Tach operation with cluster swap

[Beemerdoc]

So, I am working on this 81 stepside and put in a cluster from a 70 something big truck to get a big tach with a small fuel gauge. I got the cluster pinned out correctly, and everything works as intended.

The tach had a separate harness; Black wire (ground), pink w/ black stripe (ignition + current) and a brown (signal). Hooked it all up, and tach goes past the 5000 mark and doesn't move with engine revs. I read where there was a filter needed, and bought one to go between the brown wire and the distributor. No change.

Question: Am I having trouble because the tach originally took a signal from the coil in a points based system and I have HEI? Is there a way to convert the signal? Anyone been here and can help me out?

Thanks in advance for your help.

[motornut]

Originally Posted by Beemerdoc

So, I am working on this 81 stepside and put in a cluster from a 70 something big truck to get a big tach with a small fuel gauge. I got the cluster pinned out correctly, and everything works as intended.

The tach had a separate harness; Black wire (ground), pink w/ black stripe (ignition + current) and a brown (signal). Hooked it all up, and tach goes past the 5000 mark and doesn't move with engine revs. I read where there was a filter needed, and bought one to go between the brown wire and the distributor. No change.

Question: Am I having trouble because the tach originally took a signal from the coil in a points based system and I have HEI? Is there a way to convert the signal? Anyone been here and can help me out?

Thanks in advance for your help.

is it for a 6 cyl?
how high do the revs go?
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[Beemerdoc]

V8 396...not the stock motor. I have no idea what the big truck had for an engine.

[motornut]

got any pics of it
i understand some 6 cyl diesel tachs have less revs "written" on the front
and only go to 4000 not 5000
you mention 5000 so thats sounds right
maybe a part number on the board back...