Starter upgrade gauge wiring issue

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HTC42

HTC42

Joined
Mar 10, 2026
Threads
8
Messages
43
Location
Willamette valley Oregon
Yesterday, went to start the truck (78 FJ40, de smogged) and the contacts decided to weld themselves together. Replaced the starter with an 80’s gear reduction starter, which only has two wires. The old one had a third… and now my fuel and temp gauge don’t work. I’m assuming this is related. Where would be the best place to get switched power to this circuit be? I tried searching the topic, but didn’t find anything. Apologies if this has been covered. Thanks
 
I know nothing about gear reduction starters. My 72 has a big fat wire from the battery +pos and a regular wire from the ignition switch to make it crank. My regular power is tapped at the battery +pos terminal. Sounds like your regular power is tapped at the starter on the same stud as the big fat wire from the +pos battery - the other wire is from the ignition switch to make it crank.

coolerman's wiring diagrams
 
charliemeyer007 said:
I know nothing about gear reduction starters. My 72 has a big fat wire from the battery +pos and a regular wire from the ignition switch to make it crank. My regular power is tapped at the battery +pos terminal. Sounds like your regular power is tapped at the starter on the same stud as the big fat wire from the +pos battery - the other wire is from the ignition switch to make it crank.

coolerman's wiring diagrams
Click to expand...
I think the wiring is a bit more simple on your truck…
 
rlong said:
The third wire in theory should be 12v to coil while cranking; I do believe it interacts w/ gauges (again in theory it only has 12v that would have come from your old starter upon cranking so useless for anything else.)
Click to expand...
So, in theory I should see whatever voltage I have at the coil on that wire, yes? It’s possible that the two events are unrelated. My gauges have been intermittent. I was hoping a junk starter might be involved.
 
I just moved the truck out to the street to drive it to work tomorrow, and the gauges were back on track so it was a coincidence. The wiring diagram I have is kinda vague in regards to the fuse box. Thanks for the input Y’all!

Btw, the denso gear reduction style is nice!
 
This morning, crank no start. When I got home, it was up to about 60f plus versus 40f. Long crank and lit off as I rolled back from crank. Added a 12v jumper to coil positive and she lit right off. I guess 6v at cranking isn’t enough to excite that coil
 
I went down a rabbit hole of starting (more specifically running issues) issues on my 1978 last year. In an attempt to rectify it, I started with a desmog, and ended with a full rewire. In between, I went through more than one coil / igniter option (and added an ignition relay, a Holley sniper, and a gear reduction starter.

Do you still have the original distributor + igniter + coil setup?

The original 3 connections to the starter are the 10ga BW wire (this comes from your ignition switch), the battery cable (12V+), and then a BY wire connected to the + side of the coil (to do what your jumper essentially did). The other BY wire from your harness to the + side of the coil has a resistor wire in it to reduce voltage on the distributor / igniter / coil under normal running conditions.

The relay I added to resolve this: Cruiser Wiring - https://globalsoftware-inc.com/coolerman/fj40/wiringmainframe.htm

I left the resistor wire and still use a relay after my rewire, but I eliminated the factory igniter setup, and went with a different distributor, added a pertronix igniter and pertronix coil.
 
HTC42 said:
This morning, crank no start. When I got home, it was up to about 60f plus versus 40f. Long crank and lit off as I rolled back from crank. Added a 12v jumper to coil positive and she lit right off. I guess 6v at cranking isn’t enough to excite that coil
Click to expand...
Correct, There is a thread on here recently where someone was / had used a relay to send 12v to the coil while cranking. It would be a simple circuit. Kind on an annoying problem, upgrade starter, lose a function!
 
rlong said:
Correct, There is a thread on here recently where someone was / had used a relay to send 12v to the coil while cranking. It would be a simple circuit. Kind on an annoying problem, upgrade starter, lose a function!
Click to expand...
This one's not recent but it's the right information for the relay, or at least that's what I used. If there is a more current / accurate one, I want to know > Gear Reduction Starter! - https://forum.ih8mud.com/threads/gear-reduction-starter.96018/page-4#post-5071538
 
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