measuring mine in the car, I was getting 0-ohms and 35 ohms (I can't remember whether it was W or G, but it's irrelevant). I was getting 35 ohms across leads.

I was able to get hold of two (albeit used) thermo time switches, and they measured EXACTLY the same. Then, I stumbled on George Suennen's post (http://928.jorj7.com/icu.html) where he got similar readings.

I find it very unlikely that four thermo-time switches would all be bad or report the same results....

So, my WSM test is: 0-ohms (I think plug W) measured to ground, 30-35 ohms (I think plug G) measured to ground, and 35 ohms measured across W+G.

Anyway, my problem was not the thermo-time switch anyway, but at least now I know how to test it.